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Properties of Lignin and Poly(hydroxybutyrate) Blends
A Thesis by Publication submitted in
Partial Fulfilment of the Requirement for the
Degree of
Doctor of Philosophy
Payam Mousavioun
M.Sc., B.Sc. (Chemical Engineering)
Chemistry Discipline
Faculty of Science and Technology
Queensland University of Technology
Queensland, Australia
March 2011
II
III
Acknowledgment
It is a pleasure to thank everybody who made this thesis possible including my
supervisory team, my family and Queensland University of Technology (QUT).
First of all, I would like to express my deepest sense of gratitude to my principal
supervisor, Dr William Doherty, who trusted me and quickly discovered my
potential and interest in the research area. I am heartily thankful to Dr Doherty
whose encouragement, supervision, guidance and support from the preliminary
to the concluding level enabled me to develop an understanding of the subject. I
would also like to acknowledge the support of my associate supervisors,
Professor Graeme George and Professor Peter Halley, during my research
programme. Without their brilliant advice and very timely and valid hints
throughout the completion of my PhD programme, this thesis would not have
been possible. It is an honour for me to have worked with such a great and
prestigious supervisory team.
I would also like to convey my thanks to QUT for providing me with such a
pleasant research area and facilities. I gratefully acknowledge QUT and the
Centre for Tropical Crops and Biocommodities (CTCB) for the financial
assistance of this project through the Postgraduate Research Awards (QUTPRA)
Grant. The assistance of QUT Research Portfolio is also highly appreciated.
I am indebted to many of my colleagues and friends at the Australian Institute
for Bioengineering and Nanotechnology (AIBN), Centre High Performance
Polymers (CHPP) in the University of Queensland (UQ) and CTCB for
providing a warm research atmosphere, sharing of knowledge, and
encouragement. I will never forget the pleasant times I had with my friends
during our meetings at CHPP group at UQ and other social events.
I must acknowledge my beloved wife and best friend, Parastoo. Without her
love, encouragement and assistance, I would not have started and finished this
research programme.
Lastly, I offer my regards and blessings to all of those who have supported me in
any respect during the completion of the project.
IV
Table of Contents
Abbreviations and Nomenclature ............................................................. XVII
Abbreviation ............................................................................................ XVII
Nomenclature ..........................................................................................XVIII
Abstract .................................................................................................
.......................................................................................... XIX
Keywords .................................................................................................
....................................................................................... XXIII
Research Contributions ........................................................................... XXIV
List of Publications..................................................................................... XXV
List of Chapters According to Publications and Contributions ............ XXVII
Scholarship and Grants ........................................................................ XXVIII
Statement of Original Authorship ........................................................... XXIX
CHAPTER 1 ............................................................................................... 1
Introduction ............................................................................................... 1
1.1. Description of Research Problem ............................................................. 2
1.2. Theories and Literature Review ............................................................... 5
1.2.1. Miscibility theories ........................................................................... 5
1.2.2. Kinetics of thermal degradation ........................................................ 7
1.2.3. Literature review .............................................................................. 8
1.2.3.1. Lignin ........................................................................................ 9
1.2.3.2. Poly(hydroxybutyrate) ............................................................. 16
1.2.3.3. Lignin blends ........................................................................... 22
1.2.3.4. PHB blends .............................................................................. 27
1.2.3.5 Studies on the biodegradation of PHB blends ............................ 28
1.2.3.6. Lignin/PHB blends................................................................... 30
1.3. Account of Research Progress Linking the Research Papers .................. 33
1.3.2. Addendum: Kinetics of bagasse decomposition, Lignin
applications .......................................................................................... 34
1.4. References ............................................................................................. 39
V
CHAPTER 2 ............................................................................................. 44
Chemical and thermal properties of bagasse soda lignin ............................. 44
2.1. Introduction ........................................................................................... 45
2.2. Materials and Methods .......................................................................... 47
2.2.1. Lignin extraction ............................................................................ 47
2.2.2. Lignin fractionation ........................................................................ 48
2.2.3. Lignin characterisation methods ..................................................... 49
2.2.3.1. Elemental analysis ................................................................... 49
2.2.3.2. Ash analysis ............................................................................. 49
2.2.3.3. Bulk density ............................................................................. 49
2.2.3.4. Sugar analysis .......................................................................... 50
2.2.3.5. Purity analysis.......................................................................... 50
2.2.3.6. Characterisation of functional groups ....................................... 50
2.2.3.7. Molecular weight determination ............................................... 53
2.2.3.8. Thermogravimetric analysis (TGA) .......................................... 53
2.2.3.9. Differential scanning calorimetry (DSC) .................................. 54
2.3. Results .................................................................................................. 54
2.3.1. The fractionation process ................................................................ 54
2.3.2. Elemental analysis results ............................................................... 54
2.3.3. Molecular weight and functional groups ......................................... 55
2.3.4. Sugar analysis results ...................................................................... 57
2.3.5. Bulk density results ........................................................................ 58
2.3.6. TGA results .................................................................................... 58
2.3.7. Glass transition temperature ............................................................ 61
2.4. Discussion ............................................................................................. 62
2.5. References ............................................................................................. 64
CHAPTER 3 ............................................................................................. 66
Thermal stability and miscibility of poly(hydroxybutyrate) and soda lignin
blends .................................................................................. 66
3.1. Introduction ........................................................................................... 67
3.2. Materials and Methods .......................................................................... 69
3.2.1. PHB................................................................................................ 69
VI
3.2.2. Soda lignin extraction ..................................................................... 70
3.2.3. Lignin characterisation method ....................................................... 70
3.2.3.1. Elemental analysis ................................................................... 70
3.2.3.2. Ash analysis ............................................................................. 71
3.2.3.3. Sugar analysis .......................................................................... 71
3.2.3.4. Characterisation of functional groups ....................................... 71
3.2.3.5. Molecular weight determination ............................................... 72
3.2.4. Blend preparation ........................................................................... 72
3.2.5. Characterisation of blend samples ................................................... 72
3.2.5.1. Thermogravimetric analysis (TGA) .......................................... 72
3.2.5.2. Differential scanning calorimetry (DSC) .................................. 73
3.2.5.3. Scanning electron microscopy (SEM) ...................................... 73
3.2.5.4. Fourier transform-Infrared spectroscopy (FT-IR) ..................... 73
3.3. Results and Discussion .......................................................................... 73
3.4. Conclusion ............................................................................................ 82
Acknowledgments ........................................................................................ 83
3.5. References ............................................................................................. 84
CHAPTER 4 ............................................................................................. 87
Thermophysical properties and rheology of PHB/lignin blends .................. 87
4.1. Introduction ........................................................................................... 88
4.2. Materials and Methods .......................................................................... 89
4.2.1. PHB ................................................................................................ 89
4.2.2. Lignin extraction ............................................................................ 90
4.2.3. Lignin characterisation.................................................................... 90
4.2.4. Blend preparation ........................................................................... 90
4.2.5. Characterisation of blend samples ................................................... 91
4.2.5.1. Thermogravimetric analysis (TGA) .......................................... 91
4.2.5.2. Differential scanning calorimetry (DSC) .................................. 91
4.2.5.3. Rheological analysis ................................................................ 92
4.3. Results and Discussion .......................................................................... 92
4.3.1. Degradation of PHB ....................................................................... 92
4.3.2. Degradation of PHB/lignin blends .................................................. 94
4.3.3. Thermal properties of PHB/lignin blends ........................................ 97
VII
4.3.4. Rheological properties of PHB/lignin blends .................................. 99
4.4. Conclusion .......................................................................................... 104
4.5. References ........................................................................................... 105
CHAPTER 5 ........................................................................................... 107
Environmental degradation of soda lignin/ poly(hydroxybutyrate) blends
........................................................................................... 107
5.1. Introduction ......................................................................................... 108
5.2. Materials and Methods ........................................................................ 110
5.2.1. PHB.............................................................................................. 110
5.2.2. Lignin ........................................................................................... 110
5.2.3. Lignin characterisation ................................................................. 111
5.2.4. Blend preparation ......................................................................... 111
5.2.5. Polymer film fabrication ............................................................... 111
5.2.6. In situ biodegradation of polymer films in soil .............................. 112
5.2.7. Thermogravimetric analysis (TGA) .............................................. 112
5.2.8. Differential scanning calorimetry (DSC) ....................................... 113
5.2.9. X-ray photoelectron spectroscopy analysis.................................... 114
5.2.10. Scanning electron microscopy (SEM) ......................................... 114
5.2.11. Fourier transform-infrared spectroscopy (FT-IR) ........................ 115
5.3. Results and Discussion ........................................................................ 115
5.3.1. Gravimetric analysis ..................................................................... 115
5.3.2. Thermogravimetric analysis .......................................................... 117
5.3.3. Differential scanning calorimetry (DSC) ....................................... 119
5.3.4. XPS analysis ................................................................................. 121
5.3.5. FT-IR analysis .............................................................................. 123
5.3.6. Macroscopic and microscopic changes.......................................... 126
5.4. Conclusion .......................................................................................... 127
Acknowledgements .................................................................................... 127
5.5. References ........................................................................................... 128
CHAPTER 6 ........................................................................................... 131
Thermal stability and miscibility of poly(hydroxybutyrate) and methanol-
soluble soda lignin blends ................................................. 131
VIII
6.1. Introduction ......................................................................................... 132
6.2. Experimental ....................................................................................... 133
6.2.1. PHB .............................................................................................. 133
6.2.2. Lignin extraction .......................................................................... 134
6.2.3. PHB/Lignin blends ....................................................................... 135
6.2.4. Characterisation of blends ............................................................. 135
6.2.4.1. Differential scanning calorimetry (DSC) ................................ 135
6.2.4.2. Thermogravimetric analysis ................................................... 136
6.2.4.3. Scanning electron microscopy (SEM) .................................... 136
6.2.4.4. Fourier transform-Infrared spectroscopy (FT-IR) ................... 136
6.3. Results and Discussion ........................................................................ 136
6.4. Conclusion .......................................................................................... 143
6.5. References ........................................................................................... 144
CHAPTER 7 ........................................................................................... 146
Conclusions and Further Research ............................................................. 146
7.1. Conclusions ......................................................................................... 147
7.1.1. Thermal properties and miscibility study....................................... 147
7.1.2. Thermophysical and rheological properties of lignin/PHB blends . 147
7.1.3. Environmental investigation of lignin/PHB blends ........................ 148
7.1.4. Thermal properties of PHB blends with different types of lignin ... 148
7.2. Future Research ................................................................................... 149
7.2.1. Study of molecular structure of PHB during blend processing ....... 149
7.2.2. Modeling the viscoelasticity of lignin/PHB blends ........................ 149
7.2.3. Study of antimicrobial effect of lignin ........................................... 150
7.2.4. Study of mechanical properties of lignin/PHB blends.................... 150
7.3. References ........................................................................................... 151
APPENDIX 1 ........................................................................................... 152
Thermal decomposition of bagasse. Effect of different sugarcane cultivars
........................................................................................... 152
A.1.1. Introduction ..................................................................................... 153
A.1.2. Experimental ................................................................................... 155
A.1.3. Results and Discussion .................................................................... 158
IX
A.1.3.1. Bagasse composition ................................................................. 158
A.1.3.2. Thermogravimetry (TG) and derivative thermogravimetry (DTG)
analyses .................................................................................................. 159
A.1.3.3. Kinetic study ............................................................................. 167
A.1.4. Conclusion ...................................................................................... 169
A.1.5. References ....................................................................................... 171
APPENDIX 2 ........................................................................................... 174
Value-adding to cellulosic ethanol: Lignin polymers .................................. 174
A.2.1. Introduction ..................................................................................... 175
A.2.2. Lignin Structure ............................................................................... 177
A.2.3. Lignin Fractionation Processes ........................................................ 180
A.2.3.1. Sulfite process........................................................................... 180
A.2.3.2. Kraft process ............................................................................. 182
A.2.3.3. Soda process ............................................................................. 183
A.2.3.4. Other fractionation processes .................................................... 183
A.2.4. Physical Properties of Lignin ........................................................... 185
A.2.5. Applications .................................................................................... 188
A.2.5.1. Protein-lignin blends ................................................................. 191
A.2.5.2. Starch-lignin blends .................................................................. 193
A.2.5.3. Polyhydroxyalkanoates ............................................................. 195
A.2.5.4. Polylactides and polyglycolides ................................................ 197
A.2.5.5. Epoxy resin blends .................................................................... 198
A.2.5.6. Phenol-formaldehyde resins ...................................................... 200
A.2.5.7. Lignin-polyolefin blends ........................................................... 203
A.2.5.8. Lignin-vinyl polymer blends ..................................................... 206
A.2.5.9. Lignin-polyester blends ............................................................. 208
A.2.5.10. Lignin-containing polyurethanes and lignin-polyurethane blends
............................................................................................................... 210
A.2.5.11. Rubber-lignin blends ............................................................... 211
A.2.5.12. Lignin-graft-copolymers ......................................................... 212
A.2.6. Conclusions ..................................................................................... 215
A.2.7. References ....................................................................................... 217
X
List of Figures
Figure 1-1 The description of the process for mixing two polymers.......... 5
Figure 1-2 Cell wall organisation of typical wood presented by Smook
(1934) ................................................................................... 10
Figure 1-3 The molecular repeating unit of cellulose ............................. 10
Figure 1-4 Structure of hemicellulose monomeric sugar units ................ 11
Figure 1-5 Structure of the H-type monomer unit of lignin. Labelled are
the α , β and γ positions of the aryl ether bonds ...................... 13
Figure 1-6 The structure of a possible lignin macromolecule (Glasser, et
al., 1999)............................................................................... 14
Figure 1-7 The structure of the C9 monomer units of lignin. ................... 14
Figure 1-8 Flow scheme of (a) life cycle of PHB, and (b) PHB
manufacturing process (Ghaffar, 2002) ................................. 18
Figure 1-9 Monomer units of PHB, PHV and their copolymer PHBV .... 19
Figure 1-10 DSC cooling and heating curves of pure PHB and PHB/lignin
blend samples ....................................................................... 31
Figure 1-11 Spherulitic growth rate at various crystallisation temperatures
for both a pure PHB and a PHB/lignin blend (Weihua, et al.,
2004) .................................................................................... 32
Figure 1-12 Fractionation process of soda lignin. ..................................... 33
Figure 1-13 Haake mini lab twin extruder ................................................ 35
Figure 2-1 NMR spectrum of an acetylated lignin (L2) fraction ............. 52
Figure 2-2 Size exclusion chromatogrms of lignin and its fractions ........ 56
Figure 2-3 TGA/DTG curve of L1 performed under nitrogen atmosphere
............................................................................................. 59
Figure 2-4 TGA/DTG curve of L2 performed under nitrogen atmosphere
............................................................................................. 60
Figure 2-5 TGA/DTG curve of L3 performed under nitrogen atmosphere
............................................................................................. 60
XI
Figure 2-6 TGA/DTG curve of the starting soda lignin performed under
nitrogen atmosphere.............................................................. 61
Figure 2-7 DSC curves for lignin and its fractions .................................. 61
Figure 3-1 The integral thermogravimetric curves for PHB, soda lignin
and PHB/soda lignin blends. ................................................. 75
Figure 3-2 Plots of T0 and T50 of PHB/soda lignin blends versus soda
lignin content. ....................................................................... 76
Figure 3-3 DSC curves of PHB/soda lignin. ........................................... 77
Figure 3-4 Tgs of PHB and the blends versus soda lignin content. .......... 78
Figure 3-5 SEM image of PHB/soda lignin containing 10 wt% lignin. ... 79
Figure 3-6 SEM image of PHB/soda lignin containing 30 wt% lignin. ... 80
Figure 3-7 SEM image of PHB/soda lignin containing 50 wt% lignin. ... 80
Figure 3-8 FT-IR spectra of the carbonyl stretching region of PHB and
PHB/soda lignin blends. ........................................................ 81
Figure 3-9 Hydrogen bonding interactions between the reactive functional
groups in soda lignin and the carbonyl groups of PHB. ......... 82
Figure 4-1 Isothermal degradation of PHB ............................................. 94
Figure 4-2 Integral thermogravimetric curves for PHB, lignin and 50 wt%
PHB/lignin............................................................................ 95
Figure 4-3 Threshold degradation temperature of PHB/lignin blends ..... 96
Figure 4-4 Activation energy of thermal degradation of PHB/Lignin
blends ................................................................................... 97
Figure 4-5 DSC thermograms of PHB/lignin blends with (a) 40 wt%
lignin, and (b) 80 wt% lignin ................................................ 98
Figure 4-6 Complex viscosity (η *) versus % strain for PHB/10 wt% lignin
........................................................................................... 100
Figure 4-7 Dynamic storage modulus of PHB and PHB/lignin blends .. 100
Figure 4-8 Dynamic loss modulus of PHB and PHB/lignin blends ....... 101
Figure 4-9 Tan δ of PHB and PHB/lignin blends .................................. 102
XII
Figure 4-10 Complex viscosity (η *) of blends of pure PHB and PHB/lignin
blends ................................................................................. 103
Figure 5-1 Buried mass loss of pure and blended PHB with lignin ....... 116
Figure 5-2 Actual and expected mass ratio of lignin/PHB blends after 4
months soil burial. .............................................................. 116
Figure 5-3 Mass ratio on thermal degradation of PHB, lignin, 30 and 60
wt% lignin blends after 4, 8 and 12 months of burial test .... 117
Figure 5-4 PHB random chain scission at temperatures of 170ºC-200ºC
........................................................................................... 118
Figure 5-5 PHB chain scission at temperature of 200ºC- 300ºC ............ 118
Figure 5-6 Survey XPS of (a) PHB and (b) lignin and multiplex scans of
carbon bonds of (c) PHB and (d) lignin ............................... 122
Figure 5-7 Multiplex carbon scan of 20 wt% lignin films at (a) zero time
and (b) 4 months buried. ..................................................... 123
Figure 5-8 FT-IR spectra of (a) PHB, (b) lignin and (c) 4 months buried,
10 wt% lignin/PHB blend ................................................... 124
Figure 5-9 FT-IR spectra of the carbonyl stretching region of (a) Pure
PHB and (b) 10 wt% lignin/PHB blend ............................... 125
Figure 6-1 TGA/DTG curve of ML performed under nitrogen atmosphere.
........................................................................................... 137
Figure 6-2 TGA/DTG curve of PHB performed under nitrogen
atmosphere. ........................................................................ 137
Figure 6-3 The integral thermogravimetric curves for PHB, ML and ML-
PHB blends. ........................................................................ 138
Figure 6-4 DSC curves of ML/PHB blends (refer to Figure 4-5) .......... 139
Figure 6-5 Tgs of PHB and the blends versus ML content. ................... 140
Figure 6-6 SEM image of ML/PHB blend containing 10 wt% ML. ...... 141
Figure 6-7 SEM image of ML/PHB blend containing 30 wt% ML. ...... 141
Figure 6-8 SEM image of ML/PHB blend containing 50 wt% ML. ...... 141
XIII
Figure 6-9 FT-IR spectra of the carbonyl stretching region of PHB and
ML/PHB blends. ................................................................. 142
Figure A.1-1 Thermal decomposition curve of bagasse sample 6987
performed under nitrogen atmosphere ................................. 161
Figure A.1-2 Thermal decomposition curve of bagasse sample 7087
performed under nitrogen atmosphere ................................. 161
Figure A.1-3 Thermal decomposition curve of washed bagasse sample 7087
performed under nitrogen atmosphere ................................. 162
Figure A.1-4 Thermal decomposition curve of bagasse sample 7098
performed under nitrogen atmosphere ................................. 162
Figure A.1-5 Thermal decomposition curve of bagasse sample 7170
performed under nitrogen atmosphere ................................. 163
Figure A.1-6 Thermal decomposition curve of washed bagasse sample 7170
performed under nitrogen atmosphere ................................. 163
Figure A.1-7 Thermal decomposition curve of bagasse sample 7212
performed under nitrogen atmosphere ................................. 164
Figure A.1-8 Friedman’s plot for various α values for sample 6987 ......... 169
Figure A.1-9 A comparison of activation energy as a function of the degree
of conversion (α ) of bagasse samples originating from different
sugarcane cultivars.............................................................. 169
Figure A.2-1 Cellulose strands surrounded by hemicellulose and lignin ... 177
Figure A.2-2 Monolignol monomer species ............................................. 178
Figure A.2-3 Significant lignin linkage structures. ................................... 179
Figure A.2-4 Correlation between the glass transition temperature (Tg) and
the degree of condensation .................................................. 187
Figure A.2-5 Correlation between total aggregate surface area observed per
photo and the solubility parameter of the polymer matrix .... 188
Figure A.2-6 Hydrogen bonding between β-1 stilbene and amylose. ........ 194
Figure A.2-7 Miscibility of lignin/PHB blends based on Tg. .................... 197
XIV
Figure A.2-8 Conversion profiles of lignin-based phenol formaldehyde
resins .................................................................................. 202
Figure A.2-9 Potential sites for hydrogen abstraction for free-radical grafting
from lignin .......................................................................... 213
XV
List of Tables
Table 1-1 Tg values of some different types of lignin (Glasser, et al.,
1999) .................................................................................... 16
Table 2-1 Elemental analysis of lignins (wt%) ...................................... 55
Table 2-2 Lignin fractions formulae...................................................... 55
Table 2-3 Molecular weight averages and function groups .................... 57
Table 2-4 Purity of lignins .................................................................... 58
Table 2-5 Tg of lignin and fractions ...................................................... 62
Table 3-1 Molecular weight of soda lignin and lignin components (wt%)
............................................................................................. 74
Table 4-1 Molecular weight of lignin and lignin components (wt%)
(Mousavioun et al., 2010) ..................................................... 90
Table 4-2 Degradation rate constant of PHB at various temperatures .... 94
Table 4-3 Degradation rate constant of 50 wt% PHB/lignin blends at
various temperatures ............................................................. 96
Table 4-4 Thermal properties of lignin/PHB blends using the starting
lignin material....................................................................... 99
Table 5-1 Molecular weight of lignin and lignin components (wt%)
(Mousavioun et al., 2010) ................................................... 111
Table 5-2 Thermal properties of virgin lignin/PHB blends cast films at
different ratios and biodegraded after 4, 8 and 12 months.... 120
Table 5-3 Macro and Microfilms of PHB and lignin/PHB blends (scale
bar= 15 mm for Macro and 40 µm for Microfilms) ............. 127
Table 6-1 Characterisation of ML ....................................................... 135
Table 6-2 Peak associated with crystalline portion of PHB ................. 142
Table A.1-1 Bagasse sugarcane cultivars and the soil types .................... 156
Table A.1-2 Compositional analysis of pre-dried bagasse samples.......... 158
XVI
Table A.1-3 Energy dispersive spectroscopy results of the elemental
composition of the residues obtained after thermal
decomposition of bagasse ................................................... 165
Table A.1-4 X-ray powder diffraction d-values (Å) for bagasse ash ........ 166
Table A.2-1 Molecular weight and functional groups of lignins .............. 185
Table A.2-2 Tg of different lignin types (Gargulak and Lebo, 2000) ....... 186
Table A.2-3 Application of lignosulfonate products based on their surface-
active properties .................................................................. 188
Table A.2-4 Lignosulfonate products in speciality markets ..................... 189
XVII
Abbreviations and Nomenclature
Abbrev ia t ion AIBN Australian Institute for Bioengineering and Nanotechnology CHPP Centre High Performance Polymers CTCB Centre for Tropical Crops and Biocommodities DMF N,N’ dimethylformamide DSC Differential scanning calorimetry EL Ether-soluble lignin FT-IR Fourier transform-infrared spectroscopy HPLC high performance liquid chromatography L1 diethyl ether fractionated lignin L2 methanol soluble fractionated lignin L3 Residual solvent fractionated lignin Lignin/PHB Blend of lignin and PHB, the same as PHB/lignin ML Methanol-soluble lignin NMR Nuclear magnetic resonance NREL National Renewable Energy Laboratory PE Polyethylene PEO poly(ethylene oxide) PHA Poly(hydroxyalkanoate) PHB Poly(hydroxybutyrate) PHBV poly(hydroxybutyrate-hydroxyvalerate) PHH Poly(hydroxyhexanoate) PHO Poly(hydroxyoctanoate) PHV Poly(hydroxyvalerate) PLA Poly(lactic acid) PP Polypropylene PVA polyvinyl alcohol QUT Queensland University of Technology QUTPRA QUT Postgraduate Research Award RACI The Royal Australian Chemical Institute RL Residual lignin SEM Scanning electron microscopy TGA Thermogravimetric analysis TnBACl tetra-n-butylammonium chloride UQ University of Queensland XPS X-ray photoelectron spectroscopy analysis
XVIII
Nomencla ture
A s�� the pre-exponential factor � - the degree of conversion β
°C min-1 the linear heating rate ∆Hm J g-1 melting enthalpy η * Pa.s complex viscosity E� kJ mol�� apparent activation energy ΔE� kJ mol�� energy of vaporation to a gas at zero pressure G' Pa storage modulus G" Pa loss modulus G��� J Gibbs free energy K�� - Gordon-Taylor equation adjustable parameter K� - Kwei equation adjustable parameter Mn g mol-1 number average molecular weight Mw g mol-1 weight average molecular weight σ - solubility q - Kwei equation adjustable parameter R JK�� mol�� the ideal gas constant S� JK�� entropy T K absolute temperature t min time
Tan δ
- the ratio of energy dissipated to energy stored Tcc °C cold crystal temperature Tg °C glass transition temperature Tm °C melting temperature T�� °C the equilibrium melting point V cm3 volume v! cm3 mol-1 the molar volume w - weight fraction W g weight x - ratio against the % methoxyl (OCH3) content
x%&' - mass ratio of PHB X! - Bulk crystallinity X)! - PHB crystallinity
XIX
Abstract
The Queensland University of Technology (QUT) allows the presentation of a
thesis for the Degree of Doctor of Philosophy in the format of published or
submitted papers, where such papers have been published, accepted or submitted
during the period of candidature. This thesis is composed of Seven
published/submitted papers and one poster presentation, of which five have been
published and the other two are under review. This project is financially
supported by the QUTPRA Grant.
The twenty-first century started with the resurrection of lignocellulosic biomass
as a potential substitute for petrochemicals. Petrochemicals, which enjoyed the
sustainable economic growth during the past century, have begun to reach or
have reached their peak. The world energy situation is complicated by political
uncertainty and by the environmental impact associated with petrochemical
import and usage. In particular, greenhouse gasses and toxic emissions produced
by petrochemicals have been implicated as a significant cause of climate
changes.
Lignocellulosic biomass (e.g. sugarcane biomass and bagasse), which potentially
enjoys a more abundant, widely distributed, and cost-effective resource base, can
play an indispensible role in the paradigm transition from fossil-based to
carbohydrate-based economy.
Poly(3-hydroxybutyrate), PHB has attracted much commercial interest as a
plastic and biodegradable material because some its physical properties are
similar to those of polypropylene (PP), even though the two polymers have quite
different chemical structures. PHB exhibits a high degree of crystallinity, has a
high melting point of approximately 180°C, and most importantly, unlike PP,
PHB is rapidly biodegradable.
Two major factors which currently inhibit the widespread use of PHB are its
high cost and poor mechanical properties. The production costs of PHB are
significantly higher than for plastics produced from petrochemical resources (e.g.
PP costs $US1 kg-1, whereas PHB costs $US8 kg-1), and its stiff and brittle
nature makes processing difficult and impedes its ability to handle high impact.
XX
Lignin, together with cellulose and hemicellulose, are the three main components
of every lignocellulosic biomass. It is a natural polymer occurring in the plant
cell wall. Lignin, after cellulose, is the most abundant polymer in nature. It is
extracted mainly as a by-product in the pulp and paper industry. Although,
traditionally lignin is burnt in industry for energy, it has a lot of value-add
properties. Lignin, which to date has not been exploited, is an amorphous
polymer with hydrophobic behaviour. These make it a good candidate for
blending with PHB and technically, blending can be a viable solution for price
and reduction and enhance production properties. Theoretically, lignin and PHB
affect the physiochemical properties of each other when they become miscible in
a composite. A comprehensive study on structural, thermal, rheological and
environmental properties of lignin/PHB blends together with neat lignin and
PHB is the targeted scope of this thesis. An introduction to this research,
including a description of the research problem, a literature review and an
account of the research progress linking the research papers is presented in
Chapter 1.
In this research, lignin was obtained from bagasse through extraction with
sodium hydroxide. A novel two-step pH precipitation procedure was used to
recover soda lignin with the purity of 96.3 wt% from the black liquor (i.e. the
spent sodium hydroxide solution). The precipitation process is presented in
Chapter 2. A sequential solvent extraction process was used to fractionate the
soda lignin into three fractions. These fractions, together with the soda lignin,
were characterised to determine elemental composition, purity, carbohydrate
content, molecular weight, and functional group content. The thermal properties
of the lignins were also determined. The results are presented and discussed in
Chapter 2. On the basis of the type and quantity of functional groups, attempts
were made to identify potential applications for each of the individual lignins.
As an addendum to the general section on the development of composite
materials of lignin, which includes Chapters 1 and 2, studies on the kinetics of
bagasse thermal degradation are presented in Appendix 1. The work showed that
distinct stages of mass losses depend on residual sucrose. As the development of
value-added products from lignin will improve the economics of cellulosic
XXI
ethanol, a review on lignin applications, which included lignin/PHB composites,
is presented in Appendix 2.
Chapters 3, 4 and 5 are dedicated to investigations of the properties of soda
lignin/PHB composites. Chapter 3 reports on the thermal stability and
miscibility of the blends. Although the addition of soda lignin shifts the onset of
PHB decomposition to lower temperatures, the lignin/PHB blends are thermally
more stable over a wider temperature range. The results from the thermal study
also indicated that blends containing up to 40 wt% soda lignin were miscible.
The Tg data for these blends fitted nicely to the Gordon-Taylor and Kwei
models. Fourier transform infrared spectroscopy (FT-IR) evaluation showed that
the miscibility of the blends was because of specific hydrogen bonding (and
similar interactions) between reactive phenolic hydroxyl groups of lignin and the
carbonyl group of PHB.
The thermophysical and rheological properties of soda lignin/PHB blends are
presented in Chapter 4. In this chapter, the kinetics of thermal degradation of the
blends is studied using thermogravimetric analysis (TGA). This preliminary
investigation is limited to the processing temperature of blend manufacturing.
Of significance in the study, is the drop in the apparent energy of activation, Ea
from 112 kJmol-1 for pure PHB to half that value for blends. This means that the
addition of lignin to PHB reduces the thermal stability of PHB, and that the
comparative reduced weight loss observed in the TGA data is associated with the
slower rate of lignin degradation in the composite. The Tg of PHB, as well as its
melting temperature, melting enthalpy, crystallinity and melting point decrease
with increase in lignin content. Results from the rheological investigation
showed that at low lignin content (≤30 wt%), lignin acts as a plasticiser for PHB,
while at high lignin content it acts as a filler.
Chapter 5 is dedicated to the environmental study of soda lignin/PHB blends.
The biodegradability of lignin/PHB blends is compared to that of PHB using the
standard soil burial test. To obtain acceptable biodegradation data, samples were
buried for 12 months under controlled conditions. Gravimetric analysis, TGA,
optical microscopy, scanning electron microscopy (SEM), differential scanning
calorimetry (DSC), FT-IR, and X-ray photoelectron spectroscopy (XPS) were
used in the study. The results clearly demonstrated that lignin retards the
XXII
biodegradation of PHB, and that the miscible blends were more resistant to
degradation compared to the immiscible blends.
To obtain an understanding between the structure of lignin and the properties of
the blends, a methanol-soluble lignin, which contains 3× less phenolic hydroxyl
group that its parent soda lignin used in preparing blends for the work reported in
Chapters 3 and 4, was blended with PHB and the properties of the blends
investigated. The results are reported in Chapter 6. At up to 40 wt% methanol-
soluble lignin, the experimental data fitted the Gordon-Taylor and Kwei models,
similar to the results obtained soda lignin-based blends. However, the values
obtained for the interactive parameters for the methanol-soluble lignin blends
were slightly lower than the blends obtained with soda lignin indicating weaker
association between methanol-soluble lignin and PHB. FT-IR data confirmed
that hydrogen bonding is the main interactive force between the reactive
functional groups of lignin and the carbonyl group of PHB. In summary, the
structural differences existing between the two lignins did not manifest itself in
the properties of their blends.
XXIII
Keywords
Application Bagasse Biodegradation Biomass Blend Bulk density Burial test Cellulose Characterisation Cold crystallinity Crystallinity Degradation Differencial scanning analysis (DSC) Elemental analysis Environmental Extrusion Fractionation Fourier transform infrared spectroscopy (FT-IR) Glass transition temperature (Tg) Gravimetric analysis Hemicellulose Hydrogen bonding Kinetics Lignin Lignin chemistry Lignocellulose materials Melting point Miscibility Molecular weight Nuclear magnetic resonance (NMR) Poly(hydroxybutyrate) (PHB) Properties Rheological analysis Scanning electron microscopy (SEM) Soda lignin Sugar analysis Sugarcane Sustainability Thermal stability Thermogravimetric analysis (TGA) Viscoelasticity X-ray photoelectron spectroscopy (XPS)
XXIV
Research Contributions
The study on composite materials made from lignin and PHB has added to the
body of knowledge on biodegradable plastics by providing the following
outputs:
Provided information at both the macroscopic and microscopic levels that
was used to explain the properties exhibited by lignin/PHB blends.
Established that the Gordon-Taylor and Kwei models can be used to
predict the Tg of lignin/PHB blends and similar composite materials.
Provided data showing regions of miscibility and immiscibility between
lignin and PHB.
Provided data showing regions where lignin acts a plasticiser for PHB
and regions where it acts as a filler. This has enabled areas for easy
processing of such materials to be identified
Provided information on the environmental performance (i.e.
biodegradability) of lignin/PHB blends.
Published five peer-reviewed articles, with another two articles under
review.
XXV
List of Publications
The following publications have been produced as a result of this thesis.
Peer reviewed journal papers:
1. Payam Mousavioun and William O.S Doherty, “Chemical and thermal
properties of fractionated bagasse soda lignin”, Industrial Crops and
Products, Vol 31, 52-58, 2010. Impact factor, 2.103.
2. Payam Mousavioun, William O.S. Doherty and Graeme A. George,
“Thermal stability and miscibility of poly(hydroxybutyrate) and soda
lignin blends”, Industrial Crops and Products, Vol 32, 656-661, 2010.
Impact factor 2.103.
3. William O.S.Doherty, Payam Mousavioun, Christopher M.Fellows,
“Value-adding to cellulosic ethanol: Lignin polymers”, published in
Industrial Crops and Products, Vol 33, 259-276, 2011. Impact factor
2.103.
4. Vanita R. Maliger, William O. S. Doherty, Ray L. Frost, and Payam
Mousavioun, “Thermal Decomposition of Bagasse: Effect of Different
Sugar Cane Cultivars”, published in Industrial & Engineering Chemistry
Research, Vol 50, 791-798, 2011. Impact factor 1.752.
Peer reviewed journal papers under review:
5. Payam Mousavioun, Peter Halley and William O.S. Doherty,
“Thermophysical properties and rheology of PHB/lignin blends”,
Polymer International, 2011. Impact factor 2.137.
6. Payam Mousavioun, Graeme A. George and William O.S. Doherty,
“Environmental degradation of soda lignin/PHB blends”, Polymer
Degradation and Stability, 2011. Impact factor 2.137.
Published peer reviewed international conference paper:
7. Payam Mousavioun, William O.S. Doherty, Graeme A. George and
Peter Halley, “Thermal stability and miscibility of poly(hydroxybutyrate)
and methanol-soluble soda lignin blends”, presentation in 10th AIChE
XXVI
meeting, Salt Lake City, UT, USA, November 2010. CD Rom. Note that-
publication in AIChE journal is categorised as A class, though the present
work was published as an AIChE proceedings.
Poster presentation:
8. Payam Mousavioun, William O. S. Doherty, Graeme A. George and
Peter Halley “Thermal behaviour of PHB/lignin composites”, Poster
presentation, 11th Pacific Polymer Conference, Cairns, Australia,
December 2009.
X
XV
II
Lis
t o
f C
ha
pte
rs A
cco
rdin
g t
o P
ub
lic
ati
on
s a
nd
Co
ntr
ibu
tio
ns
Pro
pert
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of L
igni
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d P
oly(
hydr
oxyb
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Ble
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Res
earc
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m #
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Cha
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hara
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of l
igni
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frac
tions
Che
mic
al a
nd th
erm
al p
rope
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fr
act
iona
tiona
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gass
e s
oda
lig
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Indu
stria
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ps a
nd P
rodu
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Jan
201
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App
endi
x 1
Kin
etic
s of
ther
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deg
rada
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The
rma
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com
posi
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sse
.
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ngin
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hem
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20
11
App
endi
x 2
App
licat
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of li
gnin
Va
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-add
ing
to c
ellu
lose
eth
ano
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po
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.
Indu
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ps a
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rodu
cts,
Jan
201
1
Res
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m #
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repa
re a
nd c
hara
cter
ise
soda
lign
in/P
HB
ble
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herm
al p
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lign
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The
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ydro
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and
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Indu
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rodu
cts,
Aug
201
0T
herm
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B/li
gnin
com
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tes
11th
Pac
ific
Pol
ymer
Con
fere
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Dec
200
9
Cha
pter
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ogic
al p
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HB
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The
rmop
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s a
nd r
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/lign
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Pol
ymer
Inte
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pre
ss
Cha
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nviro
nmen
tal p
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s of
lign
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HB
ble
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Env
iron
me
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l de
gra
datio
n of
bio
degr
ada
ble
soda
lign
in/P
HB
ble
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Pol
ymer
Inte
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l, In
pre
ss
Cha
pter
7C
oncl
usio
n
poly
(hyd
roxy
buty
rate
) a
nd m
eth
ano
l
XXVIII
Scholarship and Grants
Tuition fee waiver Award from Faculty of Science and Technology,
Queensland University of Technology (QUT), 2008-2011.
QUT Postgraduate Research Award (QUTPRA), 2009-2011.
The Royal Australian Chemical Institute (RACI), grant for attending 11th
Pacific Polymer Conference, Cairns, Australia, 2009.
QUT grant -in-aid for attending 10th AIChE meeting, Salt Lake City, UT,
USA, 2010.
XXIX
Statement of Original Authorship
“The work contained in this thesis has not been previously submitted to meet
requirements for an award at this or any other higher education institution. To
the best of my knowledge and belief, the thesis contains no material previously
published or written by another person except where due reference is made.”
Signature Date
1
CHAPTER 1
Introduction
2
1.1. Descr ip t ion of Research Problem It is now widely accepted that in order to help to reduce global warming it is
necessary to use sustainable environmentally friendly plastics instead of the
traditional petroleum-based ones. Many petroleum-based polymers do not
degrade and are usually decomposed by combustion, thereby adding to the
carbon dioxide levels in the atmosphere. Although there are a few commercially
available biodegradable polymers suitable for commodity applications, their cost
is prohibitive. An example is poly(hydroxybutyrate (PHB). However, PHB has
poor mechanical properties and is difficult to process (Khanna and Srivastava,
2005). The main reasons for its poor properties include (a) low Tg, (b)
undergoes secondary crystallisation which occurs during storage at ambient
temperature, and (c) has a low nucleation density which allows large spherulites,
with cracks and splits, to form. Polymer blending is considered to be one of the
most effective methods for lowering the cost of production of these types of
polymers, and in certain cases improves processing and product quality. The
strategy in this project is to blend lignin, an inexpensive biodegradable
amorphous polymer, with high-value biodegradable aliphatic polyester, PHB,
and to investigate the properties of the blends. The project will, therefore
evaluate the physico-chemical properties of lignins, establish suitable processing
conditions for the preparation of the blends, assess the thermal, mechanical and
rheological properties of the blends, and determine the probable environmental
degradation mechanisms of the blends. The overall benefit from the research is
an improved knowledge on the performance and applicability of lignin-based
composite materials. The research activities have been divided into three main
aims:
• Develop composite materials from lignin by investigating the preparation
and characterisation of soda lignins.
• Prepare, characterise and determine the properties of soda lignin/PHB
blends.
• Prepare, characterise and determine the properties of methanol-soluble
lignin/PHB blends. This is to examine whether the structural differences
3
between soda lignin and methanol-soluble lignin will affect the properties
of the corresponding blends derived from them.
Research Aim #1: Develop composite materials of lignin
Sugar cane fibre, bagasse (a lignocellulosic material), is the fibrous residue from
the sugarcane milling process. The Australian sugar industry harvests around 35
million tonnes of sugarcane a year and this is converted into 5 million tonnes of
sugar, 1 million tonnes of molasses and 10 million tonnes of bagasse. There is
now a focus by the industry to increase the income stream by adding value to the
whole sugarcane biomass, including bagasse. Increasing amounts of surplus
bagasse will therefore become available as the Australian sugar industry
continues to move towards increased energy efficiency. Presently, bagasse is
burned for its fuel value to produce steam and electricity for factory operations.
The cellulose component of bagasse (50% of dry matter) has attracted interest as
a potential source of fuel ethanol. The other component of bagasse is lignin
(20% dry matter), a non-toxic amorphous hydrophobic polymer obtained readily
through extraction methods. Its macromolecular structure and low cost makes
lignin and lignin esters a good candidate for blending with aliphatic polyesters
such as PHB.
Lignin is composed of phenylpropane repeat units and possesses aliphatic and
aromatic hydroxyl groups together with vacant para-sites on the aromatic
monomer unit (section 1.2.3.1). This functionality makes lignin amenable to
chemical reactions. However, for lignin to be used as a feedstock to produce
composite materials of consistent quality, it has to be of high purity, susceptible
to chemical reactions, and of narrow molecular weight distribution. Thus, a
process for lignin isolation and purification from bagasse is a sub-objective in
this project. A number of destructive and non-destructive analytical tools were
used for detailed characterisation of lignin, including its molecular weight and
functionality.
Research Aim #2: Prepare and characterise soda lignin/PHB blends
The incorporation of an amorphous polymer such as lignin or lignin ester should,
in principle, improve the overall properties of PHB by lowering the melting
point, reducing secondary crystallisation, improving processability and reducing
4
brittleness. To optimise processing conditions for the preparation of lignin/PHB
blends, the thermal properties of lignin, the thermal properties of PHB, and the
kinetics of PHB degradation were investigated. The lignin/PHB blends were
assessed by investigating thermal and miscibility properties, as well as
mechanical and rheological properties. Biodegradation studies of the blends
were based on a standard burial soil test.
Research Aim #3: Prepare and characterise methanol-soluble lignin/PHB
blends
The aim of this phase of the project is to study methanol-soluble lignin/PHB
blends in order to establish whether the differences in lignin structure would
affect the properties of lignin/PHB blends. The experimental protocol used to
prepare methanol-soluble lignin/PHB blends was similar to those of soda lignin-
based PHB blends.
A summary of the research plan is outlined as follows: Phase 1 –
Characterisation of lignins; Phase 2 – Preparation, characterisation and
properties of lignin/PHB blends; Phase 3 – Environmental degradation of soda
lignin/PHB blends; Phase 4 – Preparation, characterisation and properties of
methanol-soluble lignin/PHB blends.
5
1.2. Theor ies and L i terature Review
1.2.1. Miscibility theories
Many researchers have studied polymer blending for the development of new
materials and to tailor properties of the blends by exploiting the physical,
chemical, mechanical and thermal properties of the individual components
(Lipatov and Nesterov, 1997).
There are several theories that have been developed to describe compatability
and miscibility of polymers. One of the most famous is the Flory-Huggins
treatment of polymer/solvent interactions in binary polymer systems (Lipatov
and Nesterov, 1997). This theory devised a general scheme which enables one to
deal with the mixing properties of a pair of polymers. It provides a basic
understanding of the occurrence of different types of phase diagrams
independent of temperature and molecular weight. Figure 1-1 illustrates the
process of mixing two polymers, A and B; where nA and nB are moles of the
polymers A and B, and VA and VB are their respective volumes, with V being the
total volume.
Figure 1-1 The description of the process for mixing two polymers
In order to find out whether true mixing would indeed occur, the change in the
Gibbs free energy has to be considered. This change, called the ‘Gibbs free
energy of mixing’ and denoted by ∆-./0, is given by:
nnnnAAAA
VVVVAAAA
nnnnBBBB
VVVVBBBB
nnnnA A A A , , , , nnnnBBBB
V=VV=VV=VV=VAAAA + V+ V+ V+ VBBBB
GGGGAAAA GGGGBBBB GGGGABABABAB
6
∆-./0 2 -45 6 7-4 3 -58 (1-1)
where -4, -5 and -45 denote the Gibbs free energies of the polymers A and B in
separate states and the mixed state, respectively.
The Flory-Huggins treatment represents ∆-./0 as a sum of two contributions:
∆-./0 = 69∆:; + ∆-<=> (1-2)
where the first component 9∆:; is the product of the temperature (T) and the
translational entropy (∆:;), and the second component is the interactions and
motions of the polymers represented by ∆-<=>.
According to equation (1-2), a decrease in ∆-<=> in association with an increase
in ∆:; will lead to a decrease in ∆-./0, which favours miscibility.
Now ∆:; and ∆-<=> can be represented by:
∆:; 2 ?7@4 A BBCD 3 @5 A B
BED8 (1-3)
∆-<=> 2 ?9F7BCBEBGH
8 (1-4)
where ? is the ideal gas constant and I> is the molar volume of a reference unit
(i.e. solvent) common to both polymers. Principally I> can be chosen arbitrarily,
but usually it is identified as the volume occupied by one of the polymer
components in the polymer solution. The decisive factor that describes the
extent of miscibility is the ‘Flory-Huggins interaction parameter’ χ. χ describes
the thermodynamic ‘quality’ of one component to act as a solvent towards
another. Flory-Huggins interaction parameter χ can be estimated from solubility
parameters using the following equation:
χ 2 7KL�KM8MGHNO (1-5)
where σ� σR are the solubility parameters of polymer 1 and polymer 2.
The ability of a polymer to influence the properties of another depends primarily
on its ability to associate and interact with that polymer. Methods for measuring
the association or compatibility on the nano-level (apart from measuring χ)
include electron microscopic techniques and thermal analysis. The presence of
single glass transition temperature (Tg), and the depression of the equilibrium
7
melting point 9.� , and Tm are useful parameters that can also be used to
demonstrate miscibility. The Tg can be determined using differential scanning
calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). In this
study, all measurements of Tg have been undertaken using only DSC instrument.
It was found that the speciments were too brittle to effectively use the DMTA for
the measurement of Tg.
1.2.2. Kinetics of thermal degradation
It is of practical significance to understand and predict the thermal
decomposition process of polymer blends, since this knowledge will help to
better design the engineering process and to estimate the influence on blend
properties by thermal events. It is necessary to consider the kinetics of
decomposition over a wide range of decomposition temperatures. This limits the
use of the conventional isothermal approach. The non-isothermal approach has
the advantage that the decomposition process can be examined at elevated
temperatures and over a wide temperature range. At these temperatures the
degradation process may follow different mechanisms and so provide useful
practical information for the design engineer.
Yao et al. (2008) describes various methods that are used to calculate kinetic
parameters for the thermal decomposition of compounds based on weight loss.
These include first-order decomposition kinetics with different reaction schemes
involving single or multiple constant heating rate methods (i.e. non-isothermal).
For this work, the Friedman’s method (1964) has been used since the method
was applied for the thermal degradation of polymers.
The general rate equation for a decomposition or degradation process can be
described as:
S�S; ~ USVSO 2 W798X7�8 (1-6)
where � is the degree of conversion, U the linear heating rate (°C min-1), W798 is the rate constant and X7�8 is the reaction rate model, a function which
depends on the actual reaction mechanism. The rate constant, W798 can be
calculated by assuming that the temperature and the degree of conversion, � are
non-dependent functions.
8
In this work,
�2 YZ�YYZ�Y[
(1-7)
where \� is the initial weight, \ is the weight during experiment, and \] is the
final weight of the investigation determinate from the TG thermograms.
The rate constant W798can be represented by the Arrhenius equation as:
W798 2 ^_7�`abc8 (1-8)
where de is apparent activation energy (Wf ghi��8, ? is the ideal gas constant
(8.314 fj�� ghi��), ^ is the pre-exponential factor (gk@��) and 9 is absolute
temperature (j).
For a dynamic TGA process, introducing U, into (1-9) results
S�SO 2 74l8_
7�`abc8X7�8 (1-9)
Equations (1-8) and (1-9) are the fundamental expressions of analytical methods
to calculate kinetic parameters on the basis of TGA data.
The Friedman method, which is a linear differential method of equation 1-8, is:
mU S�SOn 2 6 oa
NO 3 7^X7�88 (1-10)
Then for a given value of � the plots of i@ S�S; vs
�O directly leads to 6 oa
N from
the slope.
The main advantage of using Friedman’s approach or any other iso-conversion
method is that de can be calculated for the main degradation process without
any knowledge of the form of the kinetic equation.
1.2.3. Literature review
Introduction
Polymer blending, a process which involves the mixing of two or more
components by solvent casting or melting, is a cost effective technique to tailor-
make materials with improved physical, chemical, mechanical and thermal
properties.
9
Nowadays, with the high price of crude oil and the associated negative impact of
synthetic polymers, increasing attention is being paid to lignocellulosic biomass
as a provider of chemicals and polymers. Lignin is a component of biomass and
its properties can be exploited in the manufacture of polymer blends.
PHB which is generally obtained via fermentation (and in recent times in plants),
is biodegradable. It is envisaged that the incorporation of lignin/lignin-
derivatives into PHB will produce useful polymers for a wide range of
applications. The review presented here is on lignin, PHB and their polymer
blends.
1.2.3.1. Lignin
Introduction
Lignocellulosic materials refer to plants that are composed of cellulose,
hemicellulose and lignin. Sugarcane bagasse, which is comprised of
lignocellulosic compounds, is one of the most promising industrial residues
obtained from the sugar industries (Pandey, et al., 2000). The lignin extracted
from this source is used in the present research investigation.
The wall of a typical lignocellulosic cell is composed of several layers (Figure 1-
2), which are formed as new cells and created at the cambium layer. The middle
lamella is composed mainly of lignin, and serves as the glue bonding adjacent
cells together. The wall itself is made up of a primary wall and a three-layered
secondary wall, each of which has distinct alignments of microfibrils.
Microfibrils are rope like bundles of cellulose molecules, interspersed with and
surrounded by hemicellulose molecules and lignin (Smook, 1934).
10
Figure 1-2 Cell wall organisation of typical wood presented by Smook (1934)
Cellulose (Figure 1-3), which is a polysaccharide and is the main building
material of all plant cells including sugarcane, makes up about 50% of the dry
weight of bagasse (Doherty and Halley, 2004). Since bonding between and
within glucose molecules is so strong, cellulose molecules are very strong.
Lateral hydrogen bonding between cellulose chains is also quite strong, causing
them to group together to form strands that, in turn, form the thicker, rope like
structures called microfibrils (Milton, 1995).
Figure 1-3 The molecular repeating unit of cellulose
Hemicellulose, the second chemical component of bagasse, makes up 30% of its
dry weight (Glasser, et al., 1999). Unlike cellulose, which is made only from
11
glucose, hemicellulose consists of glucose and several other water-soluble
sugars, such as xylose and arabinose (Figure 1-4), produced during
photosynthesis. The degree of polymerisation (that is, the number of sugar
molecules connected together) is lower for hemicellulose than for cellulose and
branched chains rather than straight chains are formed. Hemicellulose surrounds
strands of cellulose and helps in the formation of microfibrils (Milton, 1995).
Figure 1-4 Structure of hemicellulose monomeric sugar units (a) xylose and (b) arabinose
Lignin is the second most abundant organic substance on earth after cellulose,
and plays several important roles in nature. The word lignin was introduced by
de Candolle in 1819 and is derived from the Latin word lignum, meaning wood
(Sjöström, 1993). Lignin stiffens the plant stem to withstand the forces of
gravity and wind, and makes the wood resistant to vermin. Although lignin
provides plants with a protective barrier against being attacked by
microorganisms, it also plays another important role, since it is recycled in the
natural ecology. When it degrades, it serves the soil as a complexing agent for
minerals and as a moisture-retention aid. Lignin also plays a role in the water
conducting system of plants by sealing the water conducting system against the
hydraulic pressure drop produced by the transport of water from the soil to the
leaves (Glasser, et al., 1999). Lignin makes up around 20% of the dry weight of
bagasse.
(a)
(b)
12
Extraction methods of lignin
For lignin to be used to make new products, it must be removed from the plant.
In addition to the diversity of repeat units and bonding patterns which
characterise natural lignin, is the chemical alteration introduced by each method
of removing lignin from the plant. The recovery process to extract lignin from
woody plants changes the chemical and functional group composition of lignin
(Lora and Glasser, 2002) and makes this material extremely heterogeneous.
Methods for recovering lignin are:
• Alkali (soda) process,
• Sulfite process,
• Kraft process,
• Ball milling,
• Enzymatic process,
• Acid digestion and
• Organosolv process.
Different types of lignin have been described depending on the means of
isolation. These include soda lignin, kraft lignin, organosolv lignin,
lignosulfonate, hydrolytic lignin and Klasson lignin. Ball milled lignin is the
best lignin sample among the many isolated lignins that can be used to study the
chemical structure and reactivity of native lignin. However, there have been no
quantitative relationships found between the structural changes in lignin and the
degree of milling. In this project, lignin will be extracted from bagasse using the
soda process, as this is the process of choice in the bagasse biorefinery project
undertaken at Queensland University of Technology, Brisbane, Australia for the
production of bioethanol. Soda lignin is easily recovered by lowering the pH,
filtering and drying. The purity of extracted lignin, as shown in Table 2-4, was
96.3 wt%. The lignin obtained is hydrophobic and contains no sulfur. Its
solubility properties are different from conventional lignosulfonates obtained
through sulfite pulping.
13
The majority of delignification lignin processes (apart from ball milling and
enzymatic process) involve either acid or alkali mechanisms. The
phenylpropane C9 units in lignin are joined by ether linkages, which readily
undergo both acid and base-induced hydrolysis under specific conditions. Side-
chains may be cleaved depending on the type of substructures, particularly under
alkaline conditions (Doherty and Halley, 2004). In the acid delignification
process α-aryl ether substructures are the most readily broken, but it is likely that
β-aryl ether bonds are also broken under strongly acidic conditions (Figure 1-5).
During delignification, components with the functionalisation of the carbonium
ion intermediates are reactions with aromatic structures (weak nucleophiles)
which form carbon-carbon inter-unit linkages and result in condensation
products. The frequency of such condensation reactions increases with the
acidity of the pulping liquor, and decreases with the concentration of the anion
(e.g., bisulfate anions) (Doherty and Halley, 2004).
Figure 1-5 Structure of the H-type monomer unit of lignin. Labelled are the α ,
β and γ positions of the aryl ether bonds
Lignin structure
Lignin is a large, cross-linked, macromolecule with molecular masses in excess
of 10,000 g mol-1. The degree of polymerisation of natural lignin is difficult to
measure, since it is fragmented during extraction, and since the molecule consists
of various types of substructures, which appear to be repeated in a haphazard
manner (Figure 1-6).
14
Figure 1-6 The structure of a possible lignin macromolecule (Glasser, et al., 1999)
There are three monolignol monomers, methoxylated to various degrees: p-
coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol (Quideau and Ralph,
1992) (Figure 1-7). These are incorporated into lignin in the form of the
phenylpropanoids p-hydroxyphenyl (H), guaiacyl (G), and syringal (S)
respectively (Boerjan, et al., 2003).
(a) (b) (c)
Figure 1-7 The structure of the C9 monomer units of lignin. (a) p-coumaryl alcohol (4-hydroxyl phenyl, H), (b) coniferyl alcohol (guaiacyl, G), (c) sinapyl alcohol (syringyl, S).
OH
OH
OH
OH
OCH3 OH
OH
OCH3
OCH3
15
The polymerisation of lignin can produce a number of bond structures by the
delocalization of and reaction at the free radical sites. The lignin produced by
plants depends not only on the species of plant, but the part of the plant as well.
Therefore, lignin of varying composition exists within a single plant. This
means that the lignin recovered from a lignocellulosic plant will be a mixture of
structure and repeat unit composition that will vary with the source of the wood.
Each class of plants, grasses, softwoods, and hardwoods produces a lignin rich in
one or two types of C9 monolignol repeat unit (Doherty and Halley, 2004).
Hardwoods have a lignin that consists almost entirely of G and S type
monomers. Softwoods also have both G and S types, however the major
component is the S type (Boerjan, et al., 2003). The G predominates in grasses,
but also contains some H monomer units, which enables them to be more
flexible in making combinations with other groups.
Sugarcane bagasse lignin is a grass lignin and has a higher proportion of H
groups and hence a lower methoxyl content (i.e. more monomer units with
vacant ortho- and para-sites), than softwood and hardwood. Based on these
chemical structures, lignin is soluble in polar solvents and insoluble in
hydrocarbons, and hence forms immiscible multi-component systems with non-
polar compounds such as polyethylene (PE) and PP (Doherty and Halley, 2004).
The structural heterogeneity of lignin has also been studied by various methods
in a number of investigations. In several of those studies, lignin was subjected to
fractionation prior to analysis. Robert et al. (1984) fractionated kraft lignin by
successive acidification of kraft black liquor, while Moerck et al. (1986) used
organic solvent, Vanderlaan and Thring (1998) fractionated Alcell® lignin with
an organic solvent and Wallberg et al. (2003) used ultrafiltration. These
fractionations were analysed for functional groups, elemental composition and
molecular weight. The results of these investigations showed that the
fractionation process separated the lignin into distinct molecular weights and that
there were differences in the carboxylic acids, phenolic hydroxyl and methoxyl
contents. The properties of the materials produced were dependent on these
structural properties.
16
The Tg is influenced by such factors as the free volume between polymer chains;
the existence and abundance of attractive forces between molecules (which
obviously relates to solubility); the freedom of molecular side groups, branches
and segments to rotate around intermonomer bonds; chain stiffness; and chain
length. The Tg values of some different types of lignin are shown in Table 1-1.
Tab le 1 - 1 Tg va lues o f so me d i f fe ren t t ypes o f l i gn in (G la sse r, e t a l . , 1999)
Types of lignin Tg (ºC)
Lignin in Wood
- Hardwood
- Softwood
65-85
90-105
Milled wood lignin
- Softwood
- Hardwood
138-160
110-130
Periodate lignin 193
Kraft lignin 124-174
Organosolv lignin 91-97
Steam explosion lignin 113-139
1.2.3.2. Poly(hydroxybutyrate)
Introduction
PHB is a polyhydroxyalkanoate (PHA), which belongs to the group of
polyesters. It was first isolated and characterised in 1926 by the French
microbiologist Maurice Lemoigne (1926). PHB is produced by micro-organisms
(such as Alcaligenes eutrophus or Bacillus megaterium), apparently in response
to conditions of physiological stress. The polymer is primarily a product of
carbon assimilation (from glucose or starch) and is utilised by micro-organisms
as a form of energy storage molecule to be metabolized when other common
17
energy sources are not available. Three enzymes (and others) are needed for
production of the PHB polymer. These enzymes include the
3-ketothiolase (PHBA), acetoacetyl-CoA reductase (PHBB), and
polyhydroxybutyrate synthase (PHBC) (Sticklen, 2008).
PHB-producing bacteria require substrates such as ethanol, sucrose, or glucose,
which are costly. In bacteria, PHB is produced in a diluted aqueous solution.
Therefore, the recovery of PHB from diluted fermentation systems adds to the
cost of fermentation as a means of producing PHB. Recently, significant
attempts have been undertaken to produce PHB from plants (Sticklen, 2008).
Plants produce carbon sources via photosynthesis in concentrated products.
Therefore, the costs of production of PHB in plants may become lower than the
costs of its production in bacteria (Sticklen, 2008).
Production of PHB
The manufacturing process of PHB begins with sunlight (Figure 1-8). Through
photosynthesis, atmospheric carbon dioxide is converted to carbohydrates in
either sugar beets or sugarcane. These carbohydrates are the raw material for the
manufacture of PHB. PHB can be produced from glucose as a raw material, or
from agricultural wastes, such as molasses or material refined from the
processing of sugar beets and lactose, or from a wide variety of sources e.g.
volatile fatty acid fermentation products. The sugar is broken down during
metabolism into C2 building blocks, which are converted, over several steps, to
C4 monomers. Finally, the PHB is polymerised.
18
Figure 1-8 Flow scheme of (a) life cycle of PHB, and (b) PHB manufacturing process (Ghaffar, 2002)
The poly-3-hydroxybutyrate (PHB) form of poly(hydroxyalkanoate) (PHA) is
the polymer used in this project. PHB is probably the most common type of
PHA, but many isolation of this class are produced by a variety of organisms:
these include poly-4-hydroxybutyrate (P4HB), polyhydroxyvalerate (PHV),
polyhydroxyhexanoate (PHH), polyhydroxyoctanoate (PHO), and their
copolymers (Figure 1-9).
(a)
(b)
Sugar Beet Sugarcane
Pre-fermentation
19
Figure 1-9 Monomer units of PHB, PHV and their copolymer PHBV
In the future, research using genetic technology, among others, may prove
successful in producing a bacteria-based plastic that has more desirable
properties and is cheaper to produce than PHB. Also, PHB production may
become cheaper if researchers can find a way to make bacteria produce larger
amounts of polymer within shorter time spans or from waste materials using
cheaper production methods. If PHB becomes as cheap as plastics produced
from petrochemicals, then it will probably become widely used, since it has the
potential to be employed for packaging products such as bottles, bags, wrapping
film and disposable nappies (Sykes, 2001).
PHB is also being evaluated as a material for tissue engineering scaffolds and for
controlled drug-release carriers, owing to its biodegradability, limited
cytotoxicity, optical activity and isotacticity (Hasirci, 2003).
There are manyisolation processes that can be used to obtainPHB. Two typical
ones are:
• (1) The extraction method. Mechanical loads are used to destroy the cell
walls and then the polymer is dissolved in chloroform or another solvent
20
such as methyl chloride, 1,2-dichloroethane, pyridine or propylene
carbonate. The remains of the cell must then be separated by
centrifugation and filtration of the solvent.
• (2) Enzymatic method. Enzymes at 37°C destroy the cell wall. The
PHB is then isolated using the same method as that described in previous
section.
Physical and chemical properties of PHB
Some of the main PHB properties are listed below:
• Water insoluble and relatively resistant to hydrolytic degradation. This
differentiates PHB from most other currently available biodegradable
plastics, which are either water soluble or moisture sensitive.
• Good oxygen permeability.
• Good UV resistance but poor resistance to acids and bases.
• Soluble in chloroform and other chlorinated hydrocarbons.
• Biocompatible and hence suitable for medical applications.
• Melting point = 175-177ºC, and Tg = 4ºC.
• Tensile strength of 40 MPa, which is close to that of PP.
• Sinks in water (while PP floats), facilitating its anaerobic biodegradation
in sediments.
• Non-toxic.
Chemistry behind the brittleness of PHB
Crystal structure and crystallisation conditions are responsible for some of the
properties of many PHB products. A sound knowledge and understanding of
crystallisation mechanisms is necessary for designing materials with better
mechanical properties. In practice, crystals formed by polymer molecules are
imperfect. The crystallinity of most melt-crystallised polymers lies in the range
of 30% - 70%. The lamellae thickness can be measured by small angle X-ray
diffraction and directly by electron microscopy. PHB is stiff and brittle with its
brittleness dependent on its Tg, degree of crystallinity and on its microstructure.
21
PHB poses a low nucleation density (Mahendrasingam, et al., 1995, Withey and
Hay, 1999) resulting in the formation of large spherulites. Spherulites contain
crazes, and splitting occurs around the centre of these crazes, hence producing a
significant structural weak point (Barham and Keller, 1986). If PHB is annealed
at high temperatures, stress and brittleness also increases. Another factor which
contributes to the brittle nature of PHB is the fact that it undergoes secondary
crystallisation at room temperature. This process involves the conversion of
amorphous to crystalline material over time, and occurs in PHB because its Tg of
approximately 4°C is close to that of ambient temperature.
22
1.2.3.3. Lignin blends
Introduction
Polymer blending, which involves the mixing of two or more polymeric
components, has been shown to provide the ability to control or tailor properties
to specific desired goals. In many instances, polymer blending results in the
formation of high performance composite materials, this being a consequence of
synergistic interactions. However, many polymer combinations are not miscible
and exist in two different phases in the polymer matrix. The separation into
phases in the polymer matrix results in high interfacial tension and poor
polymer-polymer interactions. This results in materials with poor mechanical
properties, due to poor stress transfer between the phases.
Feldman (2002) reviewed lignin and its polyblends. The review includes phenol
formaldehyde resin-lignin adhesives, epoxy-lignin adhesives, other adhesives
and sealants with lignin, polyolefin lignin blends, polyvinyl chloride/lignin
blends and rubber/lignin blends. Some of these blends are presented here
together with PHB blends and lignin/PHB blends. Since lignin possesses
attractive properties it has been considered by many researchers to provide
compatibility for different polymer types.
Study on miscibility of lignin blends
A very interesting study reported by Pouteau et al. (2004) investigated the
compatibility of lignin-polymer blends by image analysis using visible
spectroscopy. The study looked at the development of lignin-based blends
lignin. It investigated semi-polar polymers (e.g. lignins), very polar polymers
(e.g. starch) and apolar polymers (e.g. PP). The morphology of the blends
obtained from semi polar polymers was very sensitive to the variation of the
solubility parameters. Over a low range of polymer solubility parameters, both
heterogeneous and homogeneous systems were obtained. The properties of the
blends were improved by a careful choice of polymer type. Furthermore, it was
also considered possible to take advantage of lignin variability to improve the
compatibility of the blend. Only low molecular weight lignins were compatible
with a polar and very polar matrix.
23
Kadla et al. (2004) and Kubo et al. (2002) studied the intermolecular interactions
between lignin and synthetic polymers. Their investigations revealed the
immiscible nature of lignin in polyvinyl alcohol (PVA) and PP. However, the
study demonstrated the misciblity behaviour in poly(ethylene oxide) (PEO) and
polyethylene terephthalate (PET), in which the Tg showed a negative deviation
from the linear mixing rule which indicated specific intermolecular interactions.
Furthermore, from these studies Fourier transformed infra red (FT-IR) analysis
revealed strong intermolecular hydrogen bonding between lignin and PET.
Further work by Kadla et al. (2003) investigated the miscibility behaviour over
the entire blend ratio of lignin with PEO. The results of the FT-IR analyses
revealed a strong hydrogen bonding between the aromatic hydroxyl proton of
lignin and the ether oxygen in PEO.
Tinnemans et al. (1984) investigated the mechanical properties of water-
swellable lignin blends. They specifically worked on acylated kraft lignins with
maleic anhydride-styrene copolymers. The resulting blends exhibited a good
tensile strength and demonstrated a high strain at break, owing to favourable
miscibility of the components.
Lignin/PE and lignin/PP blends
Previous attempts at blending PE with lignin in concentrations > 20 wt% yielded
blends with relatively poor mechanical properties. A new method, based on
blending PE with ethylene-vinylacetate (EVA) copolymer has been developed by
Pavol et al. (2004). On the basis of their study, Pavol and co-workers (2004)
found that the addition of 10 wt% EVA caused 200 wt% increase in tensile
strength, and a 1300 wt% increase in elongation at break, compared to those of
the corresponding unmodified samples. Moreover, a composite material
prepared containing 33.6 wt% lignin displayed acceptable processing and
mechanical properties, and was used successfully in preparing blown-films.
Alexy et al. (2000) used lignin as a natural filler in a low-density PE and PP at
concentrations up to 30 wt%. Their study described the influence of lignin
blending on processing stability, mechanical properties and light and long-term
heat degradation, for both polymer blend types. They also showed that different
degradation behaviors between PE-lignin and PP-lignin blends existed. It was
24
determined that lignin concentration influenced both tensile strength and melt
flow index.
The influence of lignin on the oxidative stability of PP and recycled PP has been
examined by Gregorova et al. (2005) using DSC under non-isothermal
conditions. The results showed that lignin exerts a stabilising effect in both
virgin and recycled PP. The protection factor increases with lignin content in the
PP matrix. Moreover, for the evaluation of heat resistance, the influence of the
lignin content on Vicat softening temperature (VST) was determined. VST
showed that the presence of lignin improves the heat resistance of PP and
recycled PP plaques.
The orientation and property correlations of biaxially oriented PE blown films
have been studied by Chen et al. (2006). Correlations between orientation in
both the machine and transverse directions were found with dart impact and
Elmendorf tear strength. These correlations were linked to underlying
morphology and micro-deformation mechanisms.
Košíková et al. (1993) investigated sulfur-free lignins as composites of PP films.
The results showed that PP films containing 2 wt% - 10 wt% spruce organosolv
lignin and/or beech wood prehydrolysis lignin, had good compatibility and
sufficient tensile strength. Also, the physicochemical properties of the lignin-
containing films indicated compatibility between lignin and PP, and
demonstrated that the film acted as a good UV absorber.
Methods for preparing PE blends with organosolv lignin and methods of making
them has been patented by Bono et al. (1995). Another earlier patent by Bono et
al. (1994) involved producing degradable plastic films with ethylene copolymers
and lignin. The lignin was incorporated in the form of very fine powder with a
grain diameter of about 1 µm - 5 µm. The films were homogeneous and
possessed a thickness of about 15 µm - 25 µm. Improved degradation was
achieved with photoactive and oxidizing agents.
Košíková et al. (2001) have reported on the ability of lignin-degrading
microorganisms, phanerochaete chrysosporium, to attack PE in lignin/PE blends.
The isolation of the oligomer fraction from biodegraded polymer blends
25
indicated that the biotransformation of lignin during the cultivation process was
accompanied by the degradation of the PE matrix.
Lignin-polyurethane blends
The morphology of lignin-polyurethane blends has been studied by Feldman et
al. (1989). In this study, although SEM revealed an even distribution of lignin
particles in the polyurethane matrix, it clearly showed the different morphologies
of the constituent phases. The results were confirmed by DSC analysis which
showed immiscibility.
Ciobanu et al. (2004) studied a polyurethane elastomer blended with flax soda
lignin to form dimethylformamide-cast films containing between 4.2 wt% and
23.2 wt% of lignin. The spectral, mechanical and thermal properties of this new
type of blend were investigated in an attempt to establish their potential
applications. Based on that investigation, films containing more than 9.3 wt%
lignin were found to be heterogeneous. The thermal degradation range of
polyurethane and the blends were quite similar. However the presence of lignin
accelerated decomposition at lower temperatures. The tensile strength increased
by up to 370 %, toughness up to 470 % and the elongation at break up to 160 %
for the blends compared to the pure polyurethane film.
Lignin-epoxy blends
Feldman et al. (1991a, 1991b) studied a bisphenol A-polyamine hardener-based
epoxy adhesive modified by kraft lignin. They investigated the curing of these
blends with up to 40 wt% kraft lignin. The curing process was performed either
at room temperature or above the Tg of the components. However, the result was
an enhanced degree of bonding between components, and the reason for the
improvement was thought to be an association between lignin and the unreacted
amine groups of the hardener. In another study, Feldman et al. (1988) observed
that epoxy blends with 10 wt% and 20 wt% lignin improved the adhesion tensile
strength of the epoxy polymer system. However, blending with 5 wt% and 20
wt% lignin had little effect on the adhesive shear strength (by tension loading),
or on the weatherability of the epoxy system. However, after a post curing
process (4 h at 75ºC), a significant improvement of the adhesive strength in shear
of the epoxy-lignin blends was detected.
26
Lignin-based carbon fibres
One of the most interesting applications of lignin is to use it to make carbon-
fibres because of its low cost, high volume and ability to produce fibres, through
melt-spinning. Griffith et al. (2003) studied the use of high-lignin content blends
which could be melt-spun to produce small rows of 10 m - 20 m non-sticking,
drawable filaments. The study was successful and commercial carbon fibres can
now be produced with kraft lignin.
Kadla et al. (2002) reported producing a fusible lignin with excellent spinnability
to form a fine filament following thermal pretreatment under vacuum. Blending
kraft lignin with PEO further facilitated fibre spinning, but at PEO levels
>5 wt%, the blends could not be stabilised without the individual fibres fusing
together. The carbon fibres produced had an overall yield of 45 wt%. The
tensile strength and modulus increased with decreasing fibre diameter, and were
comparable to those of the much smaller diameter carbon fibres produced from
phenolated exploded lignins. In view of its mechanical properties, the tensile
strength of 400 MPa - 550 MPa and the elastic modulus of 30 GPa - 60 GPa,
kraft lignin should be further investigated as a precursor for general grade carbon
fibres.
Effect of UV irradiation on the thermal stability of lignin blends
On the basis of the study by Bittencourt et al. (2005), different films containing
two types of extracted lignin (i.e. kraft lignin and the acetone solvent fraction of
kraft lignin) with different proportions of polyvinyl alcohol (PVA) were
prepared via solvent-casting. The films, with concentrations up to 25 wt%
lignin, were irradiated with UV light for different time intervals. The results of
this analysis indicated better thermal stability and miscibility for the films
prepared with lignin extracted with acetone. This shows that the composition of
the functional group of lignin has a strong bearing on its miscibility behaviour.
A thermal and FT-IR study of polyvinylpyrrolidone (PVP) and bagasse lignin
blends has been undertaken by Silva et al. (2005). The bagasse lignin was
extracted with formic acid and the blends were cast with dimethyl sulfoxide and
formic acid. Blends were also irradiated with UV light. The results showed
miscibility in PVP-lignin blends with 5 wt% lignin content cast from dimethyl
27
sulfoxide, and miscibility in blends containing 5 wt% and 10 wt% lignin cast
from formic acid. Irradiation with UV light resulted in improved thermal
stability.
1.2.3.4. PHB blends
Most studies reported in the literature on PHB blends deal with miscibility,
thermal and mechanical properties. Little has been reported on their
processability and on their rheological properties. This project will investigate
the processability of lignin/PHB blends by studying detailed thermal events,
viscoelastic behavior and storage and loss modulus.
Avella et al. (2000) in a comprehensive review summarizes the properties of
blends of PHB and poly(hydroxybutyrate-hydroxyvalerate) (PHBV). The
mechanical, morphological, and miscibility properties of blends with polyesters,
polyethers, polyvinylacrylates and polysaccharides were studied, as well as the
biodegradation of the blends. The results from the study showed that the
microstructure of the blends controlled the mechanical and biodegradation
behavior of the blends.
Antunes and Felisberti (2005) studied blends of PHB and poly(ε-caprolactone)
(PCL), which is a semi-crystalline polymer that is used as a biomaterial. PHB
and PCL were blended by melting mixtures in an internal mixer. The blends
compositions varied from 0 wt% to 30 wt% PCL. DMTA, DSC and SEM were
used to characterise the blends. The blends were found to be immiscible with no
indication of interaction either in the amorphous or crystalline state. The
morphology of the blends revealed PHB as the matrix and PCL as the dispersed
phase.
El-Taweel et al. (2004) studied the stress-strain behaviour of blends of PHB (of
molar mass 30,000 g mol-1), with different miscible amorphous polymers (of
molar mass 600 g mol-1 to 200,000 g mol-1). They found that a high extension
ratio was obtained only if the PHB content was less than 60 wt%.
Liu et al. (2004) studied the crystallisation of poly(vinylidene fluoride) (PVDF)
and PHB blends using DSC. They found that solid PVDF possibly acts
heterogeneously, nucleating and accelerating PHB crystallisation.
28
An investigation of PHB blends containing starch or starch derivatives has been
reported by Innocentini-Mei et al. (2003). Their work showed a significant
decrease of both the Tg and the melting point (Tm) for all formulations. Best
results in terms of modulus and Tg were obtained with grafted starch-urethane
blends.
The melting and crystallisation behaviour and phase morphology of PHB blends
with poly(DL-lactide)-co-poly(ethylene glycol) (PELA) have been studied by
Zhang et al. (1997). Compared to pure PHB, the cold crystallisation peak
temperatures (Tcc) of PHB blends shifted to higher temperatures. The growth of
spherulites of PHB in the blends was affected significantly by a 60 wt% PELA
content. Similar results were also obtained by Deng et al. (1993).
An investigation on the thermal properties of PHB blends with cellulose esters
containing acetate, propionate, or butyrate substituents has been reported by
Scandola et al. (1993). They observed a good PHB miscibility with the cellulose
esters. The morphology of blends of PHB with cellulose acetate butyrate (CAB)
by compression molding followed by different thermal treatments has been
carried by Tomasi et al. (1995) The results also showed good miscibility
between CAB and PHB.
Yoshie et al. (1995) using high-resolution solid-state carbon-13 nuclear magnetic
resorance (13C-NMR) and proton (1H NMR) spectroscopy observed hydrogen-
bonding interaction in the amorphous phases of PHB and PVA blends. The DSC
measurement confirmed the compatibility of the blends and showed that the
blends have lower crystallinity than the individual polymers.
1.2.3.5 Studies on the biodegradation of PHB blends
Biodegradation of polymer blends is determined both by the degradability of
blend components themselves and by the blend composition. Ikejima et al.
(1999) studied the environmental biodegradability and crystallisation behaviour
of blend films of PHB with chitin and chitosan. The crystallisation behaviour
was similar between blends and with PHB alone. However, several of the blends
showed faster biodegradation than either of the polymer components.
Zhao et al. (2005) studied the effect of aging on the fractional crystallisation of
PEO component in the PEO-PHB blends. Their investigation confirmed that
29
nearly all the PEO component that had remained trapped within the interlamellar
regions of PHB affected aging.
Nagahama et al. (2005) wrote a review on manufactured biodegradable plastics
through forming PVA-PHB blends, fibre-polymer composites and aliphatic
polyester blends. Their work showed effective biodegradation in the composites
made with PHB. Teryshnaya and Shibryaeva (2006) also studied oxidative
degradation of biomicrobial PHB-low density PE and ethylene-PP rubber-PHB
blends. Their results showed improved degradation of the olefins components.
Kikkawa et al. (2006) investigated the enzymatic hydrolysis of poly(L-lactide)
and atactic PHB blends showed that either poly(L-lactide) or atactic PHB
domains were attacked depending on the kind of enzyme used. The larger
number of enzyme molecules was found on poly(L-lactide) domains suggesting
a higher affinity of the enzyme for poly(L-lactide).
Gonvaleves et al. (2009) investigated the biodegradation of PHBV, PP and their
blends in soil. They found the PHBV degraded faster than PP, and that in the
blends, PP only showed changes in the amorphous region.
The type of environment in which the biodegradation is performed has a
significant effect on the rate of degradation. El-Hadi et al. (2002) found that for
blends of PHB and nucleating agents (e.g. tributyrin), aerobic biodegradation
was easier in river water and compost, than in the soil. Imam et al. (1998)
reported that in a natural composite environment, the weight loss correlated with
the amount of starch present in the blends. Imam et al. (1998) also found that
there was no significant difference in molecular weight decrease between neat
PHBV compared to PHBV/starch blends. Imam et al. (1995), on the other hand,
reported that in an activated sludge environment, the rate of weight loss were
quite similar with neat PHBV and PHBV/starch blends.
Recently, Woolnough et al. (2010) studied the biodegradation of PHB and some
other “green plastics” in mature soil detecting mass loss, topographical changes
and biofilm attachments and found that PHB itself has a better degradability
among polyhydroxyoctanoate and poly(DL-lactide) and polystyrene and ethyl
cellulose.
30
1.2.3.6. Lignin/PHB blends
Based on the published information available, there are five articles specifically
relating to lignin and PHB blends. (Camargo, et al., 2002, Ghosh, et al., 2000,
Mihaela, et al., 2010, Naegele, et al., 2000, Weihua, et al., 2004).
Ghosh et al. (2000) investigated the thermoplastic blends of several
biodegradable polymers with lignin and lignin esters, based on both solvent
casting and melt processing. The biodegradable polymer they used contained
cellulose acetate butyrate (CAB), a starch-caprolactone copolymer blend and
PHB. In addition to organosolv lignin, they investigated organosolvo lignin
esters of acetate, butyrate, hexanoate and laurate. They detected a high level of
compatibility between blends of lignin acetate, lignin butyrate and CAB. They
observed a significant amount of retarded crystallisation of PHB with the
addition of lignin, which result in lower melting points of the blends. The
addition of lignin also increased the modulus of the blends significantly at room
temperature, probably because it increased the crystallinity of PHB.
Weihua et al. (2004) investigated the effect of lignin fine powder on the
nucleation of PHB by studying the kinetics under both isothermal and
nonisothermal crystallisation processes. The DSC results showed that lignin not
only acted as a nucleating agent and decreased the activation energy of the
crystallisation process, but it also increased the number of the spherulites formed
(Figures 1-10 and 1-11). However the size of spherulites had decreased.
31
Figure 1-10 DSC cooling and heating curves of pure PHB and PHB/lignin blend samples showing the melt nonisothermal and cold crystallisation temperature, Tmc and Tcc: (A) cooling, and (B) heating (Weihua, et al., 2004)
32
Figure 1-11 Spherulitic growth rate at various crystallisation temperatures for both a pure PHB and a PHB/lignin blend (Weihua, et al., 2004)
Understanding the mechanical and rheological properties of polymer blends is
necessary for understanding changes in the viscoelastic response and
processability conditions.
None of the studies reported to date on lignin/PHB blends have examined in
detail the macroscopic and microscopic associations between lignin and PHB
that would help explain observed thermal, rheological and biodegradation
properties of blends.
33
1.3. Account of Research Progress L inking the
Research Papers This project commenced with a comprehensive literature review of lignin
chemistry, properties and applications. It was evident from the review that
limited work has been carried out with lignin/PHB blends and no biodegradation
evaluation studies for these blends. The following sections link the various
research papers covering the research program.
1.3.1. Chemical and thermal properties of soda lignin
The first step in making lignocellulosics (such as bagasse) amenable to
enzymatic hydrolysis for the production of sugars and subsequently ethanol is to
pretreat it either by mechanical or chemical means. Sodium hydroxide is one of
the pretreatment options used to fractionate lignocellulosics. The advantage of
using sodium hydroxide is that the lignin component of lignocellulosics can
readily be recovered. The lignin recovered by this process has high ash content
and hence is of low purity (Lora and Glasser, 2002). A purification step is
necessary if the soda lignin is to be used in chemical reactions, such as in resin
synthesis. In the present study, a two-stage process was developed which
improved the purity of soda lignin derived from bagasse. Soda lignin produced
by this process was characterised by physical, thermal and chemical means. The
soda lignin was fractionated into three parts using two solvents, diethyl ether and
methanol, which have different polarities. Figure 1-12 shows the flow diagram
for the fractionation process.
Figure 1-12 Fractionation process of soda lignin.
34
Based on this process, only a very small portion of the lignin sample, ~8 wt%,
was recovered using diethyl ether (EL). The major proportion, ~ 68 wt%, was
methanol soluble (ML), and the residue (RL) makes up the remaining 24 wt%.
The results clearly demonstrated the heterogeneity of soda lignin. The two-stage
lignin precipitation process, and the chemical and thermal properties of soda
lignin and its fraction was published in Industrial Crops and Products
(Mousavioun and Doherty, 2010) titled: “Chemical and thermal properties of
fractionated bagasse soda lignin”.
This study on lignin chemistry showed that the lignin with the highest proportion
of phenolic hydroxyl functional group (i.e. ether-soluble lignin) has the highest
potential to interact with PHB to form miscible blends. However, the proportion
of this lignin type in soda lignin was too small to merit investigation.
1.3.2. Addendum: Kinetics of bagasse decomposition, Lignin applications
During the course of the study on the thermal properties of lignin and PHB, it
was established that to obtain optimised conditions for production of lignin/PHB
blends with minimum PHB degradation, the kinetics of PHB degradation should
be studied. Both isothermal and non-isothermal conditions were used in the
study. Similar Ea values for the decomposition process were obtained using both
approaches. As the non-isothermal approach is rapid, it was decided, as an add-
on to the project, to investigate the kinetics of the thermal degradation of bagasse
from which lignin originates. The results of this work were published in
Industrial Engineering & Chemistry Research (Maliger et al., 2011). The title of
the article is, “Thermal decomposition of bagasse. Effect of different sugarcane
cultivars”. The article is presented in Appendix 1. The contribution by the
author of this thesis for this piece of work was 30 wt%.
Having reviewed hundreds of articles on lignin chemistry, properties and uses, a
review paper was deemed necessary to illustrate the potential of lignin-based
polymers for improving the economics of producing cellulosic ethanol from
lignocellulosics. This review paper was published in Industrial Crops and
Products (Doherty, et al., 2011), with the title: “Value-adding to cellulosic
ethanol: Lignin polymers”. The paper is in Appendix 2. The author of this
thesis contributed 20 wt% towards writing the paper.
35
1.3.3. Thermal stability and miscibility of PHB and soda lignin blends
Literature review showed that there were five articles that specifically relate to
lignin and PHB blends (Camargo, et al., 2002, Ghosh, et al., 2000, Mihaela, et
al., 2010, Naegele, et al., 2000, Weihua, et al., 2004). None of these studies
examined the association and interactions between the functional groups of
lignin and those of PHB, which may lead to a better understanding of observed
thermal stability and miscibility properties of lignin/PHB blends.
As mentioned in section 1.3.2, there was concern about the thermal stability of
PHB during processing. So in the 2nd phase of the project, isothermal
degradation tests with PHB were performed at temperatures from 165°C to
190°C. Results showed 175°C was the optimum processing temperature that
will result in minimum PHB degradation.
To produce blends, lignin and PHB were dried at 100°C for 12 h and then stored
in desiccators under vacuum prior to use. Lignin/PHB blends with lignin
contents from 10 wt% to 90 wt% were mixed in a Haake mini lab twin screw
extruder (Figure 1-13) using the procedure reported by Ghaffar (2002). To
minimise PHB degradation, the temperature of the extruder was maintained at
175°C for 2 min. The polymer blends were extruded as strands then cooled and
pelletised. The pellets were stored in a desiccator to avoid moisture absorption,
prior to use.
Figure 1-13 Haake mini lab twin extruder
Feeder
Screw
Heater
Controller
36
In this study, the thermal properties and miscibilities of PHB and soda lignin
blends were investigated by TGA, DSC, SEM and FT-IR over the entire range of
composition. The most important outcome of the study was that lignin reduced
the initial temperature of decomposition of PHB, but stabilised PHB over a wider
temperature range at higher temperatures. This may be because the carbohydrate
components in lignin start to decompose at an earlier temperature than PHB. A
single Tg, which depicts miscibility, was obtained for blends containing up to 40
wt% lignin. The Tg results correlated well with the SEM and FT-IR data. The
FT-IR data showed that the miscibility of the blends is probably associated with
specific hydrogen bonding interactions between the reactive functional groups in
lignin and the carbonyl groups of PHB. This result showed the anticipation of
improvement in properties of PHB by lignin (outcome of phase 1 of the project)
was valid. Results of this work were published in a paper in Industrial Crops and
Products (Mousavioun, et al., 2010), titled “Thermal stability and miscibility of
poly(hydroxybutyrate) and soda lignin blends”.
At this stage of the project it was concluded that lignin, to a certain extent,
improves the thermal properties of PHB. However, the key question still
remained of whether lignin could enhance the rheological properties of PHB and
hence its processibility.
1.3.4. Combination of thermal stability and rheological properties
A comprehension of the rheological properties of polymer blends is required to
determine changes in the viscoelastic responses and determine blend
compositions suitable for easy processing. The miscibility between components
is a significant parameter that dictates viscoelastic responses. Thus, the next
phase of the project was to study the effect of lignin loading on the viscosity of
PHB and its thermophysical properties. The results have been submitted to
Polymer International, titled “Thermophysical properties and rheology of
PHB/lignin blends”. The conclusion drawn from this work is that lignin not only
affects the thermal stability of PHB (based on Ea values, confirming the mass
loss data to some degree), it also affects PHB crystallisation. The rheological
study showed that lignin contents of 10 wt% and 30 wt% plasticise PHB,
resulting in blends having lower viscosities than PHB alone. For blends
37
containing 60 wt% and 90 wt% lignin respectively, lignin acts as a filler, and
blends have viscosities higher than PHB.
1.3.5. Environmental degradation of lignin/PHB blends
In this phase of study, for various compositions of lignin/PHB blends, four
samples were prepared and buried in the soil. The standard burial test method
was used (Woolnough, et al., 2010). Samples were removed every 4 months for
analysis during the 12 months of the trials. The samples were analyzed before
and after exposure, using gravimetric analysis, TGA, DSC, optical microscopy,
SEM, X-ray Photoelectron Spectroscopy (XPS) and FT-IR. The gravimetric
analysis results showed that lignin significantly protects PHB against
degradation, while the DSC results showed that hydrogen bonding of lignin with
PHB plays a significant role to protect PHB against degradation. XPS data
revealed an accumulation of biofilms on the surface of buried film samples.
XPS and FT-IR confirmed that PHB is the most susceptible component against
degradation. FT-IR analysis showed that low lignin contents (<30 wt%)
accelerate PHB degradation, while high lignin contents retard the process. The
results have been explained using the miscibility concept. Results of this work
have been submitted to Polymer Degradation and Stability, titled
“Environmental degradation of lignin/PHB blends”.
1.3.6. Methanol-soluble lignin/PHB blends
This phase of the project examined the impact the composition of the functional
groups of lignin influenced the properties of lignin/PHB blends. Soda lignin
contains 3× the proportion of xylan and phenolic hydroxyl group than ML. It
however, has 1.5× less carboxylic acid groups. ML/PHB blends with lignin
contents from 10 wt% to 90 wt% were assessed in a similar fashion as soda
lignin/PHB blends. The result of the study was presented and published as a full
paper in the Proceedings (CD-ROM) at the 10th AIChE Annual meeting, Salt
Lake City, UT, USA. The title of the paper is: “Thermal stability and miscibility
of poly(hydroxybutyrate) and methanol-soluble soda lignin blends”.
38
The T0 values of ML/PHB blends were higher than the T0 values of soda
lignin/PHB blends. This may be because of the proportion of xylan in the
composite. Xylans are known to decompose at lower temperatures than
cellulose and lignin.
Tg results of ML/PHB blends indicated that blends containing up to 40 wt% ML
are miscible with PHB. The similar results were obtained for soda lignin/PHB
blends (section 1.3.3). FT-IR spectra showed that for blends up to 50 wt% ML,
there was a small but definitive shift to lower wavenumbers, indicating hydrogen
bonding interactions. The similarities between the results and those of
lignin/PHB blends indicated that the differences observed in the composition of
lignin functional groups were not significant to influence the glass transition
temperature of lignin/PHB blends derived from the two lignin types.
39
1.4. References
Alexy, P., Kosíková, B., Podstránska, G., 2000. The effect of blending lignin with polyethylene and polypropylene on physical properties. Polymer 41, 4901-4908.
Antunes, M.C.M., Felisberti, M.I., 2005. Blends of poly(hydroxybutyrate) and poly(ε-caprolactone) obtained from melting mixture. Polym. Sci. Technol. 15, 134-138.
Avella, M., Martuscelli, E., Raimo, M., 2000. Review Properties of blends and composites based on poly(3-hydroxy)butyrate (PHB) and poly(3-hydroxybutyrate-hydroxyvalerate) (PHBV) copolymers. Journal of Materials Science 35, 523-545.
Barham, P.J., Keller, A., 1986. The relationship between microstructure and mode of fracture in polyhydroxybutyrate. J. Polym. Sci. Part B: Polym. Phys. 24, 69-77.
Bittencourt, P.R.S., dos Santos, G.L., Gómez Pineda, E.A., Winkler Hechenleitner, A.A., 2005. Studies on the thermal stability and film irradiation effect of poly(vinylalcohol)/kraft lignin blends. J. Ther. Anal. and Calori. 79, 371-374.
Boerjan, W., Ralph, J., Baucher, M., 2003. Lignin biosynthesis. Ann. Rev. Plant Biol. 54, 519-549.
Bono, P., Feldman, D., Banu, D., Lora, J.H., Wang, J., Wu, C.F., 1995. Degradable polymers and polymer products. WO 1995034604
Bono, P., Lambert, C., 1994. Degradable plastics film including lignin as active vegetable filler. US 5321065.
Camargo, F.A., Lemes, A.P., Moraes, S.G., Mei, L.I., Duran, N.,2002. Characterization and biodegradation of blend synthesize from naturals Polymers. In: International symposium on Natural Polymers and Composites, Sao Carlos, Brazil, pp. 49-54.
Chen, H.Y., Bishop, M.T., Landes, B.G., Chum, S.P., 2006. Orientation and property correlations for LLDPE blown films. J. Appl. Polym. Sci. 101, 898-907.
Ciobanu, C., Ungureanu, M., Ignat, L., Ungureanu, D., Popa, V.I., 2004. Properties of lignin-polyurethane films prepared by casting method. Ind. Crops and Prod. 20, 231-241.
Deng, X., Zhang, L., Xiong, C., 1993. Miscibility and crystallization behavior of biodegradable blend of poly(β -hydroxybutyrate) and poly(D,L-lactide)-co-poly(ethylene glycol). Chin. Chem. Lett. 4, 265-8.
Doherty, W.O.S., Halley, P., 2004. Lignin technology and market assessment for directing research in CRC sugar industry innovation project. SRI Job No. 3247.
Doherty, W.O.S., Mousavioun, P., Fellows, C.M., 2011. Value-adding to cellulosic ethanol: Lignin polymers. Ind. Crops prod. 33, 259-276.
El-Hadi, A., Schnabel, R., Straube, E., Müller, G., Henning, S., 2002. Correlation between degree of crystallinity, morphology, glass temperature, mechanical properties and biodegradation of poly (3-hydroxyalkanoate) PHAs and their blends. Polymer Testing 21, 665-674.
40
El-Taweel, S.H., Stoll, B., Hoehne, G.W.H., Mansour, A.A., Seliger, H., 2004. Stress-strain behavior of blends of bacterial polyhydroxybutyrate. J. Appl. Polym. Sci. 94, 2528-2537.
Feldman, D., 2002, Lignin and its polyblends - a review, In: Chemical, Modification, Properties, and Usage of Lignin, Kluwer Academic/Plenum Publishers, USA.
Feldman, D., Banu, C.D., Natansohn, A., Wang, J., 1991a. Structure-properties relations of thermally cured epoxy-lignin polyblends. J. Appl. Polym. Sci. 42, 1537-1550.
Feldman, D., Banu, C.D., B., Wang, L.J., 1991b. Epoxy-lignin polyblends: Correlation between polymer interaction and curing temperature. J. Appl. Polym. Sci. 42, 1307-1318.
Feldman, D., Lacasse, M.A., 1989, Morphology of lignin-polyurethane blends, In: Materials Research Society Symposium Proceedings, Canada.
Feldman, D.K., M., 1988. Epoxy-lignin polyblends. Part II. Adhesive behavior and weathering. J. Adh. Sci. Tech. 2, 107-116.
Ghaffar, A.M.E.A., 2002, Development of a biodegradable material based on Poly(3-hydroxybutyrate) PHB, In, Martin-Luther University, Wittenberg, pp. 115.
Ghosh, I., Jain, R.K., Glasser, W.G., 2000. Multiphase materials with lignin. Part 16. Blends of biodegradable thermoplastics with lignin esters. ACS Symp. Ser. 742, 331-350.
Glasser, W.G., Northey, R.A., Schultz, 1999. Lignin: Historical, Biological, and Material prespectives, Washing, DC.
Gonçalves, S., Martins-Franchetti, S., Chinaglia, D., 2009. Biodegradation of the Films of PP, PHBV and Its Blend in Soil. Journal of polymers and the environment 17, 280-285.
Gregorová, A., Cibulková, Z., Kosíková, B., Simon, P., 2005. Stabilization effect of lignin in polypropylene and recycled polypropylene. Polym. Degrad. Stab. 89, 553-558.
Griffith, W.L., Compere, A.L., Leitten, C.F., Jr., Shaffer, J.T., 2003, Low-cost, lignin-based carbon fiber for transportation applications, In: International SAMPE Technical Conference, Society for the Advancement of Material and Process Engineering, USA.
Hasirci, V., 2003. Poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) based tissue engineering matrices. J. M. Sci.: Materials in Medicine 14, 121-126.
Henry, L.F., 1964. Kinetics of thermal degradation of char-forming plastics from thermogravimetry. Application to a phenolic plastic. J. Polym. Sci., Part C: Polym. Symp. 6, 183-195.
Ikejima, T., Inoue, Y., 1999. Crystallization behavior and environmental biodegradability of the blend films of poly(3-hydroxybutyric acid) with chitin and chitosan. Carbohydr. Polym. 41, 351-356.
Imam, S.H., Chen, L., Gordon, S.H., Shogren, R.L., Weisleder, D., Greene, R.V., 1998. Biodegradation of Injection Molded Starch-Poly (3-hydroxybutyrate-co-3-hydroxyvalerate) Blends in a Natural Compost Environment. Journal of polymers and the environment 6, 91-98.
Imam, S.H., Gordon, S.H., Shogren, R.L., Greene, R.V., 1995. Biodegradation of starch-poly(β-hydroxybutyrate-co-valerate) composites in municipal activated sludge. Journal of polymers and the environment 3, 205-213.
41
Innocentini-Mei, L.H., Bartoli, J.R., Baltieri, R.C., 2003. Mechanical and thermal properties of poly(3-hydroxybutyrate) blends with starch and starch derivatives. Macromol. Symp. 197, 77-87.
Kadla, J.F., Kubo, S., 2003. Miscibility and Hydrogen Bonding in Blends of Poly(ethylene oxide) and Kraft Lignin. Macromolecules 36, 7803-7811.
Kadla, J.F., Kubo, S., 2004. Lignin-based polymer blends: analysis of intermolecular interactions in lignin-synthetic polymer blends. Composites Part A 35, 395-400.
Kadla, J.F., Kubo, S., Venditti, R.A., Gilbert, R.D., Compere, A.L., Griffith, W., 2002. Lignin-based carbon fibers for composite fiber applications. Carbon 40, 2913-2920.
Khanna, S., Srivastava, A.K., 2005. Recent advances in microbial polyhydroxyalkanoates. Process Biochemistry 40, 607-619.
Kikkawa, Y., Suzuki, T., Tsuge, T., Kanesato, M., Doi, Y., Abe, H., 2006. Phase structure and enzymatic degradation of poly(L-lactide)/atactic poly(3-hydroxybutyrate) blends: an atomic force microscopy study. Biomacromolecules 7, 1921-8.
Košíková, B., Alexy, P., Mikulášová, M., Kačík, F., 2001. Characterization of biodegradability of lignin-polyethylene blends. Wood Research 46, 31-36
Košíková, B., Demianová, V., Kacuráková, M., 1993. Sulfur-free lignins as composites of polypropylene films. J. Appl. Polym. Sci. 47, 1065-1073.
Kubo, S., Kadla, J.F., Gilbert, R.D., 2002, Thermal-blending of lignin with hydrophilic polymers, In: 223rd ACS National Meeting, American Chemical Society, USA.
Lemoigne, M., 1926 Products of dehydration and of polymerization of β-hydroxybutyric acid. Bull. Soc. Chim. Belg. 8, 770-82.
Lipatov, Y., S., Nesterov, A.E., 1997. Thermodynamics of polymer blends Technomic, Lancaster, PA
Liu, J., Qiu, Z., Jungnickel, B.J., 2004. Crystallization and morphology of poly(vinylidene fluoride)/poly(3-hydroxybutyrate) blends. III. Crystallization and phase diagram by differential scanning calorimetry. J. Polym. Sci., Part B: Polym. Phys. 43, 287-295.
Lora, J.H., Glasser, W.G., 2002. Recent industrial application of lignin. J. polym. and env. 10, 39-48.
Mahendrasingam, A., Martin, C., Fuller, W., Blundell, D.J., MacKerron, D., Rule, R.J., Oldman, R.J., Liggat, J., Riekel, C., Engstrom, P., 1995. Microfocus X-ray Diffraction of Spherulites of Poly-3-hydroxybutyrate. J. Synchr. Rad. 2, 308-312.
Mihaela, C., Vasile, C., Agafitei, G.E., Cazacu, G., Stoleriu, A., 2010. Compatibility and degradability of the polyalkanoates/epoxy modified lignin blends Polym. Yearb. 23, 265-282.
Milton, F., 1995, The Preservation of Wood. A Self Study Manual for Wood Treaters, College of Natural Resources, In, Minnesota Extension Service, University of Minnesota College of Natural Resources, St. Paul, MN, USA pp. 102.
Moerck, R., Yoshida, H., Kringstand, K.P., Hatakeyama, H., 1986. Fractionation of kraft lignin by successive extraction with organic solvents, 1. Functional groups, 13C-NMR-spectra and molecular weight distributions. Holzforschung 40, 51-60.
42
Mousavioun, P., Doherty, W.O.S., 2010. Chemical and thermal properties of fractionated bagasse soda lignin. Ind. Crops Prod. 31, 52-58.
Mousavioun, P., Doherty, W.O.S., George, G., 2010. Thermal stability and miscibility of poly(hydroxybutyrate) and soda lignin blends. Ind. Crops Prod. 32, 656-661.
Naegele, H., Pfitzer, J., Eisenreich, N., Eyerer, P., Elsner, P., Eckl, W., 2000. Plastic material made from polymer blend Denmark WO 0027923.
Nagahama, M., Takebayashi, K., 2005. Recent trend of biodegradable plastics. Kagaku Sochi 47, 81-86.
Pandey, A., Soccol, C.R., Nigam, P., Soccol, V.T., 2000. Biotechnological potential of agro-industrial residues. I: sugarcane bagasse. Bioresource Technol. 74, 69-80.
Pavol, A., Bozcaron, K., Gabriela, C., Adriána, G., Pavol, M., 2004. Modification of lignin-polyethylene blends with high lignin content using ethylene-vinylacetate copolymer as modifier. J. Appl. Polym. Sci. 94, 1855-1860.
Pouteau, C., Baumberger, S., Cathala, B., Dole, P., 2004. Lignin-polymer blends: evaluation of compatibility by image analysis. Comptes Rendus Biologies 327, 935-943.
Quideau, S., Ralph, J., 1992. Facile large-scale synthesis of coniferyl, sinapyl, and p-coumaryl alcohol. J. Agric. Food Chem. 40, 1108-1110.
Robert, D.R., Bardet, M., Gellerstedt, G.r., Lindfors, E.L., 1984. Structural Changes in Lignin During Kraft Cooking Part 3. On the Structure of Dissolved Lignins. J. W. Chem. and Tech. 4, 239-263.
Scandola, M., Pizzoli, M., Ceccorulli, G., 1993. Thermal properties of polymer blends based on biodegradable bacterial polyesters. Calorim. Anal. Therm. 24, 433-6.
Silva, M.F., da Silva, C.A., Fogo, F.C., Pineda, E.A.G., Hechenleitner, A.A.W., 2005. Thermal and FTIR study of polyvinylpyrrolidone/lignin blends. J. Therm. Anal. and Calorim. 79, 367-370.
Sjöström, E., 1993. Wood chemistry–fundamentals and applications, Academic Press, San Diego.
Smook, G.A., 1934. Handbook for pulp & paper technologists, Angus Wilde Publications, Vancouver.
Sticklen, M.B., 2008, Mariam Sticklen's Home Page, In: Biofuel & Biopharmaceutical Crop Genetic Engineering Lab, Dept. of Crop and Soil science, East Lansing.
Sykes, K., 2001, Plastics you could eat - recycling, In: First science.com. Tertyshnaya, Y.V., Shibryaeva, L.S., 2006. Use of differential scanning
calorimetry to study oxidation of polymer mixtures. Plast. Massy 46-48. Tinnemans, A.H.A., Greidanus, P.J., 1984, Chemically modified lignin for the
use in polymer blends, In: Comm. Eur. Communities, Inst. Appl. Chem., Utrecht, Neth., pp. 492-494.
Tomasi, G., Scandola, M., 1995. Blends of bacterial poly(3-hydroxybutyrate) with cellulose acetate butyrate in activated sludge. Plast. Eng. (N. Y.) 29, 79-89.
Vanderlaan, M.N., Thring, R.W., 1998. Polyurethanes from Alcell® lignin fractions obtained by sequential solvent extraction. Biomass Bioenergy 14, 525-531.
43
Wallberg, O., Jönsson, A.S., Wimmerstedt, R., 2003. Fractionation and concentration of kraft black liquor lignin with ultrafiltration. Desalination 154, 187-199.
Weihua, K., He, Y., Asakawa, N., Inoue, Y., 2004. Effect of lignin particles as a nucleating agent on crystallization of poly(3-hydroxybutyrate). J. Appl. Polym. Sci. 94, 2466-2474.
Withey, R.E., Hay, J.N., 1999. The effect of seeding on the crystallisation of poly(hydroxybutyrate), and co-poly(hydroxybutyrate-co-valerate). Polymer 40, 5147-5152.
Woolnough, C.A., Yee, L.H., Charlton, T., Foster, L.J.R., 2010. Environmental degradation and biofouling of ‘green’ plastics including short and medium chain length polyhydroxyalkanoates. Polym. Int. 59, 658-667.
Yao, F., Wu, Q., Lei, Y., Guo, W., Xu, Y., 2008. Thermal decomposition kinetics of natural fibers: Activation energy with dynamic thermogravimetric analysis. Polym. Degrad. Stab. 93, 90-98.
Yoshie, N., Azuma, Y., Sakurai, M., Inoue, Y., 1995. Crystallization and compatibility of poly(vinyl alcohol)/poly(3-hydroxybutyrate) blends: influence of blend composition and tacticity of poly(vinyl alcohol). J. Appl. Polym. Sci. 56, 17-24.
Zhang, L., Deng, X., Zhao, S., Huang, Z., 1997. Biodegradable polymer blends of poly(3-hydroxybutyrate) and poly(DL-lactide)-co-polyethylene glycol. J. Appl. Polym. Sci. 65, 1849-1856.
Zhao, L., Kai, W., He, Y., Zhu, B., Inoue, Y., 2005. Effect of aging on fractional crystallization of poly(ethylene oxide) component in poly(ethylene oxide)/poly(3-hydroxybutyrate) blends. J. Polym. Sci., Part B: Polym. Phys. 43, 2665-2676.
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44
CHAPTER 2
Chemical and thermal properties of
bagasse soda l ignin
Payam Mousavioun and W.O.S. Doherty
Centre for Tropical Crops and Biocommodities, Queensland University of
Technology, GPO Box 2434, Brisbane, Australia
Published in Industrial Crops and Products, Vol 31, Page 52, 2010
45
Abstract- A major challenge of the 21st century will be to generate
transportation fuels using feedstocks such as lignocellulosic waste materials as a
substitute for existing fossil and nuclear fuels. The advantages of
lignocellulosics as a feedstock material are that they are abundant, sustainable
and carbon-neutral. To improve the economics of producing liquid
transportation fuels from lignocellulosic biomass, the development of value-
added products from lignin, a major component of lignocellulosics, is necessary.
Lignins produced from black liquor through the fractionation of sugarcane
bagasse with soda and organic solvents have been characterised by physical,
chemical and thermal means. The soda lignin fractions have different physico-
chemical and thermal properties from one another. Some of these properties
have been compared to bagasse lignin extracted with aqueous ethanol.
2.1. I ntroduct ion In the last century, energy sources have been derived from petroleum (30 %),
natural gas (23 %), coal (22 %), renewable (19 %) and nuclear (6 %) (Song,
2002). In the chemical industry, 4 % of crude oil and 31 % of natural gas are
used in the manufacture of platform chemicals and composite materials. The
state of the oil market ($US40-$US100 per barrel) is unpredictable because of
economic and political pressures, and the ever increasing oil demand from
developing Asian countries will probably maintain the current high price of
crude oil. There is the ongoing debate among geologists as to the time frame
when oil reserves will be depleted. There is also the strong push towards
reduced greenhouse gas (GHG) emission. Fossil fuels used in transportation
contribute over 25 % of GHG. It has been estimated that the utilisation of
plant/crop-based feedstock for the production of chemicals in the European
Union could deliver GHG reductions of over 6 M tonnes per annum in the next
decade. As a consequence of these events, there has been coordinated R&D
strategy across the globe for the utilisation of plant/crop-based products.
The International Energy Agency, Energy Outlook in November 2006 stated,
“Rising food demand, which competes with biofuels for existing arable and
pasture land, will constrain the potential for biofuels production using current
technology”. Such a constraint causes feedstock price increase for both food and
46
fuel. So the challenge we now have is to be able to produce transportation fuels
from non-food sources e.g., bagasse, wheat straw, rice stalk, cotton linters,
agricultural wastes, and forest thinning, at an economically competitive price
without government subsidies. To bring down production cost of biofuels,
developing a market for lignin products which have equivalent properties as the
petroleum-based products is necessary.
In 2006, the world produced 1.4 billion tonnes of sugarcane (FAO, 2009). This
equates to ~400 million tonnes of bagasse. Currently, a vast majority of bagasse
is used to produce low value co-generation of power, manufacture of pulp and
paper products and furfural production. However, with continuing
improvements in energy efficiencies of sugar factories, more and more bagasse
will be available for other applications, such the production of cellulosic ethanol.
The advantage bagasse has over other non-food sources is that it is located
centrally due to existing transportation infrastructure. So, co-location of a
cellulosic ethanol plant to a sugar factory gives the opportunity to share
production systems but also to share processing facilities.
Bagasse, a non-wood, consists mainly of cellulose (50 wt%), hemicellulose (30
wt%) and lignin (20 wt%). Lignin is an amorphous large, cross-linked,
macromolecule with molecular masses in the range 1000 g mol-1 to 20,000 g
mol-1. The degree of polymerisation in nature is difficult to measure, since it is
fragmented during extraction and the molecule consists of various types of
substructures which appear to repeat in a haphazard manner. There are three
monolignol monomers, methoxylated to various degrees: p-coumaryl alcohol,
coniferyl alcohol, and sinapyl. Despite improvements in structure elucidation,
the exact structure of lignin is still unknown. The consensus by a number of
workers (Adler, 1980; Sjostrom, 1981; Chen, 1991; Ede and Kilpelaeinen, 1995;
Karhunren et al., 1995a; Karhunren et al., 1995b) is that the two commonest
linkages are ether and carbon-carbon bonds. The phenylpropane β-aryl ether
linkages constitute the largest proportion of the different linkages connecting the
monomeric units. These linkages need to be broken for effective lignin
fractionation from biomass.
The processes used in the extraction of lignin from woody plants are conducted
under conditions were lignin is progressively broken down to lower molecular
47
weight fragments resulting to changes to its physico-chemical properties. Thus,
apart from the source of the lignin, the solvating ability of the solvent to either
lignin or the cellulose, or both, the properties of the solvent to inhibit to C-C
bond formation, the solution pH and the method of extraction influences the
chemical and functional group composition of lignin. Gosselink et al. (2004)
have reported that lignin composition is different not only among plants but also
different between parts of the same plant. The structural heterogeneity of lignin
has also been studied by various methods in a number of investigations. In
several of these studies the lignin was subjected to fractionation prior to the
analysis (Robert et al., 1984; Moerck et al., 1986; Vanderlann and Thring, 1998;
Wallberg et al., 2003). These fractionations were analysed for functional groups,
elemental composition and molecular weight. The results of these investigations
showed that the fractionation process separated the lignin into distinct molecular
weights and that there were differences in the carboxylic acids, phenolic
hydroxyl and methoxyl contents The properties of the materials produced were
dependent on these structural properties
As one of our research goals is to produce cellulosic ethanol from bagasse via
pretreatment with soda and add value to lignin, we have undertaken a
characterisation exercise on soda lignin and examined its heterogeneity through
sequential extraction in order to target products based on structure-property
relationships. Where possible we have compared the results to that of bagasse
lignin obtained through aqueous ethanol extraction, as the lignin obtained by this
process is generally regarded to be of good quality.
2.2. Mater ia ls and Methods
2.2.1. Lignin extraction
Bagasse was obtained from a Mackay Sugar Mill, Queensland Australia. It was
wet depithed and then air dried. Lignin was extracted from bagasse by the soda
process using a 20 L Parr reactor. In this method, 1 kg of bagasse is reacted with
~10.5 L of 0.7 - 1 M NaOH. Once the reactor reaches the operating temperature
of 170°C, it is maintained for 1.5 h. After cooling, the liquid (black liquor) was
removed from the bottom of the reactor and sieved to remove fibrous material.
48
To the black liquor, dilute sulfuric acid was slowly added with stirring to pH 5.5.
Near pH 5.5 an obvious change in the appearance of the solution occurs from
black to murky brown. This change is due to the initial stages of lignin
precipitation. The mixture was stirred for 10 min - 15 min after which
acidification was continued to pH 3. It was then transferred to a 65°C water bath
and stirred using an overhead stirrer for 30 min – 45 min. The mixture was then
vacuum filtered to recover the lignin. The lignin was repeatedly washed with hot
water until all signs of foaming had subsided. It was then left to air-dry before
being further dried in a vacuum oven at 45°C overnight. This procedure
increases the purity of lignin by reducing the inclusion of ash and carbohydrate
components. It is different from other procedures reported in the literature
because it is based on a two-stage acid precipitation process. The initial
precipitation process at pH 5.5 produces lignin particles of high purity which are
then allowed to grow to larger sizes before proceeding to the second precipitation
stage where the proportion of impurities is highest.
Organosolv lignin (OL) was obtained through precipitation of the black liquor
into a dilute H2SO4 solution. The black liquor was obtained by the
delignification of bagasse at 190 oC with 50 wt% aqueous ethanol solution with a
liquor to solid ratio of 10:1, a reaction time of 90 min, in a 20 L Parr reactor.
Crude lignin was dissolved in 0.1 M NaOH equilibrated and precipitated with
H2SO4 at pH 3. The slurry was filtered hot and the residue was washed with
water until the filtrate became colourless. The lignin was air dried and further
dried at 45°C and 100°C, consecutively.
2.2.2. Lignin fractionation
Soda lignin is a complex and heterogeneous mixture with a rather broad
molecular weight distribution. Sequential fractionation was carried out to
separate the lignin into three fractions of distinct molecular weight/size and
chemical functionality. Ether and methanol are the solvents used in this study as
was used by Thring et al. (1996) to fractionate ALCELL lignin.
To fractionate soda lignin, ~ 100 g and 250 mL diethyl ether are added to a large
Schott bottle (1 L) or beaker (1 L). The container is covered and the contents are
then stirred for 20 min before being left to settle for 10 min. The diethyl ether is
49
then decanted into another container. The remaining solid is then subjected to
the same treatment. This is repeated until the supernatant diethyl ether is a light
yellow colour when decanted. The lignin residue is allowed to dry before this
process is repeated using methanol in place of ether. The diethyl ether fraction
(L1) and methanol fraction (L2) are either recovered using the rotary evaporator
to evaporate the solvent, or acid is used to precipitate the lignin, followed by
filtration to recover the solid lignin. All 3 fractions of lignin (L1, L2 and the
remaining residue, L3) are then dried and weighed. The moisture contents were
between 2.4 wt% and 3.8 wt%.
The OL was not fractionated in this study.
2.2.3. Lignin characterisation methods
2.2.3.1. Elemental analysis
Elemental analysis was performed on the lignin samples using a FLASHEA
1112 Elemental Analyser instrument. In preparing the samples for analysis, first
they were dried at 100°C overnight, to remove any moisture. To measure
carbon, hydrogen and nitrogen contents, 2 mg to 4 mg samples were
encapsulated in a tin container, and for measuring oxygen content 2 mg to 4 mg
samples were encapsulated in a silver container. The analysis results were
obtained via gas chromatography, and compared with those of standard
materials.
2.2.3.2. Ash analysis
Crucibles were pre-dried to constant weight in a muffle furnace at 575°C.
Lignin samples (0.5 g - 2 g) were weighed into the crucibles and heated to 105°C
to remove moisture. The crucibles were then heated at 575°C to constant weight.
The weight of ash remaining was calculated as a percentage of the original dry
weight of sample (Sluiter et al., 2008a). An internal reference bagasse material
in which the ash content is known was used as a standard.
2.2.3.3. Bulk density
The bulk density of the original lignin and L2 were determined using the
standard method (ASTM C29/C29M).
50
2.2.3.4. Sugar analysis
Analytical grade glucose was supplied by B.D.H. D- (+) Xylose and D- (+)
arabinose with purity > 99 wt% were supplied by Sigma. D-Cellobiose with
purity ≥ 99 wt% was supplied by Fluka. Standard stock solutions were prepared
with degassed deionised water. Analytical grade concentrated H2SO4 (98 wt%)
was supplied by Merck.
Aliquots of 3 mL of 72 wt% H2SO4 were added to 0.3 g samples of lignin in
pressure tubes. The tubes were placed in a water bath at 30°C for 1 h and stirred
intermittently to completely wet the lignin sample. The acid was then diluted to
4 wt% through the addition of water and the samples were autoclaved in pressure
tubes at 121°C for 1 h (Sluiter et al., 2008b). The samples were filtered through
porcelain crucibles to remove solids and the liquid fraction was analysed by high
performance liquid chromatography (HPLC) for glucose, xylose and arabinose.
The standard sugar solutions were also subjected to acid hydrolysis prior to
HPLC analysis in order to obtain the standard recoverable sugars.
2.2.3.5. Purity analysis
The purity of the lignin samples was calculated from the sum of ash and sugar
results. Due to the nature of the pulping and precipitation techniques, a
significant amount of ash and sugars may be present if the sample is not
copiously washed with distilled water.
2.2.3.6. Characterisation of functional groups
To predict the properties of lignin and its fractions, different functional group
analyses were performed. The functional groups quantified were the methoxyl
group, carboxylic acid functional group, phenolic hydroxyl group and total
hydroxyl group contents.
2.2.3.6.1. Methoxyl content method
The classical method for methoxyl determination of lignins uses hydroiodic acid
to promote demethylation and gas chromatography to determine the percentage
methoxyl content (Girardin and Metche., 1983). A less tedious method involves
the use of proton nuclear magnetic resonance (1H NMR) (Aberu and Freire,
1995).
51
The 1H NMR spectra of samples of acetylated lignins show that syringyl proton
signals occur between 6.28 ppm and 6.80 ppm, while the guaiacyl proton signals
occur between 6.80 ppm and 8.00 ppm. The theoretical ratios between aromatic
and methoxyl protons of guaiacyl and syringyl are 1.00 ppm and 0.33 ppm
respectively. These ratios can actually be measured from the 1H NMR spectra of
acetylated lignins. i.e. x = H(aromatic)/H(methoxyl). Aberu and Freir (1995)
analysed the 1H NMR spectra data of a whole range of acetylated lignins
(aromatic and methoxyl protons occur between 6.4 ppm to 7.1 ppm and 3.5 ppm
to 4.1 ppm respectively, see Figure 2-1) and plotted the ratio x against the %
methoxyl (OCH3) content obtained by the classical hydroiodic acid method for
the same lignins. They then submitted the data to a statistical linear regression
analysis to obtain equation (2-1):
% OCH3 = 28.28436 – 19.750047x (2-1)
For this study, soda lignin samples (~ 1 g) were added to mixtures of
pyridine/acetic anhydride (2:1) and the solutions were stirred at room
temperature for seven days. At the end of this, for each mixture, the pyridine
was removed by rotary evaporation with the periodic addition of ethanol. The
residue was dissolved in a small volume of chloroform and the solution was
added drop-wise with stirring to 200 mL of diethyl ether. The precipitated
acetate was then filtered off on a glass frit and collected solid was dried in
vacuum at 40 oC. The acetylated lignins were then analysed by 1H NMR to
obtain x from which the % OCH3 was calculated from equation 2-1.
52
Figure 2-1 NMR spectrum of an acetylated lignin (L2) fraction
2.2.3.6.2. Carboxylic acids and phenolic hydroxyl groups method
Carboxyl groups are believed to be present in native lignin, in extremely low
concentrations. However, when native lignin is subjected to chemical or
biological treatments, carboxyl groups are frequently detected in significant
quantities. Therefore, quantitative measurements of carboxyl groups may
provide information regarding the degree to which the lignin has been degraded
or modified as a result of treatment.
A titration method was used in this work (Dence, 1992). The saturated KCl
electrolyte generally used in calomel electrodes was replaced by a 1 M aqueous
solution of tetra-n-butylammonium chloride (TnBACl). The titrant (0.05M
TnBAH) was standardised through titration of benzoic acid in N,N’
dimethylformamide (DMF) to a sharp inflection break.
The lignin sample and p-hydroxybenzoic acid were dissolved in a solution of
distilled water, concentrated HCl and DMF. The solution was then titrated with
0.05 M TnBAH. There were three inflections in the titration curve. These
53
correspond to: excess HCl and strong acids present in the sample, carboxylic
acids, and phenolic hydroxyl groups, respectively.
A blank was also run on a solution of p-hydroxybenzoic acid, distilled water,
HCl and DMF.
2.2.3.6.3. Total hydroxyl groups by acetylation method
The amount of total hydroxyl group in lignin was determined by potentiometry
(Gosselink et al., 2004). The acetylation procedure given by Gosselink and co-
workers (2004) is known to be unreliable because the acetylation of lignin is not
complete. Therefore the procedure was slightly modified and the heating time
extended from 1 h to 24 h. Approximately 0.5 g - 0.8 g of air-dried lignin was
added to 10 mL of an acetic anhydride: pyridine (1:4 v/v) mixture. This was
heated overnight in an oil bath at 90°C. After adding 2 mL water and 5 min
stirring, 50 mL ethanol was added. Subsequently, the acetylated lignin was
potentiometrically titrated with a standardised 0.1 M NaOH in ethanol.
2.2.3.7. Molecular weight determination
As lignin from different crops or treatments can be extremely diverse in
structure, it is necessary to determine these differences through analytical
methods. The molecular weight of a polymer can be a good indication of its
strength as well as other physical properties. Size exclusion chromatography is a
simple technique that can be utilized to determine the molecular weight of lignin.
Lignin samples were prepared in eluent (0.1M NaOH) at 0.2 mg.mL-1 just prior
to analysis and filtered through a 0.45 µm syringe filter before running. Sodium
polystyrene sulfonate standards of molecular weights 4,950 g mol-1, 16,600 g
mol-1, 57,500 g mol-1, 127,000 g mol-1, 505,100 g mol-1 and 1,188,400 g mol-1
used to prepare a standard calibration curve. Lignin weight average molecular
weight (Mw) and number average molecular weight (Mn) were calculated using
the equation obtained from the trend line of the standard curve.
2.2.3.8. Thermogravimetric analysis (TGA)
Approximately 10 mg of sample was weighed into an aluminium pan and placed
in the thermogravimetric analyser (TGA). Heating was at a rate of 10°C min-1
and was performed from room temperature to approximately 800°C. The test
was performed in an atmosphere of nitrogen, which was injected at a flow rate of
54
15 mL min-1. A curve of weight loss against temperature was constructed from
the data obtained by the instrument. A derivative of this curve (dTG) was
produced to indicate the temperatures at which maximum rates of weight loss
occurred.
2.2.3.9. Differential scanning calorimetry (DSC)
Approximately 10 mg - 15 mg of lignin was precisely weighed and then
encapsulated in an aluminium pan. The pan was then placed in a DSC-Q100
instrument and heated from 0°C to 200°C at a heating rate of 10°C min-1 (cycle
1). The test was performed in an atmosphere of nitrogen, which was injected at a
flow rate of 15 mL min-1. Samples were then cooled at a rate of
30°C min-1, to -10°C (cycle 2). Samples were then reheated to 200°C at a rate of
10°C min-1 (cycle 3). The plot obtained from this second heating run shows the
Tg as a step transition.
2.3. Resul ts
2.3.1. The fractionation process
Only a very small portion of the original lignin sample, ~8 wt%, was recovered
using diethyl ether (L1). The major proportion, ~ 68 wt% is methanol soluble
(L2), and the residue makes up the remaining 24 wt% (L3). Similar fractional
yields (within 1 wt%) were obtained in repeat experiments, demonstrating the
reproducibility of the fractionation procedure. The results clearly show that
bagasse soda lignin is heterogeneous. For OL, values of 24 wt% for L1, 50 wt%
for L2 and 23 wt% for L3 were obtained. Thring et al. (1996) using a similar
fractionation procedure obtained values of 27 wt% for L1, 53 wt% for L2 and 18
wt% for L3 for an ALCELL lignin extracted from mixed hardwood. Based
solely on the fractionation data, it appears that the organosolv or ALCELL lignin
is more polydispersed than the soda lignin produced in this project.
2.3.2. Elemental analysis results
The elemental analysis results of the lignins are shown in Table 2-1. The data
show that carbon and hydrogen contents decrease from L1 to L3. The nitrogen
contents of the soda lignin and its fractions are lower than that of OL. The
55
protein contents in the soda lignin are in the range 0.13 wt% to 2.13 wt% if a
conversion factor of 6.26 is used. The protein content is low in the soda lignins
because proteins are soluble in alkali and so will easily be removed during the
lignin recovery process.
Tab le 2 - 1 E lementa l ana lys i s o f l i gn in s (wt %)
Sample N C H O
Starting lignin 0.29 63.25 5.95 26.40
L1 0.02 70.38 7.27 21.52
L2 0.26 63.83 6.00 27.47
L3 0.34 43.85 5.10 31.39
OL 0.50 62.10 6.20 29.00
Atomic ratios are calculated using values in Table 2-1, neglecting the nitrogen
contents, to give the empirical formulae of the different lignins (Table 2-2). In
lignin chemistry the empirical formula of the macromolecule is commonly given
as a hypothetical hydroxyphenyl structural unit (Quideau and Ralph, 1992). This
is known as the C9-formula, with six carbon atoms in the benzene ring plus three
carbon atoms making up the propyl side-chain. The results are shown in Table 2-
2. Worth noting, though not surprising, is that the C9 formula of L2 is similar to
that of OL.
Tab le 2 - 2 L ign in f rac t ion s fo rmu lae
Sample Empirical formula C9 formula
Starting lignin C5.27H5.95O1.65 C9H10.16O2.82
L1 C5.87H7.27O1.35 C9H11.15O2.07
L2 C5.32H6.00O1.72 C9H10.15O2.91
L3 C3.65H5.10O1.96 C9H12.58O4.83
OL C5.18H6.18O1.78 C9H10.73O3.15
2.3.3. Molecular weight and functional groups
The results of Size Exclusion Chromatography of soda lignin and three different
fractions is shown in Figure 2-2. In this figure, the intensity of UV absorbance
56
according to the retention time, for different fractions of lignin compared with
soda lignin, is shown.
Figure 2-2 Size exclusion chromatograms of lignin and its fractions
Table 2-3 shows Mn and Mw results of the soda lignins and OL. The molecular
weight of the soda lignins increases from L1 to L3. For these lignins, their
polydispersity are similar, with values around 1.1. This indicates that each
fraction essentially contains lignin of the same chain length. On the other hand,
Vanderlaan and Thiring (1998) obtained values of 1.5 for ether soluble fraction
and 2.3 for methanol fraction from ALCELL lignin.
As shown in Table 2-3, the methoxyl content of the OL is higher than that of the
soda lignins. This means that for bagasse, lignin is demethoxylated to a greater
extent during the soda extraction process (Thring et al., 1996) compared to the
organosolv process.
The methoxyl group content of the soda lignin fractions increases with molecular
weight. This increase is not related to molecular weight but related to the
insolubility of syringyl dominated lignin macromolecule in the ether and
methanol solvents used in the sequential fractionation process (Thring et al.,
1996). The results are also suggestive that the syringyl units are more difficult to
depolymerise during the delignification process.
57
Tab le 2 - 3 Molecu la r we ig h t ave rages and funct ion g roup s
Sample Mn
(g mol-1)
Mw
(g mol-1)
Mw/Mn Methoxyl*
(wt%)
Phenolic OH*
(wt%)
RCOOH*
(wt%)
Total OH*
(wt%)
Starting
lignin
2160 2410 1.12 10.9 5.1 13.6 14.5
L1 500 560 1.12 3.1 4.3 33.8 27.4
L2 2 380 2 670 1.12 11.7 1.5 21.1 15.3
L3 5 350 5 990 1.12 12.5 3.4 6.2 7.3
OL 2 000 2 300 1.15 15.1
* Error in analysis (% ±5)
The differences between the phenolic hydroxyl and the aliphatic hydroxyl for the
various soda fractions are due to the differences in polarity between ether and
methanol. The hydroxyl and carboxylic acid contents were highest with the
ether-soluble L1. Soda pulping generally increases the carboxylic acid contents
of lignins relative to organosolv pulping (Gosselink et al., 2004).
2.3.4. Sugar analysis results
The sugar and ash contents of lignin and its fractions are shown in Table 2-4.
The purity of the original soda lignin, L1 and L2 are comparable to OL. The low
purity of L3 is related to the high ash, xylan and glucan values. As xylan is
present in all the lignin samples, it confirms its strong association with the
phenolic backbone.
Mass balance calculations indicate that the ash content obtained for L3 cannot be
more than 9 wt%. The procedure used in the determination of the ash content of
lignin is based on heating the acid insoluble residue sample at 575°C to a
constant weight. If there is char formation of the carbohydrate residue during the
heating process, the value of the ash that is recorded will be inflated. Sample L3
has very high carbohydrate content (see Table 2-4) and it is therefore proposed
that there was char formation during heating at 575°C.
Energy dispersive spectroscopy indicated that the main element in the ashed
lignin samples is silicon. This is expected since sugarcane bagasse (from which
58
the lignins were extracted) contains high silica content. Minor amounts of
sodium, iron and potassium were also detected.
Tab le 2 - 4 Pu ri t y o f l i gn in s
Sample Ash
(wt %)
Glucan*
(wt %)
Xylan*
(wt %)
Arabinan*
(wt %)
Purity
(wt %)
Starting lignin 2.0 0.2 1.6 <0.1 96.3
L1 0.2 0.0 0.2 <0.1 99.6
L2 1.0 0.1 0.5 <0.1 98.4
L3 18.5 3.9 10.0 0.37 67.2
OL 0.4 1.4 0.6 <0.1 97.6
* Error in analysis (% ±2)
2.3.5. Bulk density results
The bulk density for the starting soda lignin was 680 kg m-3 and that for L2 was
640 kg m-3. These values are higher values than typically reported for soda
lignins which are between 450 kg m-3 and 500 kg m-3.
2.3.6. TGA results
The results for the thermal decomposition of soda lignin, soda lignin fractions
(i.e. L1, L2 and L3), and OL are in Figures 2-3 – 2-6. The decomposition
profiles of L2 and the starting lignin material are similar, supporting the solvent
fractionation result in which L2 constitutes the largest proportion of the starting
material. The TGA/dTG curves of all the samples predominantly show a two-
step (neglecting water loss) thermal decomposition process, though L2, L3 and
the starting lignin material in addition, have shoulders at higher temperatures.
The first weight loss starting from <100°C for L1 and at later temperatures for
the other lignins is associated with water loss. The second weight loss (i.e. the
first decomposition stage) with a peak temperature of 300–310°C is usually
assigned to the decomposition of hemicellulose (i.e. xylan) present in a
lignocellulosic matrix (Garcìa-Pèreza et al. 2001). The second stage
59
decomposition (peak temperature > 336– 367°C) is due to cellulose (i.e. glucan)
and lignin decomposition (Garcìa-Pèreza et al. 2001).
The weight loss recorded for L1 between 175°C and 310°C is 24 wt% (see
Figure 2-3). This weight loss cannot be associated with hemicellulose
decomposition because from the sugar analysis results of Table 3, the
hemicellulose (.i.e. xylan) content is 0.2 wt%. It is therefore likely that there is a
compound or compounds present in L1 that decompose in the temperature
regions associated with hemicellulose decomposition. This low molecular
weight compound or compounds may be polyphenolic in nature with a high
carboxylic acid content (see Table 2-4).
The maximum decomposition temperature of L1 is 380°C. For L2, L3 and the
starting lignin material, although 75 wt% of the material decomposes at
temperatures lower than 380°C, 25 wt% decomposes at temperatures > 400°C.
In summary, the TGA results clearly show that L1 is different from the other
lignin fractions. More importantly, the TGA results show that soda lignin is
thermally stable around 175°C, and so in preparing thermoplastics and polymer
blends with soda lignin, the working temperatures should be restricted to this
temperature region.
Figure 2-3 TGA/DTG curve of L1 performed under nitrogen atmosphere
60
Figure 2-4 TGA/DTG curve of L2 performed under nitrogen atmosphere
Figure 2-5 TGA/DTG curve of L3 performed under nitrogen atmosphere
61
Figure 2-6 TGA/DTG curve of the starting soda lignin performed under
nitrogen atmosphere
2.3.7. Glass transition temperature
The DSC results for cycle 3 for the soda lignins, as well as OL, are shown in
Figure 2-7. The results were processed using “Universal 4.2E TA” software.
Table 2-5 shows the Tg of the lignins. It shows that the Tg of the soda lignins
increased with increase in molecular weight, and that OL has the same Tg as L2.
The low Tg obtained with L1 suggests that it is not lignin but a related
polyphenolic macromolecule.
Figure 2-7 DSC curves for lignin and its fractions
62
Tab le 2 - 5 Tg o f l i gn in and f ra c t ion s
Sample Tg (°C)
Starting lignin 130
L1 51
L2 130
L3 154
OL 130
2.4. Discuss ion The results of this work have confirmed the heterogeneity that exists in soda
lignin. The lignin fractions obtained via sequential extraction were different in
carboxylic acid, methoxy, phenol hydroxyl, ash and sugar contents, as well as in
molecular weight. There is some similarity in the molecular weight averages
between the soda fraction obtained with methanol i.e. L2 and the organosolv
lignin, OL.
The high purity of L1 and L2 suggests that they can be used in similar
applications as organosolv lignin.
The highest phenolic hydroxyl group content, L1, has the highest potential to
react with oxyalkylating modification reagents such as ethylene oxide and
propylene oxide. This would improve the compatibility between lignin and
polyolefins and improve the dispersion of lignin in the polyolefin network. Also,
with the lowest methoxy content, L1 is likely posseses vacant sites that are
desirable for lignin functionalisation.
In the work reported by Muller et al. (1984) it was found that kraft lignin-based
phenol formaldehyde (PF) resins have superior properties to steam exploded
lignin-based PF resin. The differences were attributed to differences in the
chemical structure between the two lignin types. Kraft lignin was found to have
a higher phenolic guaiacyl content, lower carbon-carbon bonding between
aromatic rings, higher solubility in sodium hydroxide and higher molecular
weight than steam exploded lignin (Muller et al., 1984). So, to a certain degree,
63
the high phenolic content of the starting soda lignin material, L1 and L2 should
translate into good reactivity with formaldehyde in PF and epoxy resins.
Fraction L3, though high in ash content, will also be suitable for making PF
resins because of its relatively high molecular weight and high sugar content (i.e.
glucan and xylan).
For lignin to be used in free radical polymerisation reactions and for the
syntheses of acrylic resins and paints, its solubility can be improved in
monomers such as styrene and methyl methacryalate by reacting its hydroxyl
groups with acid anhydrides. Also its free radical scavenging ability would be
considerably reduced by the formation of a lignin ester. As fractions L1 and L2
are high in phenolic hydroxyl groups they will be expected to readily form the
desired ester, and because they contain a high percentage of carboxylic acid
functional groups they have a greater probability of increasing the elastic
character acrylic resins/paints through hydrogen-bond structuring.
64
2.5. References Aberu, H.D.S., Freire, M.D.F.I., 1995. Methoxyl content determination of lignins
by 1H NMR. An. Bras. Ci. 67, 379–382. Adler, E., 1980. Lignin chemistry-past, present, and future. Wood Sci. Technol.
14, 241–268. Chen, C.L., 1991. Lignins: occurrence in woody tissues, isolation, reactions, and
structure. Int. Fiber Sci. Technol. Ser. 11, 183–261. Dence, C.W., 1992. Determination of carboxylic groups. In: Lin, S.Y., Dence,
C.W. (Eds.), Methods in Lignin Chemistry. Springer, Berlin, pp. 458–464. Ede, R.M., Kilpelaeinen, I., 1995. Homo- and hetero-nuclear 2D NMR
techniques: unambiguous structural probes for non-cyclic benzyl aryl ethers in soluble ligninsamples. Res. Chem. Intermediates 21 (35), 313–328.
Food and Agriculture Organisation, 2009. Methods in lignin Chemistry. Prod STAT database. http://faostat.fao.org/site/567/DesktopDefault.aspx?PageID=567 #ancor.
Garcìa-Pèreza, M., Chaala, A., Yanga, J., Roy, C., 2001. Co-pyrolysis of sugarcane bagasse with petroleum residue. Part I: thermogravimetric analysis. Fuel 80.
Girardin, M., Metche, M., 1983. Microdosage rapide des groupements alkoxyles par chromatographie en phase gazeuse: application à la lignine. J. Chromatogr. A264, 155–158.
Gosselink, R.J.A., Abächerli, A., Semke, H., Malherbe, R., Käuper, P., Nadif, A., van Dam, J.E.G., 2004. Analytical protocols for characterisation of sulphur-free lignin. Ind. Crops Prod. 19 (3), 271–281.
Karhunren, P., Rummakko, P., Sipila, J., Brunow, G., 1995a. Dibenzodioxocin a novel type of linkage in softwood lignins. Tetrahedron Lett. 36 (1), 169– 170.
Karhunren, P., Rummakko, P., Brunow, G., 1995b. The formation of dibenzodioxocin structures by oxidative coupling. Amodel reaction for lignin biosynthesis. Tetrahedron Lett. 36 (25), 4501–4504.
Moerck, R., Yoshida, H., Kringstand, K.P., Hatakeyama, H., 1986. Fractionation of kraft lignin by successive extraction with organic solvents, 1. Functional groups, 13C-NMR-spectra and molecular weight distributions. Holzforschung 40, 51–60.
Muller, P.C., Kelley, S.S., Glasser, W.G., 1984. Engineering plastics from lignin. IX. Phenolic resin synthesis and characterisation. J. Adhes. 17, 185– 206.
Quideau, S., Ralph, J., 1992. Facile large-scale synthesis of coniferyl, sinapyl, and p-coumaryl alcohol. J. Agric. Food Chem. 40, 1108-1110.
Robert, D.R., Bardet, M., Gellerstedt, G.r., Lindfors, E.L., 1984. Structural changes in lignin during kraft cooking part 3. On the structure of dissolved lignins. J. Wood Chem. Technol. 4 (3), 239–263.
Sjostrom, E., 1981. Wood Chemistry: Fundamentals and Applications. Academic Press, Orlando, pp. 68–82.
Sluiter, A.H.B., Ruiz, R., Scarlata, C. Sluiter, J., Templeton, D., 2008a. Determination of ash in biomass: Laboratory Analytical Procedure (LAP); NREL Report No. TP- 510-42622.
65
Sluiter, A.H.B., Ruiz, R., Scarlata, C., Sluiter, J., Templeton, D., Crocker, D., 2008b. Determination of Structural Carbohydrates and Lignin in Biomass Laboratory Analytical Procedure (LAP); NREL Report No. TP-510-42618.
Song, C., 2002. Fuel processing for low-temperature and high-temperature fuel cells—challenges, and opportunities for sustainable development in the 21st century. Catal. Today 77, 17–49.
Thring, R.W., Vanderlaan, M.N., Griffin, S.L., 1996. Fractionation of ALCELL lignin by sequential solvent extraction. Wood Chem. Technol. 1996 (2), 139–154.
Vanderlaan, M.N., Thring, R.W., 1998. Polyurethanes from Alcell® lignin fractions obtained by sequential solvent extraction. Biomass Bioenergy 14 (5–6), 525–531.
Wallberg, O., Jönsson, A.S., Wimmerstedt, R., 2003. Fractionation and concentration of kraft black liquor lignin with ultrafiltration. Desalination 154 (2), 187–199
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66
CHAPTER 3
Thermal stabil i ty and miscibil i ty of
poly(hydroxybutyrate) and soda l ignin
blends
Payam Mousaviouna, William O.S. Dohertya and Graeme A. Georgeb
a Sugar Research and Innovation, Centre for Tropical Crops and
Biocommodities, Queensland University of Technology, GPO Box 2434,
Brisbane, Australia. b School of Science and Technology, Queensland University of Technology,
GPO Box 2434, Brisbane, Australia.
Published in Industrial Crops and Products, Vol 32, Page 656, 2010.
67
Abstract- The thermal properties and miscibility of poly(hydroxybutyrate)
(PHB) and soda lignin blends were investigated by thermogravimetry analysis
(TGA), differential scanning calorimetry (DSC), scanning electron microscopy
(SEM) and Fourier transform infrared spectroscopy (FT-IR) over the entire range
of composition. Although the addition of soda lignin shifts the onset of PHB
decomposition to lower temperatures, the PHB/lignin blends are thermally more
stable than PHB over a wider temperature range. The thermal behaviour of these
blends as measured by TGA suggests compatibility for the blends containing up
to 40 wt% soda lignin. These results correlate well with the glass transition
temperature (Tg) data where a single Tg was obtained for these blends. At higher
lignin to PHB ratios, two Tgs depicting immiscibility were obtained. The infrared
data show that the miscibility of the blends containing up to 40 wt% soda lignin
is associated with specific hydrogen bonding interactions between the reactive
functional groups in lignin with the carbonyl groups of PHB.
3.1. I ntroduct ion The negative impact of petrochemical-based platform chemicals and industrial
commodities has led to the use of “green” materials to reduce greenhouse gas
and toxic emissions, reduce energy demand, and reduce the use of non-
renewable resources. As a consequence, there has been a focus on the use of
environmentally friendly natural polymers and biopolymers. These polymers
include cellulose, hemicellulose, lignin, starch, proteins, fats, polynucleotides,
glycolide/lactide-based linear aliphatic polyesters, non-glycolide/lactic linear
aliphatic polyesters and aliphatic and aromatic polycarbonates. Of particular
interest is a class of microbially produced polymers known as
polyhydroxyalkanoates (PHAs). PHAs serve as intracellular carbon and energy
storage materials for the algae and bacteria that produce them (Verhoogt et al.,
1994). Polyhydroxybutyrate (PHB) is a member of this class of polymers. PHB
is insoluble in many solvents and has good barrier properties towards water,
oxygen and carbon dioxide (Ghaffar, 2002). It is readily broken down, with the
aid of enzymes, to water and carbon dioxide. These properties combined with
PHB’s potential for sustainable usage, makes it a potential commodity material
in the packaging industry.
68
The reasons why the potential of PHB has not been fully fulfilled, apart from its
prohibitive cost, are its stiff and brittle nature and its thermal instability during
processing. The crystal structure and crystallisation conditions are responsible
for these thermo-mechanical properties. PHB undergoes secondary nucleation at
ambient temperature because of its low glass transition temperature (Tg) and it
possesses a low nucleation density resulting in the formation of large spherulites
(Barham and Keller, 1986). The spherulites contain crazes, and splitting occur
around the centre of these crazes, hence producing a significant structural weak
point (Mahendrasingam et al., 1995). PHB undergoes thermal degradation and
depolymerisation at temperatures close to its melting point and degradation is
further enhanced by high shear rates during melt processing and extrusion.
As a result of these limitations, research efforts have concentrated on modifying
PHB by (a) changing its bulk properties without changing its physical form, (b)
changing its microstructure, (c) making it more resistant to thermal degradation
(d) changing its chemical properties, (e) modifying its solubility so that less toxic
chemicals are used, (f) improving its processability, and (g) lowering production
costs without sacrificing properties. One approach to improve PHB’s properties
is through blending. Polymer blending is a less expensive way of producing
materials with desired properties. The literature contains several investigations
of blends of PHB and other polymers such as poly(ξ-caprolactone) (Antunes and
Felisberti, 2005), poly(vinylidene fluoride) (Chiu et al., 2001), poly(viny
alcohol), poly(lactic acid), poly(vinyl acetate), poly(vinylphenol), poly(DL-
lactide)-co-poly(ethylene glycol), and cellulose esters. These polymers,
depending on proportion, result in good miscibility with PHB. Many of these
compounds have been found to be miscible or partially miscible on the basis of
specific hydrogen-bonding interactions (Kuo et al., 2002, Kuo and Chang, 2001,
Sixun et al., 2003, Yong et al., 2001, Yoshie et al., 1995, Zheng and Mi, 2003).
The main factors affecting the miscibility of polymers are the chemical nature of
the polymer constituents and their molecular weight. The chemical nature of the
polymers accounts for the existence of strong interactions (i.e., negative
enthalpy) between the polymers. Thus, polymers with interacting functional
groups that result in hydrogen-bond formation and ionic interaction would
69
enhance miscibility between polymer systems (Viswanathan and Dadmun,
2002).
Lignin is an amorphous macromolecule composed of phenylpropane repeat units
and possesses aliphatic and aromatic hydroxyl groups as well as carboxylic acid
groups. These interacting functional groups, as well as its amorphous nature
make lignin a good candidate for blending with aliphatic polyesters, such as
PHB. The amorphous nature of lignin may reduce the formation of large
spherulites, retard crystallisation (Ghosh, 1998) and reduce secondary
nucleation, all of which impact on PHB brittleness. Limited studies have been
carried out on PHB and lignin blends. Ghosh (1998), Ghosh et al. (1999) and
Ghosh et al. (2000) prepared blends (from the melt and solution) of PHB,
polyhydroxybutyrate-hydroxyvalerate (PHBV) and cellulose acetate butyrate
with organosolv lignin and organosolv lignin ester. The organosolv lignin and
its butyrate derivative were found to have a high degree of miscibility with PHB,
and the lignin was found to inhibit and retard PHB crystallisation. Ghosh et al.
(2000b) reported that the Tg of the blends increased from that of pure PHB
towards that of lignin/lignin butyrate further confirming some compatibility
between PHB and lignin. The organosolv lignin used in these studies was
obtained through extraction of hardwood with aqueous ethanol. The source from
which lignin is obtained and the method of extraction has a strong bearing on its
properties (Lora and Glasser, 2002). Thus, in this work the miscibility between
PHB and soda lignin was examined using thermal and spectroscopic methods.
The soda lignin was obtained from sugarcane fibre (i.e. bagasse) with sodium
hydroxide as solvent used in the extraction process.
3.2. Mater ia ls and Methods
3.2.1. PHB
Bacterial PHB was obtained from Sigma Aldrich. The weight average molecular
weight, Mw as determined by gel permeation chromatography is 440,000 g mol-1
while the number average molecular weight, Mn is 260,000 g mol-1. The Tg of
the PHB is 4°C and the melting point is 173°C.
70
3.2.2. Soda lignin extraction
Bagasse was obtained from a Mackay Sugar Mill, Queensland, Australia. It was
wet depithed (through a 4.2 mm screen) and then air dried. Soda lignin was
extracted from bagasse by the soda process using a 20 L Parr reactor. In this
method, 1 kg of bagasse is reacted with about 10.5 L of 0.7 M - 1 M NaOH.
Once the reactor reached the operating temperature of 170°C, it was maintained
at that temperature for 1.5 h. After cooling, the liquid (black liquor) was
removed from the bottom of the reactor and sieved to remove fibrous material.
To the black liquor, dilute H2SO4 (0.1 M) was slowly added with stirring to pH
5.5. Near pH 5.5 an obvious change in the appearance of the solution occurs;
from black to murky brown. This change is due to the initial stages of lignin
precipitation. The mixture was stirred for 10 min - 15 min after which
acidification is continued to pH 3. It was then transferred to a 65°C water bath
and stirred using an overhead stirrer for 30 min – 45 min. The mixture was then
vacuum filtered to recover the soda lignin. The soda lignin was repeatedly
washed with hot water until all signs of foaming have subsided. It was then left
to air-dry before being further dried in a vacuum oven at 45°C overnight. This
procedure increases the purity of soda lignin by reducing the inclusion of ash and
carbohydrate components. It is different from other procedures reported in the
literature because it is based on a two-stage acid precipitation process. We posit
that the initial precipitation process at pH 5.5 produces lignin particles of high
purity which were then allowed to grow to larger sizes before proceeding to the
second precipitation stage where the proportion of impurities is highest. The
extraction process and recovery procedure resulted in the recovery of 89 wt% of
the starting lignin content (22.2 wt%) in the bagasse.
3.2.3. Lignin characterisation method
3.2.3.1. Elemental analysis
Elemental analysis was performed on the soda lignin sample using a FLASHEA
1112 Elemental analyser instrument. In preparing the sample for analysis it was
dried at 100°C overnight, to remove any moisture. To measure carbon, hydrogen
and nitrogen contents, 2 mg to 4 mg of sample was encapsulated in a tin
container, and for measuring oxygen content the same quantity of soda lignin
71
was encapsulated in a silver container. The results were obtained gas
chromatography, and compared with those of standard materials.
3.2.3.2. Ash analysis
Crucibles were pre-dried to constant weight in a muffle furnace at 575°C.
Lignin samples (0.5 g - 2 g) were weighed into the crucibles and heated to 105°C
to remove moisture. The crucibles were then heated at 575°C to constant weight.
The weight of ash remaining was calculated as a percentage of the original dry
weight of sample (Sluiter et al., 2008a). An internal reference bagasse material
in which the ash content is known was used as a standard.
3.2.3.3. Sugar analysis
Analytical grade glucose was supplied by B.D.H. D- (+) Xylose and D- (+)
arabinose with purity > 99 wt% were supplied by Sigma. D-Cellobiose with
purity ≥ 99 wt% was supplied by Fluka. Standard stock solutions were prepared
with degassed deionised water. Analytical grade concentrated H2SO4 (98 wt%)
was supplied by Merck.
Aliquots of 3 mL of 72 wt% H2SO4 were added to 0.3 g samples of soda lignin
in pressure tubes. The tubes were placed in a water bath at 30°C for 1 h and
stirred intermittently to completely wet the lignin sample. The acid was then
diluted to 4 wt% through the addition of water and the samples were autoclaved
in pressure tubes at 121°C for 1 h (Sluiter et al., 2008b). The samples were
filtered with porcelain crucibles to remove solids and the liquid fraction was
analysed by high performance liquid chromatography (HPLC) for glucose,
xylose and arabinose. This was performed on a Waters system equipped with a
Waters 590 pump and a Waters 410 RI detector. The HPLC configuration
included a Shodex KS-801 column with guard KS-G. The column was operated
at 85°C. The standard sugar solutions were also subjected to acid hydrolysis
prior to HPLC analysis in order to obtain the standard recoverable sugars.
3.2.3.4. Characterisation of functional groups
Lignin possesses different functional groups. The functional groups quantified
were the methoxyl group (Abreu and Freire, 1995), carboxylic acid (Dence,
1992), phenolic hydroxyl group (Dence, 1992) and total hydroxyl group contents
(Gosselink et al., 2004).
72
3.2.3.5. Molecular weight determination
The soda lignin sample was prepared in 0.1M NaOH eluent at 0.2 mg.mL-1 just
prior to analysis and filtered through a 0.45 µm syringe filter before running.
The analysis was performed on a Waters system equipped with a Waters 2487
UV detector set at 280 nm. The column used was a Shodex Asahipak GS-320
HQ with guard Asahipak GS-2G 7B. Sodium polystyrene sulfonate standards of
molecular weights 4,950 g mol-1, 16,600 g mol-1, 57,500 g mol-1, 127,000 g mol-
1, 505,100 g mol-1 and 1,188,400 g mol-1 used to prepare a standard calibration
curve. Lignin weight average molecular weight (Mw) and number average
molecular weight (Mn) were calculated using the equation obtained from the
trend line of the standard curve.
3.2.4. Blend preparation
Soda lignin and PHB were dried at 100°C and 40°C respectively, for 12 h and
then stored in desiccators under vacuum prior to use. Lignin-PHB blends with
lignin contents from 10 wt% to 90 wt% were mixed in a Haake mini lab twin
screw using the procedure reported by Ghaffar (2002). To minimise PHB
degradation, the temperature of the extruder was maintained at 175°C for 2 min.
The polymer blends were extruded as strands then cooled and pelletised. The
pellets were stored in a desiccator to avoid moisture absorption. Similar
processing conditions were carried out for soda lignin and PHB.
3.2.5. Characterisation of blend samples
3.2.5.1. Thermogravimetric analysis (TGA)
The thermal decomposition studies were carried out in a TA Instruments Q500.
Approximately 10 mg of sample was weighed into an aluminium pan and
analysed by thermogravimetric analysis (TGA). Heating was at a rate of 10°C
min-1 and was performed from room temperature to approximately 800°C. The
test was performed in an atmosphere of nitrogen, which was injected at a flow
rate of 15 mL min-1. A curve of weight loss against temperature was constructed
from the data obtained by the instrument. A derivative of this curve (DTG) was
produced to indicate the temperatures at which maximum rates of weight loss
occurred.
73
3.2.5.2. Differential scanning calorimetry (DSC)
Approximately 10 mg - 15 mg of sample was precisely weighed and then
encapsulated in an aluminium pan. The pan was then placed in a DSC-Q100
instrument and heated from 0°C to 200°C at a heating rate of 10°C min-1 (cycle
1). The test was performed in an atmosphere of nitrogen, which was injected at a
flow rate of 15 mL min-1. Samples were then cooled at a rate of
30°C min-1, to -10°C (cycle 2). Samples were then reheated to 200°C at a rate of
10°C min-1 (cycle 3). The plot obtained from this second heating run shows the
Tg as a step transition.
3.2.5.3. Scanning electron microscopy (SEM)
The morphology of the PHB/soda lignin blends was examined using a scanning
electron microscope, type FEI Quanta 200 Environmental SEM at an
accelerating voltage of 15 kV. For this examination the pellets were
compression moulded between two sheets of Teflon using an established
procedure (Ghosh et al., 1999).
3.2.5.4. Fourier transform-Infrared spectroscopy (FT-IR)
IR spectra were collected using a Nicolet 870 Nexus Fourier transform infrared
(FT-IR) spectrometer equipped with a Smart Endurance single bounce diamond
ATR accessory (Nicolet Instrument Corp., Madison, WI). Spectra were
manipulated and plotted with the use of the GRAMS/32 software package
(Galactic Corp., Salem, NH). The spectrometer incorporated a KBr beam splitter
and a deuterated triglycine sulfate room temperature detector. Spectra were
collected in the spectral range 4000 to 525 cm-1, using 64 scans at 4 cm-1
resolution with a mirror velocity of 0.6329 cm.s-1. The measurement time for
each spectrum was around 60 s.
3.3. Resul ts and D iscuss ion The molecular weight and the percentage composition of the soda lignin used in
this work is given in Table 3-1. The purity (determined from the sum of the ash
and sugars) is comparable to organosolv lignin obtained from a previous study in
our laboratory (Mousavioun and Doherty, 2010). The polydispersity (i.e. ratio of
Mw to Mn) of the soda lignin is 1.1 indicating that the lignin polymer consists of
molecules of similar chain length.
74
Tab le 3 - 1 Molecu la r we ig h t o f soda l i gn in and l ign in co mponent s (wt %)
Ash* Glucan* Xylan* Arabinan* Purity
2.0 0.2 1.6 <0.1 96.1
* Error in analysis (% ±2)
** Error in analysis (% ±5)
The integral thermogravimetric curves for PHB, soda lignin and PHB/soda lignin
blends are given in Figure 3-1. PHB appears to have two main overall
degradation steps while soda lignin degradation is complex constituting of
several processes (Mousavioun and Doherty, 2010). For PHB/soda lignin
blends, degradation occurs in several more stages (Figure 3-1) suggesting that
blending PHB with soda lignin completely changes the decomposition behaviour
of PHB. As shown in Figure 3-1, the decomposition temperature at which the
material has reached 5 wt% degradation (T0) of PHB decreases with the addition
of soda lignin. For example, T0 for pure PHB is 212°C, whereas it is 162°C for
PHB/lignin blend with a composition of 60/40. Also, the temperature at the
maximum rate of weight loss of PHB decreases with soda lignin addition (Figure
3-1). Whilst these results are suggestive that the addition of soda lignin
promotes PHB degradation, it does not, however, give a quantitative assessment
of the overall thermal stability of the blends. As shown in Figure 3-1,
degradation of pure PHB is almost complete by ~260°C, whereas the weight loss
for the blends at this temperature is less than 60 wt%. The lower weight loss is
an indication that the blends are thermally more stable than PHB over a wider
temperature range.
Mn
(g mol-1)
Mw
(g mol-1)
Methoxy**
Phenolic
OH**
RCOOH** Total
OH**
2160 2410 10.9 5.1 13.6 14.5
75
Figure 3-1 The integral thermogravimetric curves for PHB, soda lignin
and PHB/soda lignin blends. Lizymol and Thomas (1993) used TGA to study the thermal properties of
miscible and immiscible polymer blends. For the miscible poly(vinyl
chloride)/poly(ethylene–co-vinyl acetate) blends, they found that increasing the
proportion of poly(ethylene-co-vinyl acetate) in the blend effectively increased
T0 and the temperature at 50 wt% weight loss (T50) more than in proportion to
the proportion of poly(ethylene-co-vinyl acetate) in the blend. For the
immiscible, poly(ethylene-co-vinyl-acetate) / poly(styrene-co-acrylonitrile)
systems, the T0 values of the blends were lower than the proportion of
poly(ethylene-co-vinyl acetate) in the blend, while T50 values were virtually
unaffected. Based on this approach, plots of T0 and T50 of PHB/soda lignin
blends versus soda lignin content were constructed and the results are presented
in Figure 3-2.
76
Figure 3-2 Plots of T0 and T50 of PHB/soda lignin blends versus soda lignin
content. As the soda lignin content increases T0 decreases, but the decrease does not
correspond to the proportional amount of soda lignin added to the blend.
However, at low lignin contents (up to 20 wt%), T50 values increases more than
in proportion to the proportion of soda lignin added (i.e. well above the tie line)
possibly suggesting some degree of miscibility between soda lignin and PHB at
these compositions. At soda lignin concentrations > 20 wt%, the results may
suggest incompatibility between the components. As the PHB/soda lignin
systems are not similar to those of Lizymol and Thomas (1993), the results
shown in Figure 3-2 may simply be an indication of lignin degradation products
reacting with PHB degradation products to form stable species.
The most accepted parameter to assess polymer miscibility is the Tg. A single Tg
of a blend implies complete miscibility between the polymer pairs in their
amorphous fractions, whose value is an average of the individual component’s
Tg. Two or more Tg’s suggest that the degree of miscibility is restricted. Figure
3-3 shows the DSC curves of the blends where the Tgs were obtained using TA
Universal Analysis 2000 software. The exothermic peak at ~80°C (for 50 wt%
77
and 60 wt% lignin) is associated with cold crystallisation temperature of PHB.
Ghaffar (2002) obtained similar cold crystallisation temperatures for PHB and
polyvinyl acetate blends. Why the peak is prominent in some blends and not in
others is not known and is worth future investigation.
Figure 3-3 DSC curves of PHB/soda lignin. (refer to Figure 4-5) Most miscible polymers display a single Tg whose value is dependent on the
proportion of the individual components (Fox, 1956). Figure 3-4 illustrates the
Tgs of PHB and the blends. A single Tg is obtained up to a soda lignin content of
40 wt%, thereafter there are two Tgs. The error in the analysis is % ±5. The Tgs
results therefore give a further indication of miscibility between PHB and soda
lignin at soda lignin contents up to 40 wt%.
78
Figure 3-4 Tgs of PHB and the blends versus soda lignin content. Figure 3-3 also shows that the Tg of the PHB component of the blends increases
with increase in soda lignin content. Similar results were obtained by Ghosh and
co-workers (Ghosh et al., 1999, Ghosh et al., 2000) for organosolv lignin/PHB
blends, though the values obtained in the present study were slightly higher
(Figure 3-4). This could be related to the method of preparation, differences in
the PHB source, or the lignin type as soda pulping generally increases the
carboxylic acid and hydroxyl contents of lignins relative to organosolv pulping
(Gosselink et al., 2004).
To obtain a better idea of interactions between PHB and soda lignin, we
evaluated the Tg data using the well-known Fox, Gordon-Taylor and Kwei
equations. These are:
Fox equation: �Op7qi_@r8 2 sL
Op,L3 sM
Op,M (3-1)
Gordon-Taylor equation: 9t7qi_@r8 27u19w,13j-9u29w,28
7u13j-9u28 (3-2)
Kwei equation: 9t7qi_@r8 27u19w,13juu29w,28
7u13juu28 3 yu�uR (3-3)
where Tz,� {| R and w� {| R are glass transition temperatures of the pure
components and their corresponding weight fractions, respectively. K��, K� and
q are adjustable parameters. As can be seen in Figure 3-4, the PHB/soda lignin
79
blends up to 40 wt% lignin fit nicely to the Gordon-Taylor with a K�� value of
4.15. It also fitted the Kwei equation with K� value of 0.2 and q having a value
of 22. The positive value of q and a relatively high value of K�� (larger than 1)
indicate that strong interactions (ElMiloudi et al., 2009) exist between OH
groups of lignin and the carbonyl groups of PHB for the blends containing up to
40 wt% lignin.
Figures 3-5, 3-6 and 3-7 illustrate typical SEM images of blends. For blends of
PHB/soda lignin containing 10 wt% and 30 wt% lignin, there was no apparent
phase separation, whereas for the blend with a 50/50 composition in weight,
phase separation is observed. For other compositions higher than 50 wt% soda
lignin, phase separation between the components was detected. Thus, the SEM
data follow similar trends as the data obtained from the Tg of the blends.
Figure 3-5 SEM image of PHB/soda lignin containing 10 wt% lignin.
80
Figure 3-6 SEM image of PHB/soda lignin containing 30 wt% lignin.
Figure 3-7 SEM image of PHB/soda lignin containing 50 wt% lignin. Attempts at understanding the miscibility of the PHB/soda lignin blends have
been made using FT-IR, as have been undertaken by previous workers with
similar polymer systems (Dong and Ozaki, 1997). Infrared spectroscopy
provides information on hydrogen bond formation (and other interactions) and
the strength of H-bonds through wavenumber shift, band intensity and band
width of specific signals. Figure 3-8 shows the FT-IR spectra from 1800 cm-1 to
1620 cm-1 of the carbonyl stretching region of PHB and PHB/soda lignin blends.
The PHB spectrum exhibits two peaks, these are at ~1733 cm-1and ~1722 cm-1,
though the first peak at 1733 cm-1 is more of a shoulder to the main peak at 1722
cm-1. The peak at 1733 cm-1 is associated with the amorphous component of
PHB, the peak at ~1722 cm-1 is associated with the crystalline component of
81
PHB (in its preferred conformation). The band at 1685 cm-1 has been reported to
be a crystalline band, although its origin is not known (Guo et al. 2010).
Figure 3-8 FT-IR spectra of the carbonyl stretching region of PHB and
PHB/soda lignin blends. Figure 3-8 also shows that for blends containing 10, 20, 30, 40 and 50 wt% soda
lignin, there is a small but definite shift (2 cm-1 to 4 cm-1) to a lower
wavenumber for the main PHB peak. The shift to a lower wavenumber is
indicative of hydrogen bonding interactions because the stretching frequencies of
participating groups usually move towards lower wavenumbers (Barsbay and
Güner, 2007). Barsbay and Guner (2007) obtained similar small shifts for blends
of dextran and poly(ethylene glycol) cast in water. The present results therefore
indicate that the reactive functional groups of lignin are probably engaged in
hydrogen bonding interactions (or other associations) with the carbonyl oxygen
in PHB (Figure 3-9).
82
Figure 3-9 Hydrogen bonding interactions between the reactive functional
groups in soda lignin and the carbonyl groups of PHB. It is not known why there were no differences in the wavenumber shifts between
these blends containing different proportions of lignin. Figure 3-8 also shows
that there are no shifts observables for PHB blends containing 60 wt% to 90 wt%
of lignin relative to the PHB band at 1724 cm-1, thereby confirming previous
observations concerning the immiscibility of PHB/lignin blends containing these
compositions. It should however, be noted (as shown in Figure 3-8), that there
are noticeable shifts to lower wavenumbers for all the blends for the PHB band
at1742 cm-1. Since this band is of far less intensity compared to the main band at
1722 cm-1, and consequently is less prominent, it may be concluded that there are
some favourable weak interactions between the amorphous part of PHB and
lignin at all lignin proportions.
3.4. Conclus ion Soda lignin was found to improve the overall thermal stability of PHB, though it
reduced the initial temperature of decomposition of PHB. The TGA, DSC and
SEM of the PHB/soda lignin blends suggest that intermolecular interactions
between PHB and soda lignin were favoured at a soda lignin content of up to 40
wt%. These intermolecular interactions were found to be due to hydrogen
83
bonding formation between the reactive functional groups of lignin and the
carbonyl groups of PHB.
Acknowledgments Many thanks go to Dr Llew Rintoul of the School of Physical and Chemical
Sciences and Dr Lalehvash Moghaddam of Sugar Research and Innovation,
Centre for Tropical Crops and Biocommodities both at Queensland University of
Technology, Brisbane, Australia for their assistance in FT-IR analysis.
84
3.5. References Abreu, H.D.S., Freire, M.D.F.I., 1995. Methoxyl content determination of lignins
by 1H NMR. Ann. Acad. Bras. Cienc. 67, 379–382.
Antunes, M.C.M., Felisberti, M.I., 2005. Blends of poly(hydroxybutyrate) and poly(ecaprolactone) obtained from melting mixture. Polym. Sci. Technol. 15, 134–138.
Barham, P.J., Keller, A., 1986. The relationship between microstructure and mode of fracture in polyhydroxybutyrate. J. Polym. Sci. Part B: Polym. Phys. 24, 69–77.
Barsbay, M., Güner, A., 2007. Miscibility of dextran and poly(ethylene glycol) in solid state: Effect of the solvent choice. Carbohyd. Polym. 69, 214–223.
Chiu, H.J., Chen, H.L., Lin, J.S., 2001. Crystallization induced microstructure of crystalline/crystalline poly(vinylidenefluoride)/poly(3-hydroxybutyrate) blends probed by small angle X-ray scattering. Polymer 42, 5749–5754.
Dence, C.W., 1992. Determination of carboxyl groups by non-aqueous potentiometric titration. In: Lin, S.Y., Dence, C.W. (Eds.), Methods in Lignin Chemistry. Springer, Berlin, Heidelberg, pp. 458–464.
Dong, J., Ozaki, Y., 1997. FT-IR and FT-Raman studies of partially miscible poly(methyl methacrylate)/poly(4-vinylphenol) blends in solid states. Macromolecules 30, 286–292.
ElMiloudi, K., Djadoun, S., Sbirrazzuoli, N., Geribaldi, S., 2009. Miscibility and phase behaviour of binary and ternary homoblends of poly(styrene-coacrylic acid), poly(styrene-co-N,N-dimethylacrylamide) and poly(styrene-co-4- vinylpyridine). Thermochim. Acta 483, 49–54.
Fox, T.G., 1956. Influence of diluent and of copolymer composition on the glass temperature of a polymer system. Bull. Am. Phys. Soc. 2, 123.
Ghaffar, A.M.E.A., 2002. Development of a biodegradable material based on Poly(3- hydroxybutyrate) PHB. Ph.D. Thesis, Martin-Luther University, Wittenberg, Germany.
Ghosh, I., 1998. Blends of biodegradable thermoplastics with lignin esters. M.Sc. Thesis, Virginia Polytechnic Institute and State University, VA, USA.
Ghosh, I., Jain, R.K., Glasser, W.G., 1999. Multiphase materials with lignin. XV. Blends of cellulose acetate butyrate with lignin esters. J. Appl. Polym. Sci. 74, 448–457.
Ghosh, I., Jain, R.K., Glasser, W.G., 2000a. Blends of biodegradable thermoplastics with lignin esters. In: Glasser, W.G., Northey, R.A., Schultz, T.P. (Eds.), Lignin: Historical, Biological, and Materials Perspectives. American Chemical Society, Washington, DC, pp. 331–350.
Ghosh, I., Jain, R.K., Glasser, W.G., 2000b. Multiphase materials with lignin. Part 16. Blends of biodegradable thermoplastics with lignin esters. ACS Symp. Ser. 742, 331–350.
85
Gosselink, R.J.A., Abächerli, A., Semke, H., Malherbe, R., Käuper, P., Nadif, A., van Dam, J.E.G., 2004. Analytical protocols for characterisation of sulphur-free lignin. Ind. Crops Prod. 19, 271–281.
Guo, L., Sato, H., Hashimoto, T., Ozaki, Y., 2010. FT-IR study on hydrogen-bonding interactions in biodegradable polymer blends of poly(3-hydroxybutyrate) and pol(4-vinylphenol). Macromolecules 43, 3897–3907.
Kuo, S.W., Chang, F.C., 2001. Effects of copolymer composition and free volume change on the miscibility of poly(styrene-co-vinylphenol) with poly(ɛ- caprolactone). Macromolecules 34, 7737–7743.
Kuo, S.W., Chan, S.C., Chang, F.C., 2002. Miscibility enhancement on the immiscible binary blend of poly(vinyl acetate) and poly(vinyl pyrrolidone) with bisphenol A. Polymer 43, 3653–3660.
Lizymol, P.P., Thomas, S., 1993. Thermal behaviour of polymer blends: a comparison of the thermal properties of miscible and immiscible systems. Polym. Degrad. Stab. 41, 59–64.
Lora, J.H., Glasser, W.G., 2002. Recent industrial applications of lignin: a sustainable alternative to nonrenewable materials. J. Polym. Environ. 10, 39–48.
Mahendrasingam, A., Martin, C., Fuller, W., Blundell, D.J., MacKerron, D., Rule, R.J., Oldman, R.J., Liggat, J., Riekel, C., Engstrom, P., 1995. Microfocus X-ray diffraction of spherulites of poly-3-hydroxybutyrate. J. Synchr. Rad. 2, 308–312.
Mousavioun, P., Doherty, W.O.S., 2010. Chemical and thermal properties of fractionated bagasse soda lignin. Ind. Crops Prod. 31, 52–58.
Sixun, Z., Qipeng, G., Chi-Ming, C., 2003. Epoxy resin/poly(ɛ-caprolactone) blends cured with 2,2-bis[4-(4-aminophenoxy)phenyl]propane. II. Studies by Fourier transform infrared and carbon-13 cross-polarization/magic-angle spinning nuclear magnetic resonance spectroscopy. J. Polym. Sci., Part B: Polym. Phys. 41, 1099–1111.
Sluiter, A., Hames, B., Ruiz, R., Scarlata, C., Sluiter, J., Templeton, D., 2008a. Determination of Ash in Biomass. Laboratory Analytical Procedure (LAP).
Sluiter, A., Hames, B., Ruiz, R., Scarlata, C., Sluiter, J., Templeton, D., Crocker, D., 2008b. Determination of Structural Carbohydrates and Lignin in Biomass. Laboratory Analytical Procedure (LAP).
Verhoogt, H., Ramsay, B.A., Favis, B.D., 1994. Polymer blends containing poly(3-hydroxyalkanoate)s. Polymer 35, 5155–5169.
Viswanathan, S., Dadmun, M.D., 2002. Guidelines to creating a true molecular composite: inducing miscibility in blends by optimizing intermolecular hydrogen bonding. Macromolecules 35, 5049–5060.
Yong, H., Naoki, A., Yoshio, I., 2001. Blend of poly(ɛ-caprolactone) and 4,4’-thiodiphenol: hydrogen bond formation and some solid properties. Macromolecules Chem. Phys. 202, 1035–1043.
Yoshie, N., Azuma, Y., Sakurai, M., Inoue, Y., 1995. Crystallization and compatibility of poly(vinyl alcohol)/poly(3-hydroxybutyrate) blends:
86
influence of blend composition and tacticity of poly(vinyl alcohol). J. Appl. Polym. Sci. 56, 17–24.
Zheng, S., Mi, Y., 2003. Miscibility and intermolecular specific interactions in blends of poly(hydroxyether of bisphenol A) and poly(4-vinyl pyridine). Polymer 44, 1067–1074.
87
CHAPTER 4
Thermophysical properties and
rheology of PHB/lignin blends
Payam Mousaviouna, Peter Halleyb and William O.S. Dohertya a Sugar Research and Innovation, Centre for Tropical Crops and
Biocommodities, Queensland University of Technology, GPO Box 2434,
Brisbane, Australia. b Centre High Performance Polymers (CHPP), School of Chemical Engineering
and AIBN, St Lucia, The University of Queensland, QLD 4072, Brisbane,
Australia
Submitted to the Polymer International, 2011
Research Students Centre, Level 4, 88 Musk Avenue, Kelvin Grove Campus, GPO Box 2434. Brisbane QLD 4001
Ph: +61 7 3138 4475 or 3138 5306 e-mail [email protected] http://www.rsc.qut.edu.au/studentsstaff/
Correct as at: 7-6-10
Suggested Statement of Contribution of Co-Authors for
Thesis by Published Paper The authors listed below have certified* that: 1. they meet the criteria for authorship in that they have participated in the conception,
execution, or interpretation, of at least that part of the publication in their field of expertise;
2. they take public responsibility for their part of the publication, except for the responsible author who accepts overall responsibility for the publication;
3. there are no other authors of the publication according to these criteria; 4. potential conflicts of interest have been disclosed to (a) granting bodies, (b) the
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In the case of this chapter: Publication title and date of publication or status: “Value-adding to cellulosic ethanol: Lignin polymers”, published in Industrial Crops and Products, Vol 33, 259-276, 2011.
Contributor Statement of contribution* Payam
Mousavioun Collating of literature. Signature
Date William
O.S.Doherty Wrote the manuscript.
Christopher M.Fellows Edited and wrote some sections of the manuscript.
Principal Supervisor Confirmation I have sighted email or other correspondence from all Co-authors confirming their certifying authorship. _______________________ ____________________ ______________________ Name Signature Date
88
Abstract- The thermal and rheological properties of poly(hydroxybutyrate)
(PHB) and lignin blends were investigated by thermogravimetry analysis (TGA),
differential scanning calorimetry and rheology over the entire range of
composition. Although the addition of lignin shifts the onset of PHB
decomposition to lower temperatures, the PHB/lignin blends are thermally more
stable in terms of overall weight loss at temperature than PHB over a wider
temperature range. However, the drop in the apparent energy of activation of
decomposition, E� from 112 kJ mol-1 for pure PHB to half that value with
blends, in fact suggests that lignin reduces the thermal stability of PHB and that
the reduced weight loss observed in the TGA curves is associated with the
slower rate of degradation of lignin. The rheology results show that for 10 wt%
and 30 wt% lignin, lignin behaved like a plasticizer forming a single phase with
PHB and reduced the elasticity and viscosity relative to pure PHB. For further
additions of lignin (60 wt% and 90 wt% lignin), lignin then acts as a second
phase and decreased the ability of the system to dissipate energy and increased
the viscosity of the blends. These results are in good agreement with the glass
transition data, showing that critical changes in phase behaviour are dependent
on material composition.
4.1. I ntroduct ion There are concerted efforts to produce biodegradable polymers as alternatives to
the petroleum-based ones. Polyhydroxybutyrate (PHB) and similar bacterial
polyesters have obtained world-wide interest because of their biodegradability,
sustainability, and their durability and plasticity. PHB has remarkably similar
properties to those of PP, but is expensive, stiff and brittle in nature, and is
thermally unstable during processing. The crystal structure and crystallisation
behaviour are responsible for these thermo-mechanical properties. As a
consequence of these properties, polymer blending has been used to try to
modify PHB and improve its properties and lower production costs. Literature
contains several investigations of blends of PHB and other polymers such as
poly(ξ-caprolactone) (Antunes and Felisberti, 2005), poly(vinylidene fluoride)
(Chiu et al., 2001), poly(viny alcohol) (Yoshie et al., 1995), poly(lactic acid)
89
(Zhang et al., 1997), poly(vinyl acetate) (An et al., 1997), poly(vinylphenol)
(Xing et al., 1997), poly(DL-lactide)-co-poly(ethylene glycol) (Zhang et al.,
1997), and cellulose esters (Pizzoli et al., 1994). Addition of these polymers,
depending on proportion, results in good miscibility with PHB. Mousavioun et
al. (2010) have studied the thermal properties and miscibility of PHB and lignin
blends and found that PHB/lignin blends are thermally more stable than PHB
over a wider temperature range. Infrared data showed that the miscibility of
blends containing up to 40 wt% lignin was associated with specific hydrogen
bonding interactions between the reactive functional groups in lignin with the
carbonyl groups of PHB (Mousavioun et al., 2010).
Understanding the mechanical and rheological properties of polymer blends is
necessary in establishing changes in the viscoelastic response and processability
conditions. The compatibility of a dispersed component (i.e. filler) within the
matrix can produce highly non-Newtonian response, such as in a monodispersed
crosslinked polymeric spheres of polystyrene in polymethyl methacrylate (Sun et
al., 1993). Aranguren et al. (1992) found that for polymethylsiloxanes mixed
with silica particles, the dynamic moduli showed a strong strain dependence,
while the frequency dependence was dramatically affected with the
concentration of the silica particles. A similar study but on polystyrene
composites containing monodisperse crosslinked polystyrene beads conducted
by Gandhi et al. (1990) showed a uniform decrease in rheological properties due
to increasing bead concentration or a reduction in the crosslink density of the
beads.
The aim of this work is to determine the thermophysical properties and rheology
of PHB/lignin blends and to determine the role lignin plays in PHB viscosity.
The properties of the blends were examined by thermogravimetric analysis
(TGA), differential scanning calorimetry (DSC) and rheological analysis.
4.2. Mater ia ls and Methods
4.2.1. PHB
Bacterial PHB is obtained from Sigma Aldrich. The weight average molecular
weight, Mw as determined by gel permeation chromatography is 440,000 g mol-1
90
while the number average molecular weight, Mn is 260,000 g mol-1. The Tg of
the PHB is 4°C and the melting point is 173°C.
4.2.2. Lignin extraction
Bagasse was obtained from a Mackay Sugar Mill, Queensland, Australia. It was
wet depithed (through a 4.2 mm screen) and then air dried. Lignin was extracted
from bagasse by the soda process using 0.7 M sodium hydroxide solution. The
procedure for lignin extraction and purification has been described elsewhere
(Mousavioun et al., 2010).
4.2.3. Lignin characterisation
Lignin composition was determined by the methods described in the paper by
Mousavioun and co-workers (2010). The results of lignin composition are
presented in Table 4-1.
Tab le 4 - 1 Molecu la r we ig h t o f l i gn in and l ign in co mponent s (wt %) (Mousa v ioun e t a l . , 2010)
Ash* Glucan* Xylan* Arabinan* Purity
2.0 0.2 1.6 <0.1 96.1
* Error in analysis (% ±2)
** Error in analysis (% ±5)
4.2.4. Blend preparation
Lignin and PHB were dried at 100°C and 40°C respectively for 12 h and stored
in desiccators under vacuum prior to use. PHB/lignin blends with lignin contents
from 10 wt% to 90 wt% were mixed in a Haake mini lab twin screw using the
procedure reported by Ghaffar (2002). To minimise PHB degradation, the
Mn
(g mol-1)
Mw
(g mol-1)
Methoxy**
Phenolic
OH**
RCOOH** Total
OH**
2160 2410 10.9 5.1 13.6 14.5
91
temperature of the extruder was maintained at 175°C for 2 min. The polymer
blends were extruded as strands then cooled and pelletised. The pellets were
stored in a desiccator to avoid moisture absorption. Similar processing
conditions were carried out for pure PHB.
4.2.5. Characterisation of blend samples
4.2.5.1. Thermogravimetric analysis (TGA)
The thermal decomposition studies were carried out in a TA Instruments Q500.
Approximately 10 mg of the sample was weighed in an aluminium pan and
analysed by TGA in non-isothermal and isothermal modes.
In the non-isothermal mode, heating was at a rate of 10°C min-1 and was
performed from ambient to approximately 800°C. The test was performed in an
atmosphere of nitrogen, which was injected at a flow rate of 15 mL min-1. A
curve of weight loss against temperature was constructed from the data obtained
by the instrument.
The isothermal runs were performed at 170°C, 180°C and 190°C. To reach the
desired temperature, samples were pre-heated from ambient temperature to that
temperature at a rate of 10°C min-1, and then degraded isothermally for at least
50 min. The test was performed in an atmosphere of nitrogen, which was
injected at a flow rate of 15 mL min-1. A curve of weight loss against
temperature was constructed from the data obtained by the instrument. The
conversion rate curve was produced to indicate the mass loss conversion (%)
during this time.
4.2.5.2. Differential scanning calorimetry (DSC)
Approximately 10 mg of sample was precisely weighed and then encapsulated in
an aluminium pan. The pan was then placed in a DSC-Q2000 instrument and
heated from 0°C to 180°C at a heating rate of 10°C min-1 (cycle 1). The test was
performed in an atmosphere of nitrogen, which was injected at a flow rate of 15
mL min-1. Samples were then cooled at a rate of 30°C min-1, to -10°C (cycle 2).
Samples were then reheated to 180°C at a rate of 10°C min-1 (cycle 3). The plot
obtained from this second heating run shows the Tg as a step transition. It was
difficult to obtain the Tg using DMTA, because of the brittle nature of the blends,
and so this technique was not used in the research study.
92
In addition to Tg, other thermal parameters of PHB/lignin blends were evaluated.
Melting temperature (Tm), melting enthalpy (∆Hm), bulk crystallinity (Xc), cold
crystal temperature (Tcc) and melting crystallisation point (Tmc) are extracted
from DSC thermographs. The bulk crystallinity of a blend was calculated using
the following equation:
}> 2 ∆~�∆~�a�
}>�~5 (4-1)
where ∆�.e0 and }>�~5 are the melting enthalpy and crystallinity of the pure
PHB used in this study. }> is a ratio of ∆�. of the sample and that of the 100%
crystalline PHB (∆��). ∆�� of PHB is assumed to be 146 J g-1 (Barham et al.,
1984). On this basis, the values of ∆�.e0 and }>�~5 used in this study are 92 J
g-1 and 63 % respectively.
4.2.5.3. Rheological analysis
The time and temperature dependent storage modulus (G′), loss modulus (G″)
and complex viscosity (η*) were determined by a Rheometrics Inc. Advanced
Rheometric Expansion System (ARES) with RSI orchestrator software, and
using parallel plate geometry having a plate diameter of 25 mm and a gap of 0.5-
1.0 mm. Disk-type specimens of pure PHB and its blends with diameter of 25
mm and thickness of 0.5 mm were obtained from compression moulded sheets.
The experiments were performed at 175°C over the frequency range of 1 rad s-1
to 100 rad s-1. To minimise the length of the test period and the probable
degradation of PHB, a multi frequency wave was used.
4.3. Resul ts and D iscuss ion
4.3.1. Degradation of PHB
The general rate equation for a decomposition or degradation process can be
described as:
���� 2 k7T8f7�8 (4-2)
where � is the degree of conversion, k7T8 the rate constant, and f7�8 is the
reaction rate model, a function which depends on the actual reaction mechanism.
In this, work
93
�2 YZ�YYZ�Y[
(4-3)
where W� is the initial weight, W is the weight during the experiment, and W� is
the final weight of the investigation determinate from the TG thermograms.
The rate constant k7T8 can be represented by the Arrhenius equation: as
k7T8 2 Ae7�����8 (4-4)
where E� is the apparent activation energy (kJ mol��8, R is the ideal gas constant
(8.314 J. K��.mol��), A is the pre-exponential factor (s��), and T is absolute
temperature (K).
For an isothermal TGA process, combination of equations (4-2), (4-3) and (4-4)
results in
���� 2 Af7�8e7�
����8 (4-5)
Equations are the fundamental expressions of analytical methods to calculate
kinetic parameters on the basis of TGA data.
A linear differential method of equation 4-5 is
m���� n 2 6 ���� 3 7Af7�88 (4-6)
Then within the linear part of isothermal degradation curves, the plots of ����
vs. �� directly leads to 6 ��
� from the slope from which E� is calculated.
On the basis of the report from Hablot et al. (2008), the degradation temperature
of PHB is close to its melting point. Therefore a series of isothermal gravimetric
analyses was undertaken, in order to find the safe temperature range for
processing PHB with lignin (see Section 4.2.5.1). Figure 4-1 shows the mass
loss ratios at different temperatures. The rate of mass loss shows a sharp
increase from 180°C. On the basis of these results, a working temperature of
175°C was selected for the preparation of PHB/lignin blends (see Section
4.2.5.1).
The degradation rate constants, k, at various temperatures were calculated from
the slope of the linear portion of the curves of Figure 4-1 and the results are
detailed in Table 4-2. The k values increase with an increase in temperature.
94
Figure 4-1 Isothermal degradation of PHB
Tab le 4 - 2 Deg radat ion ra te constan t o f PHB a t va r iou s temp era tu res
Temperature (ºC) Degradation rate constant, k (s-1)
170 1.6×10-6
180 3.3×10-6
190 6.0×10-6
The study by Aoyagi et al. (2002) obtained a k value of 1.84×10-6 at 170°C from
the slope of the inverse number-average degree of polymerisation against
reaction time. The Ea value obtained from the same study was
111 kJ mol-1, while in the present study a value of 112 kJ mol-1 was obtained. As
similar k and E� values were obtained, it is probable that a completely random
chain scission mechanism occurs with PHB during isothermal degradation
(Aoyagi et al., 2002).
4.3.2. Degradation of PHB/lignin blends
The thermal degradation of PHB/lignin blends were evaluated by TGA. Figure
4-2 shows the intergral thermogravimetric curves of PHB, lignin and a 50 wt%
PHB/lignin blend. The curves for the other blends have not been included for
the sake of clarity and have been presented by Mousavioun et al. (2010). The
results of Figure 4-2 show that the addition of lignin reduces the amount of
0
1
2
0 10 20 30 40 50
Mas
s lo
ss r
atio
(%
)
Time (min)
190°C
180°C
170°C
95
material lost over the wide range of temperatures investigated. The lower weight
loss is an indication that the blends are thermally more stable than pure PHB.
Figure 4-2 Integral thermogravimetric curves for PHB, lignin and 50 wt% PHB/lignin
However, if the decomposition temperature at which the material has reached 5
wt% degradation (T0) is examined, the addition of lignin appears to accelerate
the initial degradation process (Figure 4-3). This is due to the lignin component
because its T0 value is ~120°C. Thus the shift in the T0 of the blends to lower
temperatures, through the addition of lignin, provides the opportunity to process
the blends at lower temperatures, possibly limiting PHB degradation via random
chain scission mechanisms (Avella et al., 2000).
0
10
20
30
40
50
60
70
80
90
100
100 200 300 400 500 600 700 800
Mas
s (%
)
Temperature (°C)
TG
PHB
Lignin
50 wt% PHB/lignin
96
Figure 4-3 Threshold degradation temperature of PHB/lignin blends
The same trials were examined to evaluate the degradation constant of
PHB/lignin blends with various ratios and temperatures. For instance, the
degradation rate constant for 50 wt% PHB/lignin blend is shown in Table 4-3.
Tab le 4 - 3 Deg radat ion ra te constan t o f 5 0 wt % PHB/ l ign in b lend s a t va r i ous temp era tu res
Temperature (ºC) Degradation rate constant, k (s-1)
170 3.3×10-4
180 3.9×10-4
190 6.1×10-4
The E� values (error ±10%) of PHB/lignin blends were calculated using equation
4-6 and the results are presented in Figure 4-4. There appears to be a rough trend
of increasing E� with an increase in lignin content. However, it also appears that
over 10 wt% to 60 wt% lignin the E� barely changed. The drop of E� from 112
kJ mol-1 for pure PHB to up to half that value with lignin, in fact suggests that
lignin reduces the thermal stability of PHB and that the reduced weight loss
100
120
140
160
180
200
220
240
0 10 20 30 40 50 60 70 80 90 100
T0
(°C
)
Lignin (wt%)
97
observed in the TGA curves is associated with the slower rate of lignin
degradation in the blend.
Figure 4-4 Activation energy of thermal degradation of PHB/Lignin blends
4.3.3. Thermal properties of PHB/lignin blends
The glass transition temperature (Tg) of a polymer blend gives an indication of
the miscibility and processibility of the material. A single Tg implies complete
compatibility between the components. If blending results in a material having a
lower Tg than the brittle or stiff component, this then means that the blend has
more flexible chains thus lowering stiffness as well as improving processibility.
On the other hand, if the blend has a higher Tg and a higher melt viscosity, there
would be an improvement in processibility with no change in chain stiffness. In
a situation where there are two Tgs, the degree of miscibility is restricted.
However, this does not mean that there are no interactions between the
components.
Figure 4-5 shows two DSC thermograms of PHB/lignin blends which represent
the heat flow at the second heating cycle for (a) 40 wt% lignin, and (b) 80 wt%
lignin respectively. This figure shows that for the blend containing 40 wt%
lignin, lignin not only is miscible in the PHB matrix, but also is is acting as a
0102030405060708090
10 20 30 40 50 60 70 80 90
Ea
(kJ
mol
-1)
Lignin%
98
plasticiser by enhancing the Tg of PHB. This will result in some improvement in
the processibility of PHB.
Figure 4-5 DSC thermograms of PHB/lignin blends with (a) 40 wt% lignin, and (b) 80 wt% lignin
The summary of thermal parameters of PHB/lignin blends are shown in Table 4-4.
The Tg of PHB, as well as its melting temperature (Tm), ∆Hm, Xc and Tmc,
decreases with an increase in lignin content, irrespective of the lignin loading. In
general, when the lignin content ≤ 40 wt%, it raises the Tmc (i.e. the melt cold
crystallisation temperature) of the PHB. However, when the lignin content is
≥50wt%, it reduces the Tmc of PHB. Weihua et al. (2004) obtained similar
results at lower lignin contents.
99
Tab le 4 - 4 The rma l p rop e rt i es o f l i gn in / PHB b lends us ing the s ta rt in g l ign in mate r ia l
Sample Tg (°C)* Tm(°C) ∆Hm (J g-1) Xc (%)** Tmc(°C)
PHB 3 172 92 63 89
Lignin content
10 wt%
7
174
90
61
132
20 wt% 9 173 85 58 121
40 wt% 15 170 78 53 98
50 wt% 18 (130) 167 34 23 82
60 wt% 17 (148) 165 31 21 86
70 wt% 21 (134) 157 9
80 wt% 26 (125) 152 5
90 wt% 43 (131) 158 3
Lignin (130)
* Tg with parentheses is lignin, and the one without is PHB
** Xc is for the bulk crystallisation as opposed to the crystallinity of PHB itsels. (see Table 5-2)
4.3.4. Rheological properties of PHB/lignin blends
Melt rheology of composite blends is essential to understand the molten
structural property relationship and their processibility. Preliminary strain sweep
experiments were carried out to determine the extent of the linear viscoelastic
domain. As an example, Figure 4-6 shows complex viscosity (η*) vs strain for
PHB/10 wt% lignin. In all cases the results show that all samples were stable
and showed a linear viscoelastic response at strains ≤ 10%.
100
Figure 4-6 Complex viscosity (η*) versus % strain for PHB/10 wt% lignin Storage modulus ( G′) and loss modulus (G″) of PHB and blends are presented in
Figures 4-7 and 4-8 respectively. The results show that G′ and G″ generally
increase with increase in frequency.
Figure 4-7 Dynamic storage modulus of PHB and PHB/lignin blends
1
10
100
1000
1 10 100
η*
(Pa
s)
Strain (%)
1
10
100
1000
10000
100000
1 10 100
G' (
Pa)
Frequency (rads-1)
Pure PHB 10% Lignin 30% Lignin 60% Lignin 90% Lignin
101
Figure 4-8 Dynamic loss modulus of PHB and PHB/lignin blends Initially as lignin is added to pure PHB, the G′ values at all frequencies (except at
100 rad s-1) are reduced, for the 10 wt% and 30 wt%. At higher lignin contents,
i.e. at 60 and 90 wt%, the G′ values are higher than that of pure PHB for the
entire frequency range. Similar results are seen for G″.
Figure 4-7 shows a slight drop in the G′ of pure PHB at high frequencies (e.g. at
100 rad s-1), which is absent in the PHB/lignin blends. This result probably
implies that the addition of lignin improves the mechanical property of PHB.
The ratio of G″ to G′ is termed tanδ and is the ratio of energy dissipated to
energy stored in one cycle of deformation. Tan δ is small for elastic solids and
large for viscous fluids. Tan δ plots at various frequencies for pure PHB and the
blends are shown in Figure 4-9.
1
10
100
1000
10000
100000
1000000
1 10 100
G"
(Pa)
Frequency (rad/s)
Pure PHB 10% Lignin 30% Lignin 60% Lignin 90% Lignin
102
Figure 4-9 Tan δ of PHB and PHB/lignin blends
Figure 4-9 shows that for pure PHB materials the tan δ ranges from 4 at low
frequencies (somewhat elastic) to 2 (reduction in elasticisty and increase in
viscous nature) at higher frequencies, as expected for many polymer melts
(Ferry, 1980). With the addition of 10 wt% lignin the tan δ increases markedly
(from 10 at low frequencies to 30 at higher frequencies) which implies that they
behave more like a viscous fluid (less elastically) than pure PHB. Thus the
addition of 10 wt% lignin (and to a lesser extent 30 wt% lignin) to PHB, appears
to significantly decreases the elasticity of PHB. However, for the blends
containing 60 wt% lignin, the tan delta is reduced again (below that of pure
PHB) indicating an increased elastic response. It is possible the lignin is
interacting with the PHB to form an elastic lignin-PHB network, and reduces the
ability of the system to dissipate energy in a viscous manner.
Figure 4-10 depicts the complex viscosity (η*) of pure PHB and PHB/lignin
blends.
1
10
100
1 10 100
Tan δ
Frequency (rad s-1)
Pure PHB 10% Lignin 30% Lignin
60% Lignin 90% Lignin
103
Figure 4-10 Complex viscosity (η*) of blends of pure PHB and PHB/lignin
blends
The complex viscosity (η*) of pure PHB shows a typical shear thinning profile
with increasing frequency. Upon addition of 10 wt% lignin the complex
viscosity reduces appreciably across the frequency range, showing that lignin is
increasing the ease of processibilty. (This is in-line with the reduction in
elasticity and increase in viscous nature as seen in Figure 4-9). Further addition
of lignin to 30% increases the viscosity, but it is still lower than pure PHB for
most of the frequency range. Further addition of lignin then increases the
viscosity further and it becomes greater than the pure PHB for most of the
frequency range. Summarising the results reflected in Figures 4-7, 4-8, 4-9 and
4-10, it could be postulated that addition of lignin up to 10 wt% increases the
viscous dissipation of the system, reduces the viscosity (improves processibility),
and the blend act like a single phase plasticised sample (where the plasticiser
reduces the viscosity of the system). Upon further addition of lignin over 10wt%
acompeting additional effect occurs, which sees the elasticity of the system
increase and the viscosity increase. Here it can be postulated that the lignin is
interacting with the PHB matrix like a filler or a second phase that interferes
1
10
100
1000
10000
1 10 100
η*
(Pa
s)
Frequency (rad s-1)
Pure PHB 10% Lignin 30% Lignin
60% Lignin 90% Lignin
104
with the relaxation processes of the PHB matrix. These postulations are in very
good agreement with the Tg data (table 4), which shows that critical changes
from single phase to dual phase behaviour occur at concentrations greater than
40wt% lignin.
4.4. Conclus ion Lignin was found to affect the thermal stability and crystallisation of PHB. The
TGA and DSC of the PHB/lignin blends suggest that intermolecular interactions
between PHB and lignin were favoured at a lignin content of up to 40 wt%.
Rheological study shows lignin content of 10 wt% and 30 wt% plasticises PHB
and results in the formation of a single phase, while 60 wt% and 90 wt% lignin
present a two phase PHB/lignin blend systems.
105
4.5. References An, Y., Dong, L., Xing, P., Zhuang, Y., Mo, Z., Feng, Z., 1997. Crystallization
kinetics and morphology of poly(β-hydroxybutyrate) and poly(vinyl acetate) blends. Eur. Polym. J. 33, 1449-1452.
Antunes, M.C.M., Felisberti, M.I., 2005. Blends of poly(hydroxybutyrate) and poly(ε-caprolactone) obtained from melting mixture. Polym. Sci. Technol. 15, 134-138.
Aoyagi, Y., Yamashita, K., Doi, Y., 2002. Thermal degradation of poly[(R)-3-hydroxybutyrate], poly[ε-caprolactone], and poly[(S)-lactide]. Polym. Degrad. Stab. 76, 53-59.
Aranguren, M.I., Mora, E., DeGroot, J.V., Macosko, C.W., 1992. Effect of reinforcing fillers on the rheology of polymer melts. J. Rheol. 36, 1165.
Avella, M., Rota, G.L., Martuscelli, E., Raimo, M., Sadocco, P., Elegir, G., Riva, R., 2000. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and wheat straw fibre composites: thermal, mechanical properties and biodegradation behaviour. J. Mater. Sci. 35, 829-836.
Barham, P.J., Keller, A., Otun, E.L., Holmes, P.A., 1984. Crystallization and morphology of a bacterial thermoplastic: poly-3-hydroxybutyrate J. Mater. Sci. - Mater. Med. 19(9), 2781-2794.
Chiu, H.J., Chen, H.L., Lin, J.S., 2001. Crystallization induced microstructure of crystalline/crystalline poly(vinylidenefluoride)/poly(3-hydroxybutyrate) blends probed by small angle X-ray scattering. Polymer 42, 5749-5754.
Ferry, J.D., 1980. Viscoelastic properties of polymers, 3rd ed. John Wiley, New York.
Gandhi, K., Park, M., Sun, L., Zou, D., Li, C.X., Li, Y.D., Aklonis, J.J., Salovey, R., 1990. Model-filled polymers. II. Stability of polystyrene beads in a polystyrene matrix. J. Polym. Sci. Pol. Phys. 28, 2707-2714.
Ghaffar, A.M.E.A., 2002, Development of a biodegradable material based on Poly(3-hydroxybutyrate) PHB, In, Martin-Luther University, Wittenberg, pp. 115.
Hablot, E., Bordes, P., Pollet, E., Avérous, L., 2008. Thermal and thermo-mechanical degradation of poly(3-hydroxybutyrate)-based multiphase systems. Polym. Degrad. Stab. 93, 413-421.
Mousavioun, P., Doherty, W.O.S., George, G., 2010. Thermal stability and miscibility of poly(hydroxybutyrate) and soda lignin blends. Ind. Crops Prod. 32, 656-661.
Pizzoli, M., Scandola, M., Ceccorulli, G., 1994. Crystallization kinetics and morphology of poly(3-hydroxybutyrate)/cellulose ester blends. Macromolecules 27, 4755-4761.
Sun, L., Aklonis, J.J., Salovey, R., 1993. Model filled polymers. XIV: Effect of modifications of filler composition on rheology. Polym. Eng. Sci. 33, 1308-1319.
Weihua, K., He, Y., Asakawa, N., Inoue, Y., 2004. Effect of lignin particles as a nucleating agent on crystallization of poly(3-hydroxybutyrate). J. Appl. Polym. Sci. 94, 2466-2474.
Xing, P., Dong, L., An, Y., Feng, Z., Avella, M., Martuscelli, E., 1997. Miscibility and crystallization of poly(β-hydroxybutyrate) and poly(p-vinylphenol) blends. Macromolecules 30, 2726-2733.
106
Yoshie, N., Azuma, Y., Sakurai, M., Inoue, Y., 1995. Crystallization and compatibility of poly(vinyl alcohol)/poly(3-hydroxybutyrate) blends: influence of blend composition and tacticity of poly(vinyl alcohol). J. Appl. Polym. Sci. 56, 17-24.
Zhang, L., Deng, X., Zhao, S., Huang, Z., 1997. Biodegradable polymer blends of poly(3-hydroxybutyrate) and poly(DL-lactide)-co-polyethylene glycol. J. Appl. Polym. Sci. 65, 1849-1856.
107
CHAPTER 5
Environmental degradation of soda
l ignin/ poly(hydroxybutyrate) blends
Payam Mousaviouna, Graeme A. Georgeb and William O.S. Dohertya
a Sugar Research and Innovation, Centre for Tropical Crops and Biocommodities, Queensland University of Technology, GPO Box 2434, Brisbane, Australia. b Chemistry Discipline, Faculty of Science and Technology, Queensland University of Technology, GPO Box 2434, Brisbane, Australia. Submitted to the Journal of Polymer Degradation and Stability, 2011
Research Students Centre, Level 4, 88 Musk Avenue, Kelvin Grove Campus, GPO Box 2434. Brisbane QLD 4001
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Correct as at: 7-6-10
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In the case of this chapter: Publication title and date of publication or status: Thermal Decomposition of Bagasse: Effect of Different Sugar Cane Cultivars, published in Industrial & Engineering Chemistry Research, Vol 50, 791-798, 2011
Contributor Statement of contribution* Payam
Mousavioun
Data analysis. Signature
Date Vanita R. Maliger
Experimental design and conducted experiments.
William O. S. Doherty Wrote the manuscript,
Data analysis.
Ray L. Frost Edited manuscript.
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108
Abstract- Blends of lignin and poly(hydroxybutyrate) (PHB) were obtained
using melt extrusion. Film samples were prepared by compression-moulding and
environmental degradation assessed by a burial test in soil for up to 12 months.
The extent and mechanism of degradation of lignin/PHB blends were
investigated by gravimetric analysis, thermogravimetric analysis (TGA),
differential scanning calorimetry (DSC), X-ray Photoelectron Spectroscopy
(XPS), scanning electron microscopy (SEM) and Fourier transform infrared
spectroscopy (FT-IR) over the entire range of compositions. Based on
gravimetric analysis, PHB films disintegrated and lost 45 wt% of initial mass in
soil within 12 months. In contrast, inhibition of PHB degradation by even low
concentrations of lignin was observed. It also showed lignin slowed down the
rate of degradation of blends. TGA showed the degradation profile of PHB and
miscible ratios of lignin and PHB (in lignin content of less than 40 wt%) do not
change with time. However, due to immiscible ratio profiles, the rate of
degradation is more rapid at longer buried time. According to the DSC results,
lignin increased the crystallinity of PHB in miscible portions and decreased the
crystallinity of PHB in the immiscible region. Also, DSC results exhibited
hydrogen bonding of lignin with PHB plays a significant role to protect PHB
against degradation. XPS data revealed an accumulation of biofilms on surface
of buried film samples. FT-IR displays disintegration in PHB, along with an
increase in lignin intensity in blends. SEM monitors surface roughness of buried
samples.
5.1. I ntroduct ion Producing biodegradable plastics and materials has been suggested in response
to increased awareness of the environmental hazards with disused plastics
(Sticklen, 2008). One such material is poly(hydroxybutyrate) (PHB) which is
totally biodegradable and can be produced by fermentation of sugars and other
chemicals or in plants (Sticklen, 2008). PHB has attracted much commercial
interest as a plastic material because its physical properties are remarkably
similar to those of polypropylene (PP), even though the two polymers have quite
different chemical structures. PHB exhibits a high degree of crystallinity, has a
high melting point of approximately 173°C, and most importantly, unlike PP,
109
PHB is rapidly biodegradable (Grassie, et al., 1984). PHB consumption, at
present, is mostly restricted in medical application because of its high cost
compared to synthetic plastics (Grassie, et al., 1984). Two major factors which
currently inhibit the widespread use of PHB are its high cost and poor
mechanical properties. The production costs of PHB are significantly higher
than for plastics produced from petrochemicals, and its stiff and brittle nature
makes processing difficult and impedes its ability to handle high impact. Several
attempts have been made to improve the physical properties of PHB by blending
it with other biodegradable polymers found to be miscible with PHB, such as
poly(ξ-caprolactone) (Antunes and Felisberti, 2005), poly(vinylidene fluoride)
(Chiu, et al., 2001), poly(vinyl alcohol) (Yoshie, et al., 1995), poly(lactic acid)
(Zhang, et al., 1996), poly(vinyl acetate) (An, et al., 1997), poly(vinyl phenol)
(Xing, et al., 1997), poly(DL-lactide)-co-poly(ethylene glycol) (Zhang, et al.,
1997), and cellulose esters (Pizzoli, et al., 1994).
Biodegradation of polymer blends is determined by both degradability of blend
components themselves and the blend composition. Woolnough et al. (2010)
studied the biodegradation of PHB and some other “green plastics” in mature
soil by detecting mass loss, topographical changes and biofilm attachment and
found that PHB itself has a better degradability than polyhydroxyoctanoate,
poly-DL-lactide and ethyl cellulose. In a composite, the component with the
lower degradation rate, might inhibit the degradation of the composite. Kumagai
and Doi (1992) found the degradation of PHB in the blend is restricted by
Polyvinyl acetate (PVAc). PVAc which is non-degradable remains on the surface
of buried PHB/PVAc blends and protects the blend against biodegradation. Also,
Wu (2006) found the mechanical properties of PHB/wood flours became
significantly worse compared with PHB, due to poor compatibility between
those two.
Understanding the biodegradation properties of blends is essential to establish
the biodegradability of blends and tailor the composition of blends to increase
sustainability. Avella et al. (2000) showed that the reinforcement of PHB with
wheat straw does not affect its biodegradation in long term soil burial tests.
Ikejima et al. (1998) found that the degradation profiles of the PHB/Polyvinyl
alcohol (PVA) blend films depended on their blend composition. The blend films
110
with PHB-rich composition showed a higher degradation rate and higher final
degraded ratio than the pure PHB film. Lim et al. (2005) studied the effect of
acidity of soil on degradation of medium-chain-length polyhydroxyalkanoates
(PLA) and found that acidic soils accelerate the degradation of PLA. Scott
(2002) has referred to the fact that lignocellulose, due to its hydrophobicity and
chemical inertness, does not readily degrade either abiotically or biotically and
when it does biodegrade, the lignin tends to accumulate. Lignin biodegrades
slowly to an extent of 17-53 wt% in every 100 days. So, PHB is expected to be
the main target for biodegradation in this study.
The aim of this work is to determine the environmental degradation properties of
PHB/lignin blends and to determine the role lignin plays in either accelerating or
retarding PHB degradation. The structure and environmental properties of the
blends were examined by gravimetric, thermogravimetric analysis (TGA),
differential scanning calorimetry (DSC), scanning electron microscopy (SEM),
X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared
spectroscopy (FT-IR) over a wide range of compositions.
5.2. Mater ia ls and Methods
5.2.1. PHB
Bacterial PHB was obtained from Sigma Aldrich. The weight average molecular
weight, Mw as determined by gel permeation chromatography is 440,000 g mol-1
while the number average molecular weight, Mn is 260,000 g mol-1. The Tg of
the PHB is 4°C and the melting point is 173°C.
5.2.2. Lignin
Lignin was extracted from bagasse obtained from the Mackay Sugar Mill,
Queensland, Australia. It was wet depithed in particles less than 4.2 mm and
washed and then air dried. Lignin was extracted from bagasse by the soda
process using 0.7 M sodium hydroxide solution. The procedure for lignin
extraction and purification has been described elsewhere (Mousavioun, et al.,
2010).
111
5.2.3. Lignin characterisation
Lignin composition was determined by the methods described in the paper by
Mousavioun and co-workers (2010). The results of lignin composition are
presented in Table 5-1.
Tab le 5 - 1 Molecu la r we ig h t o f l i gn in and l ign in co mponent s (wt %) (Mousa v ioun e t a l . , 2010)
Ash* Glucan* Xylan* Arabinan* Purity
2.0 0.2 1.6 <0.1 96.1
Mn (g mol-1)
Mw
(g mol-1) Methoxy** Phenolic
OH** RCOOH** Total OH**
2160 2410 10.9 5.1 13.6 14.5
*Error in analysis (% ±2) ** Error in analysis (% ±5)
5.2.4. Blend preparation
Lignin and PHB were dried at 100°C and 40°C respectively for 12 h and stored
in desiccators under vacuum prior to use. PHB/lignin blends with lignin contents
from 10 wt% to 90 wt% were mixed in a Haake mini lab twin screw using the
procedure reported by Ghaffar(2002). To minimise PHB degradation, the
temperature of the extruder was maintained at 175°C for 2 min. The polymer
blends were extruded as strands then cooled and pelletised. The pellets were
stored in a desiccator to avoid moisture absorption. Similar processing
conditions were carried out for pure PHB. The previous work on PHB/lignin
blends showed that lignin, up to 30 wt% content, is miscible in a PHB matrix
(Mousavioun, et al., 2010).
5.2.5. Polymer film fabrication
Polymer films were prepared using a hot press instrument under 7.5 bar pressure
and 175°C. To produce film samples with the same thickness a rectangular
mould with the thickness of 100µm was used. Film samples were prepared by
compression moulding between two Teflon sheets. All film samples moulded in
rectangular shape with the dimension of 45mm x 30mm and thickness of 100µm.
112
Films were subsequently removed and further dried under vacuum (48h, 25°C)
before standing for a further 24h (25°C, relative humidity 30%) until their
weights had atmospherically equilibrated (0.18-0.52g). The films were then
aged for three weeks to enable their crystallinity to reach an equilibrium value
and then films were carefully inserted in slide frames.
5.2.6. In situ biodegradation of polymer films in soil
In situ environmental degradation was conducted on site in garden soil (Pinjarra
Hills Field Station, University of Queensland, Australia). The procedure
followed was similar to that reported by Woolnough. (2010) All soil was sieved
to particles of less than 2mm in diameter and mixed completely before burial of
polymer samples. The samples were buried as per ASTM D 5988 in three
1.0x0.7 m2 plots (samples buried for 4, 8 and 12 months individually). The soil
of each plot had a pH of 6.7 as measured according to ASTM D 4972, a
temperature of 12-27°C and water content that varied with rain patterns at ~20%.
Polymer films were buried at least 2 cm apart and 20 cm below the soil surface.
The special arrangement of the burial ensured that the total polymer weight did
not exceed 7.7 wt% of soil (ASTM D 6003). Every 2 months soil from one of
the three plots was removed and the temperature, pH and water content were
measured. The experiment continued for 52 weeks. Soil was removed from the
polymer film by immersing in a solution containing 0.25 wt% sodium
hypochlorate, prior to drying under vacuum (84 hr, 25°C) and then weighed. The
soil removal protocol and preparation of films again followed the method
suggested by Woolnough (2010).
5.2.7. Thermogravimetric analysis (TGA)
The thermal decomposition studies were carried out in a TA Instruments Q500
thermogravimetric analyser. Approximately 10 mg of sample was weighed into
an aluminium pan and analysed by TGA by non-isothermal and isothermal
methods.
In the non-isothermal mode, heating was at a rate of 10°C min-1 and was
performed from ambient to approximately 800°C. The test was performed in an
113
atmosphere of nitrogen, which was injected at a flow rate of 15 mL min-1. A
curve of weight loss against temperature was constructed from the data obtained
by the instrument.
The isothermal runs were performed at 170°C, 180°C and 190°C. To reach the
desired temperature, samples were pre-heated from ambient to the set
temperature at a rate of 10°C min-1, and then degraded isothermally for at least
50 min. The test was performed in an atmosphere of nitrogen, which was
injected at a flow rate of 15mL min-1. A curve of weight loss against
temperature was constructed from the data obtained by the instrument. The
conversion rate curve was produced to indicate the mass loss conversion (wt%)
during the time.
5.2.8. Differential scanning calorimetry (DSC)
Approximately 5 mg of sample was precisely weighed and then sealed in an
aluminium pan. The pan was then placed in a DSC-Q2000 instrument and
heated from 0°C to 175°C at a heating rate of 10°C min-1 (cycle 1). The test was
performed in an atmosphere of nitrogen, which was injected at a flow rate of 15
mL min-1. Samples were then cooled at a rate of 30°C min-1, to -10°C (cycle 2).
Samples were then reheated to 180°C at a rate of 10°C min-1 (cycle 3). The plot
obtained from this second heating run shows the Tg as a step transition.
In addition to Tg, other thermal parameters of PHB/lignin blends were evaluated.
Melting temperature (Tm), melting enthalpy (∆Hm), PHB crystallinity (X)!), and
melt cold crystallinity temperature (Tmc) were extracted from DSC
thermographs. The crystallinity of PHB (not that of the blends) was calculated
using the following equation:
X)! 2 ∆&�∆&���
���������
(5-1)
where ∆H��� is melting enthalpy and X!%&' and x%&' are crystallinity and mass
ratio of PHB used in this study. X!%&' is a ratio of ∆Hm of the sample PHB and
that of 100% crystalline PHB (∆H0). ∆H0 of PHB is assumed to be 146 J g-1
(Barham, et al., 1984). On this basis, the values of ∆H��� and X!%&' used in this
study are 92 J g-1 and 63 % respectively.
114
To evaluate the interaction between PHB and lignin, a well-known equation
suggested by Kwei is employed.
Kwei equation: 9t7qi_@r8 27sLOp,L���sMOp,M8
7sL���sM83 yu�uR (5-2)
where Tz,� {| R and w� {| R are glass transition temperatures of the pure
components and their corresponding weight fractions, respectively. K� and q are
adjustable parameters. A relatively higher q indicates a stronger hydrogen
bonding between those two components (ElMiloudi, et al., 2009).
5.2.9. X-ray photoelectron spectroscopy analysis
XPS data were acquired using a Kratos Axis ULTRA X-ray photoelectron
spectrometer, incorporating a 165 mm hemispherical electron energy analyser.
The incident radiation was monochromatic Al Kα X-rays (1486.6 eV) at 150 W
(15 kV, 10 mA) and at 45 degrees to the sample surface. Photoelectron data
were collected at take off angle of 90°. Survey (wide) scans were taken at an
analyser pass energy of 160 eV and multiplex (narrow) high resolution scans,
which focus on a particular atom, at 20 eV. Survey scans were carried out over
1200 eV - 0 eV BE range with 1.0 eV steps and a dwell time of 100 ms. Narrow
high-resolution scans were run with 0.05 eV steps and 250 ms dwell time. Base
pressure in the analysis chamber was 1.0 x 10-9 torr and during sample analysis
1.0 x 10-8 torr. Atomic concentrations were calculated using the Kratos Vision 2
software and a linear baseline.
5.2.10. Scanning electron microscopy (SEM)
The morphology of the lignin/PHB blends was examined using a scanning
electron microscope, FEI Quanta 200 Environmental SEM, at an accelerating
voltage of 15 kV. For this examination the pellets were compression moulded
between two sheets of Teflon using an established procedure (Ghosh, et al.,
1999). To obtain better images of film topography, micrographs were taken at a
tilt of 35˚.
115
5.2.11. Fourier transform-infrared spectroscopy (FT-IR)
IR spectra were collected using a Nicolet 870 Nexus Fourier transform infrared
(FT-IR) spectrometer equipped with a Smart Endurance single bounce diamond
ATR accessory (Nicolet Instrument Corp., Madison, WI). Spectra were
manipulated and plotted with the use of the GRAMS/32 software package
(Galactic Corp., Salem, NH). Spectra were collected in the spectral range 4000
to 525 cm-1, using 64 scans at 4 cm-1 resolution with a mirror velocity of 0.6329
cm s-1. The measurement time for each spectrum was around 60 s.
5.3. Resul ts and D iscuss ion
5.3.1. Gravimetric analysis
To investigate how the mass of buried samples changed with time, there are two
approaches which are shown below.
Figure 5-1 shows how a wide range of polymer films which were blended from
PHB and 10 wt% to 90 wt% lignin compare with PHB with respect to mass
reduction in incremental periods of 4 months burial during a year.
Figure 5-1 clearly shows a significant difference between the degradation rates
of pure PHB compared to those blends with lignin. The obvious effect of even
small concentrations of lignin to retard degradation of PHB is shown in a
different plot of the gravimetric data in Figure 5-2. Figure 5-2 depicts the trends
of actual mass loss of different lignin/PHB blends, after 4 months, compared
with the expected mass loss of those blends in which PHB is assumed to act as
the only degradable component in blend (ie. a rule of mixtures plot). Figure 5-2
shows that once lignin is added to form a PHB blend the degradation is inhibited.
This could arise either by a biochemical protection effect of lignin against attack
by bio organisms on PHB (Dizhbite et al., 2004) or surface segregation of lignin
from the blend inhibiting biofilm formation and access to the PHB (Cronin,
2008) . The possible surface segregation of lignin has been probed by XPS, as
discussed later.
116
Figure 5-1 Buried mass loss of pure and blended PHB with lignin
(Error in analysis % ±5)
Figure 5-2 Actual and expected mass ratio of lignin/PHB blends after 4
months soil burial. (Error in analysis % ±5)
0.5
0.6
0.7
0.8
0.9
1
0 4 8 12
Mas
s ra
tio
Months
Pure PHB 10% Lignin 40% Lignin60% Lignin 90% Lignin
0.6
0.7
0.8
0.9
1
0 10 20 30 40 50 60 70 80 90
Mas
s ra
tio
Lignin %
Actual mass ratio Expected mass ratio
117
5.3.2. Thermogravimetric analysis
The mass ratio of pure PHB, pure lignin and a blend of PHB with 60 wt% lignin
(after burial) during thermal degradation up to 500°C are given in Figure 5-3.
Figure 5-3 Mass ratio on thermal degradation of PHB, lignin, 30 and 60 wt% lignin blends after 4, 8 and 12 months of burial test
PHB is prone to thermal degradation and decomposes by a three-step
mechanism. Firstly, in the temperature range of 170°C to 200°C, volatile
monomeric, dimeric, trimeric and tetrameric species are formed. This
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
200 250 300 350 400 450 500
Mas
s ra
tio
Temperature (°C)
Pure PHB-4m Pure PHB-8m Pure PHB-12m
30% lignin-4m 30% lignin-8m 30% lignin-12m
60% lignin-4m 60% lignin-8m 60% lignin-12m
lignin
lignin
60% lignin
12m 8m 4m
30% lignin4,8,12m
PHB4,8,12m
118
mechanism of random chain scission (Figure 5-4) has been demonstrated by
mass spectroscopy/FT-IR (Grassie, et al., 1984, Hablot, et al., 2008).
Figure 5-4 PHB random chain scission at temperatures of 170ºC-200ºC
When the temperature is increased from 200ºC to 300ºC, the second step of the
degradation occurs. Within this temperature range, PHB oligomers are broken
down to a free monomeric unit of crotonic acid, pictured in Figure 5-5.
Figure 5-5 PHB chain scission at temperature of 200ºC- 300ºC
Based on the third step of the PHB degradation mechanism, when the
temperature reaches 500ºC, the only species observed are carbon dioxide and
propane. PHB appears to have two main overall degradation steps, while lignin/
PHB degradation occurs in several more stages (Mousavioun et al., 2010) as is
shown in Figure 5-3. Figure 5-3 generally shows that addition of lignin increases
the degradation temperature of PHB. Figure 5-3 shows that for PHB and
miscible blends, the thermal degradation profile was independent of burial time.
However, for the immiscible blends (e.g., 60 wt% lignin), longer burial times
increased the rate of degradation.
119
5.3.3. Differential scanning calorimetry (DSC)
Changes in transition temperatures by DSC analysis, give insight into chemo-
physical and structural changes due to biodegradation of lignin/PHB blends.
Thus, in addition to the use of Tg, other thermal parameters of PHB/lignin blends
like melting temperature (Tm), apparent melting enthalpy (∆Hm) and melt cold
crystallinity temperature (Tmc) of blends with different ratios, , permit us to
obtain a relative crystallinity scale (X!) which is useful to compare the samples.
DSC data of the lignin/PHB blends, compared with pure PHB after burial of 4, 8
and 12 months, are summarised in Table 5-2. This table clearly shows that the
degree of crystallinity of PHB is changed by lignin content. In lower lignin
contents (miscible ratios of lignin/PHB blends) addition of lignin, increases the
crystallinity of PHB. To the contrary, higher lignin contents (immiscible ratios
of lignin/PHB blends) has no affect on crystallinity of PHB (Weihua et al. (2004)
obtained similar result at lower lignin content). Accordingly, the chain scissions
that occur in PHB blocks are probably responsible for the decrease in Tm. The
reason for decrease in ∆Hm of PHB phase may be due to irregularity of the chain
formed, due to branching and cross-linking. In general, when the lignin content
is less than 50 wt%, it enhances the crystallisation of PHB. However, when the
lignin is more than 50 wt%, it retards the crystallisation of PHB.
120
Tab le 5 - 2 The rma l p rop e rt i es o f v i rg in l i gn in / PHB b lends ca st f i lms a t d i f fe ren t ra t i os a nd b iodeg raded
a f te r 4 , 8 and 12 month s
Sample Tg (°C)* Tm(°C) ∆Hm (J g-1) })>7%8 * * Tmc(°C)
PHB 3 172 92 63 89
Virg
in li
gnin
/PH
B b
lend
10/90 7 174 90 68.8 132
20/80 9 173 85 72.5 121
40/60 15 170 78 88 98
50/50 18 (130) 167 34 46 82
60/40 17 (148) 165 31 52.5 86
70/30 21 (134) 157 9 N.A. N.A.
80/20 26 (125) 152 5 N.A. N.A.
90/10 43 (131) 158 3 N.A. N.A.
Lig
nin/
PH
B b
lend
af
ter
4 m
onth
s
10/90 10 169.3 75.7 57.7 115
20/80 12 161 (169) 68.9 48.7 96
30/70 18 164 53.9 52.8 103 40/60 10 163.2 47 53.3 88.5 50/50 N.A. N.A. N.A. N.A. N.A. 60/40 15 (131) 154 19.7 32.5 82 70/30 21 (131) 151 3.8 N.A. N.A. 80/20 24 (131) 151 2.5 N.A. N.A. 90/10 60 (135) N.A. N.A. N.A. N.A.
Lig
nin/
PH
B b
lend
af
ter
8 m
onth
s
10/90 11 168.9 81.7 62.2 120.7 20/80 13 163 53.4 46.2 109 30/70 16 159 (168) 58.7 57.1 104 40/60 16 165 54.3 61.6 91 50/50 N.A. N.A. N.A. N.A. N.A. 60/40 17 (139) 161.6 35.17 60 87 70/30 22 (131) 151 2.87 N.A. N.A. 80/20 25 (135) N.A. N.A. N.A. N.A. 90/10 60 (131) N.A. N.A. N.A. N.A.
Lig
nin/
PH
B b
lend
af
ter
12 m
onth
s
10/90 13 169 84 64.4 119 20/80 14 160 (167) 69 58.7 108 30/70 18 163 (169) 65 63 107 40/60 11 163 46 53 96 50/50 N.A. N.A. N.A. N.A. N.A. 60/40 15 (139) 159 32 55 85 70/30 N.A. N.A. N.A. N.A. N.A. 80/20 25 (146) N.A. N.A. N.A. N.A. 90/10 60 (132) N.A. N.A. N.A. N.A.
* Tg without parentheses is pure PHB and the one with parentheses is lignin
** X’ c is for PHB crystallinity as opposed to the bulk crystallinity of PHB (see Table 4-4)
121
Using the outcomes of Figure 5-1, together with the assumption that almost all of
degradation is due to PHB, the q value which satisfies the evaluated Tgs of 4
months buried blends is equal to 52, where Mousavioun and co-workers (2010)
found that q was equal to 22 for the same blend before the burial test. That
significant increase in q could represents a significant increase in hydrogen
bonding of lignin/PHB blend after 4 months burial. This hypothesis is proposed
that the less strongly bonded PHB is susceptible to degradation and the hydrogen
bonding of lignin with PHB plays a significant role to protect PHB against
degradation.
5.3.4. XPS analysis
Survey analysis of pure PHB and lignin are shown in Figure 5-6. Unexpectedly,
the PHB was found to contain a significant nitrogen signal suggesting
contamination. The nitrogen was found to be present at an atomic concentration
of approximately 3.5 %. The signal observed at a BE of 399.97 eV may indicate
that the nitrogen is present in the form of an amide or a polypeptide fragment of
a protein. As noted in the experimental section, the PHB was of bacterial origin
and the nitrogen contamination is most likely a remnant of the fermentation and
extraction process used to produce the PHB (Hablot, et al., 2008) .
The multiplex carbon 1s scan of pure PHB portrayed in Figure 5-6 (c) is
comparable with the standard PHB which is reported by Beamson and Briggs
(1992) except for the effect of the peptide which results in a broadening of
the C-O band in the spectrum due to an underlying C-N band at 286eV in Figure
6 (c).
122
(a) (b)
(c) (d)
Figure 5-6 Survey XPS of (a) PHB and (b) lignin and multiplex scans of carbon bonds of (c) PHB and (d) lignin
Multiplex XPS scans of carbons for 20 wt% lignin content blends are shown in
Figure 5-7. This figure clearly depicts the differences between zero time and 4
months buried films. There is evidence of surface contamination with the
presence of Si 2p signal. This is indicative of a silica/clay mineral. Total
removal of clay and other surface contamination from buried samples is difficult,
despite the cleaning protocol adopted in these trials. The COO content drops
123
from 12.46 wt% to 3.05 wt% after 4 months burial time. This is suggestive of
PHB degradation. Also, the atomic concentration of oxygen involved in O―C
linkages has reduced from 11 to 6 % further supporting PHB degradation. The
CO content increased from 14.7 to 21 wt%, most likely indicating an increase in
lignin content after 4 months burial time. On the basis of these data, the
hypothesis that lignin in the blend completely covered the surface of the film is
not valid.
As the nitrogen content increased in the sample buried for 4 months (Figures 5-6
and 5-7), it shows biofilm attachement resulting from fermentation.
(a) (b)
Figure 5-7 Multiplex carbon scan of 20 wt% lignin films at (a) zero time and (b) 4 months buried.
5.3.5. FT-IR analysis
Figure 5-8 shows the IR spectrum of PHB, lignin and a 4 months aged 10 wt%
lignin/PHB blend. IR spectra of lignin show a strong hydrogen bonded O―H
stretching absorption around 3400 cm-1 and a prominent C―H stretching
absorption around 2900 cm-1 (Pandey, 1999). PHB spectrum exhibits main two
124
peaks, these are at 1733 cm-1 and 1722 cm-1, though the first peak at 1733 cm-1 is
more of a shoulder to the main peak at 1722 cm-1. The peak at 1733 cm-1 is
associated with the amorphous component of PHB, the peak at ~1722 cm-1 is
associated with the crystalline component of PHB (in its preferred
conformation), and the peak at 1655 cm-1 is associated to ─C═C─ stretching
vibration (Li, et al., 2003). The band at 1685 cm-1 has been reported to be a
crystalline band, although its origin is not known (Guo, et al., 2010). All the
buried blends contain some extra peaks compared with PHB and lignin. These
peaks generally are seen from 3697 cm-1 to 3620 cm-1 which have been reported
as indicative of kaolin (Farmer, 1974) which showed there was some soil
remaining on the films.
Figure 5-8 FT-IR spectra of (a) PHB, (b) lignin and (c) 4 months buried, 10 wt% lignin/PHB blend
125
(a)
(b)
Figure 5-9 FT-IR spectra of the carbonyl stretching region of (a) Pure PHB
and (b) 10 wt% lignin/PHB blend
To examine chemical changes in pure PHB and lignin/PHB blends with different
ratios, the IR spectra of the buried cast films were recorded at various times.
126
Figure 5-9 shows the FT-IR spectra from 1850 cm-1 to 1400 cm-1 of the carbonyl
stretching region of PHB and lignin/PHB blends.
Based on Figure 5-9 for all blend ratios of lignin/PHB, decreases in intensity of
amorphous PHB after 4 and 12 months shows that most of PHB lost was from
the amorphous phase. This result confirms the thermal analysis of buried films
which was explained in section 5.3.3 and XPS results in section 5.3.4.
The band at 1655 cm-1 is associated with ─C═C─ group (Figure 5-9). The
intensity of this peak increased at 4 months and remains at that intensity at 12
months for films containing only PHB. However, the peak intensity increased
with burial time for the blend containing 10 wt% lignin. The increase in the
amount of ─C═C─ group, and hence peak intensity, is associated with PHB
degradation.
Figure 5-9 shows the intensity of the peak at 1685 cm-1 (a crystalline band of
PHB) decreases with burial time. This is an indication of decrystallisation of
PHB with burial time.
5.3.6. Macroscopic and microscopic changes
SEM of the blended films of lignin/PHB films and PHB together with the images
of macro films are shown in Table 5-3. Those micrographs are taken with
magnification of 2000. These images which represent the topography of films
show the roughness of films generally increased during the burial test. Also,
Table 3 shows the roughness of PHB film has increased significantly after 12
months and nearly 30% of its surface degraded completely while, the roughness
of those films which has lignin on it, have not changed. Also, microscopic
images show the films with higher lignin content remained smoother after 12
months burial. So, the lignin plays a significant role to resist against degradation
of films with burial time which confirms the gravimetric and FT-IR results
defined in sections 5.3.1 and 5.3.4.
127
Tab le 5 - 3 Mac ro and M ic ro f i lms o f PHB and l i gn in / PHB b lend s (sca le ba r= 1 5 mm fo r Mac ro and 40
µ m fo r M ic ro f i lms)
Macro film Microfilm Virgin 12 months Virgin 12 months
Pure PHB
30/70 Lignin/PHB
90/10 Lignin/PHB
5.4. Conclus ion PHB is the main component of lignin/PHB blend which is susceptible to
biodegradation. Experimental investigations and analysis of lignin/PHB blends,
clearly depict that the lignin makes a considerable effect on biodegradation
properties of PHB. Lignin inhibited the biodegradation of PHB significantly. In
immiscible ratios of lignin/PHB blends the inhibition on degradation was
observed. This might happen because lignin inhibited PHB random chain
scission rate or it protects PHB against biodegradation attack.
Acknowledgements The authors thank Dr Barry Wood (The University of Queensland) and Dr Llew
Rintoul (Queensland University of Technology) for their cooperation in the XPS
and FT-IR aspects, respectively, of this work.
128
5.5. References An, Y., Dong, L., Xing, P., Zhuang, Y., Mo, Z., Feng, Z., 1997. Crystallization
kinetics and morphology of poly(β-hydroxybutyrate) and poly(vinyl acetate) blends. Eur. Polym. J. 33, 1449-1452.
Antunes, M.C.M., Felisberti, M.I., 2005. Blends of poly(hydroxybutyrate) and poly(ε-caprolactone) obtained from melting mixture. Polym. Sci. Technol. 15, 134-138.
Avella, M., Rota, G.L., Martuscelli, E., Raimo, M., Sadocco, P., Elegir, G., Riva, R., 2000. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and wheat straw fibre composites: thermal, mechanical properties and biodegradation behaviour. J. Mater. Sci. 35, 829-836.
Barham, P.J., Keller, A., Otun, E.L., Holmes, P.A., 1984. Crystallization and morphology of a bacterial thermoplastic: poly-3-hydroxybutyrate J. Mater. Sci. - Mater. Med. 19(9), 2781-2794.
Chiu, H.J., Chen, H.L., Lin, J.S., 2001. Crystallization induced microstructure of crystalline/crystalline poly(vinylidenefluoride)/poly(3-hydroxybutyrate) blends probed by small angle X-ray scattering. Polymer 42, 5749-5754.
Cronin, D.J., 2008, Formation of multi-component films using anionic liquid, Honours Chemistry Thesis In, Queensland University of Technology, Brisbane.
Dizhbite, T., Telysheva, G., Jurkjane, V., Viesturs, U., 2004. Characterization of the radical scavenging activity of lignins--natural antioxidants. Bioresource Technol. 95, 309-317.
ElMiloudi, K., Djadoun, S., Sbirrazzuoli, N., Geribaldi, S., 2009. Miscibility and phase behaviour of binary and ternary homoblends of poly(styrene-co-acrylic acid), poly(styrene-co-N,N-dimethylacrylamide) and poly(styrene-co-4-vinylpyridine). Thermochim. Acta 483, 49-54.
Farmer, V.C., 1974. The infrared spectra of minerals, Mineralogical society, London.
Ghaffar, A.M.E.A., 2002, Development of a biodegradable material based on Poly(3-hydroxybutyrate) PHB, In, Martin-Luther University, Wittenberg, pp. 115.
Ghosh, I., Jain, R.K., Glasser, W.G., 1999. Multiphase materials with lignin. XV. Blends of cellulose acetate butyrate with lignin esters. J. Appl. Polym. Sci. 74, 448-457.
Grassie, N., Murray, E.J., Holmes, P.A., 1984. The thermal degradation of poly(β-hydroxybutyric acid): Part 2--Changes in molecular weight. Polym. Degrad. Stab. 6, 95-102.
Grassie, N., Murray, E.J., Holmes, P.A., 1984. The thermal degradation of poly(β-hydroxybutyric acid): Part 3--The reaction mechanism. Polym. Degrad. Stab. 6, 127-134.
Guo, L., Sato, H., Hashimoto, T., Ozaki, Y., 2010. FT-IR study on hydrogen-bonding interactions in biodegradable polymer blends of poly(3-hydroxybutyrate) and pol(4-vinylphenol). Macromolecules 43, 3897-3907.
Hablot, E., Bordes, P., Pollet, E., Avérous, L., 2008. Thermal and thermo-mechanical degradation of poly(3-hydroxybutyrate)-based multiphase systems. Polym. Degrad. Stab. 93, 413-421.
129
Ikejima, T., Cao, A., Yoshie, N., Inoue, Y., 1998. Surface composition and biodegradability of poly(3-hydroxybutyric acid)/poly(vinyl alcohol) blend films. Polym. Degrad. Stab. 62, 463-469.
Kumagai, Y., Doi, Y., 1992. Enzymatic degradation and morphologies of binary blends of microbial poly(3-hydroxy butyrate) with poly(ε-caprolactone), poly(1,4-butylene adipate and poly(vinyl acetate). Polym. Degrad. Stab. 36, 241-248.
Li, S.D., He, J.D., Yu, P.H., Cheung, M.K., 2003. Thermal degradation of poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) as studied by TG, TG–FTIR, and Py–GC/MS. J. Appl. Polym. Sci. 89, 1530-1536.
Lim, S.P., Gan, S.N., Tan, I., 2005. Degradation of medium-chain-length polyhydroxyalkanoates in tropical forest and mangrove soils. Appl. Biochem. Biotech. 126, 23-33.
Mousavioun, P., Doherty, W.O.S., George, G., 2010. Thermal stability and miscibility of poly(hydroxybutyrate) and soda lignin blends. Ind. Crops Prod. 32, 656-661.
Pandey, K.K., 1999. A study of chemical structure of soft and hardwood and wood polymers by FTIR spectroscopy. J. Appl. Polym. Sci. 71, 1969–1975.
Pizzoli, M., Scandola, M., Ceccorulli, G., 1994. Crystallization kinetics and morphology of poly(3-hydroxybutyrate)/cellulose ester blends. Macromolecules 27, 4755-4761.
Scott, G., 2002, Degradable polymers, principles and application, In, Kluwer academic publisher, Dordrecht.
Sticklen, M.B., 2008, Mariam Sticklen's Home Page, In: Biofuel & Biopharmaceutical Crop Genetic Engineering Lab, Dept. of Crop and Soil science, East Lansing.
Weihua, K., He, Y., Asakawa, N., Inoue, Y., 2004. Effect of lignin particles as a nucleating agent on crystallization of poly(3-hydroxybutyrate). J. Appl. Polym. Sci. 94, 2466-2474.
Woolnough, C.A., Yee, L.H., Charlton, T., Foster, L.J.R., 2010. Environmental degradation and biofouling of ‘green’ plastics including short and medium chain length polyhydroxyalkanoates. Polym. Int. 59, 658-667.
Wu, C.S., 2006. Assessing biodegradability and mechanical, thermal, and morphological properties of an acrylic acid-modified poly(3-hydroxybutyric acid)/wood flours biocomposite. Journal of Applied Polymer Science 102, 3565-3574.
Xing, P., Dong, L., An, Y., Feng, Z., Avella, M., Martuscelli, E., 1997. Miscibility and crystallization of poly(β-hydroxybutyrate) and poly(p-vinylphenol) blends. Macromolecules 30, 2726-2733.
Yoshie, N., Azuma, Y., Sakurai, M., Inoue, Y., 1995. Crystallization and compatibility of poly(vinyl alcohol)/poly(3-hydroxybutyrate) blends: influence of blend composition and tacticity of poly(vinyl alcohol). J. Appl. Polym. Sci. 56, 17-24.
Zhang, L., Deng, X., Zhao, S., Huang, Z., 1997. Biodegradable polymer blends of poly(3-hydroxybutyrate) and poly(DL-lactide)-co-polyethylene glycol. J. Appl. Polym. Sci. 65, 1849-1856.
130
Zhang, L., Xiong, C., Deng, X., 1996. Miscibility, crystallization and morphology of poly(β-hydroxybutyrate)/poly(d,l-lactide) blends. Polymer 37, 235-241.
131
CHAPTER 6
Thermal stabil i ty and miscibil i ty of
poly(hydroxybutyrate) and methanol-
soluble soda l ignin blends
Payam Mousaviouna, William O.S. Dohertya, Graeme A. Georgeb and Peter
Halleyc a Sugar Research and Innovation, Centre for Tropical Crops and Biocommodities, Queensland University of Technology, GPO Box 2434, Brisbane, Australia. b School of Science and Technology, Queensland University of Technology, GPO Box 2434, Brisbane, Australia. c Centre High Performance Polymers (CHPP), AIBN, St Lucia, The University of Queensland, QLD 4072, Brisbane, Australia
Published in 10th AIChE meeting, Salt Lake City, UT, USA, November 2010
Research Students Centre, Level 4, 88 Musk Avenue, Kelvin Grove Campus, GPO Box 2434. Brisbane QLD 4001 Ph: +61 7 3138 4475 or 3138 5306 e-mail [email protected]
http://www.rsc.qut.edu.au/studentsstaff/ Correct as at: 7-6-10
Suggested Statement of Contribution of Co-Authors for
Thesis by Published Paper The authors listed below have certified* that: 1. they meet the criteria for authorship in that they have participated in the conception, execution, or
interpretation, of at least that part of the publication in their field of expertise; 2. they take public responsibility for their part of the publication, except for the responsible author
who accepts overall responsibility for the publication; 3. there are no other authors of the publication according to these criteria; 4. potential conflicts of interest have been disclosed to (a) granting bodies, (b) the editor or
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Australasian Digital Thesis database consistent with any limitations set by publisher requirements.
In the case of this chapter: Publication title and date of publication or status: Environmental degradation of soda lignin/PHB blends”, Polymer Degradation and Stability, 2011.
Contributor Statement of contribution* Payam
Mousavioun Wrote the manuscript, Experimental design, Conducted experiments, Data analysis.
Signature
Date
Graeme A. George
Aided experimental design, Data analysis.
William O.S. Doherty
Data analysis.
Principal Supervisor Confirmation I have sighted email or other correspondence from all Co-authors confirming their certifying authorship. _______________________ ____________________ ______________________ Name Signature Date
132
Abstract- Poly(3-hydroxybutyrate), PHB is a biodegradable and biocompatible
polymer generally produced by algae and bacteria. The main disadvantages of
PHB include: (a) prohibitive cost, (b) poor processability, and (c) thermal
instability during processing. Lignin (obtained from sugarcane fibre) has been
blended with PHB to ascertain improvements in PHB properties. The properties
of the blends were investigated by differential scanning calorimetry (DSC),
thermogravimetry analysis (TGA), scanning electron microscopy (SEM) and
Fourier transform infrared spectroscopy (FT-IR) over the entire range of
composition. The addition of methanol-soluble lignin increases the thermal
stability of PHB over a wide temperature range. A single glass transition
temperature (Tg), which depicts miscibility, was obtained for blends containing
up to 40 wt% lignin. At up to 30 wt% lignin, the experimental data fitted the
Gordon-Taylor and Kwei models. The Tg results correlate with the SEM and
FT-IR data. The FT-IR data show that the miscibility of the blends is probably
associated with specific hydrogen bonding interactions between the reactive
functional groups in lignin and the carbonyl groups of PHB.
6.1. I ntroduct ion Polyhydroxyalkanoates (PHAs) are a class of environmentally friendly natural
polymers (Verhoogt et al., 1994). Polyhydroxybutyrate (PHB) is a member of
this class of polymers. PHB is insoluble in many solvents and has good barrier
properties towards water, oxygen and carbon dioxide (Ghaffar, 2002). It is
readily broken down, with the aid of enzymes, to water and carbon dioxide.
These properties, combined with PHB’s potential for sustainable usage, makes it
a potential commodity material in the packaging industry.
The reasons why the potential of PHB has not been fully utilised, apart from its
prohibitive cost, are its stiff and brittle nature and its thermal instability during
processing. The crystal structure and crystallisation conditions are responsible
for these thermo-mechanical properties. PHB undergoes secondary nucleation at
an ambient temperature because of its low glass transition temperature (Tg) and it
possesses a low nucleation density resulting in the formation of large spherulites
(Barham and Keller, 1986). The spherulites contain crazes, and splitting occur
around the centre of these crazes, hence producing a significant structural weak
point (Mahendrasingam et al., 1995). PHB undergoes thermal degradation and
133
depolymerisation at temperatures close to its melting point and degradation is
further enhanced by high shear rates during melt processing and extrusion. One
approach to improve PHB’s properties is through blending (Antunes and
Felisberti, 2005, Chiu et al., 2001). Many polymer components in blends have
been found to be miscible or partially miscible on the basis of specific hydrogen-
bonding interactions due to the presence of functional groups (Kuo et al., 2002,
Kuo and Chang, 2001, Sixun et al., 2003, Yong et al., 2001, Yoshie et al., 1995,
Zheng and Mi, 2003). Lignin is an amorphous macromolecule composed of
phenylpropane repeat units that possesses aliphatic and aromatic hydroxyl
groups as well as carboxylic acid groups. These interacting functional groups, as
well as the amorphous nature of lignin, make it a good candidate for blending
with PHB. Limited studies have been carried out on PHB and lignin blends.
Ghosh et al. (2000) and Ghosh (1998) prepared blends (from the melt and
solution) of PHB, polyhydroxybutyrate-hydroxyvalerate (PHBV), cellulose
acetate butyrate with hardwood organosolv lignin and hardwood organosolv
lignin ester. The organosolv lignin and its butyrate derivative were found to
have a high degree of miscibility with PHB, and lignin was shown to inhibit and
retard PHB crystallisation. The source from which the lignin is obtained and its
method of extraction have a strong bearing on its properties (Lora and Glasser,
2002). Thus, in this work the thermal stability and miscibility between PHB and
methanol-soluble fraction of soda lignin was evaluated using TGA, DSC, SEM
and FT-IR.
6.2. Exper imental
6.2.1. PHB
Bacterial PHB was obtained from Sigma Aldrich. The weight average molecular
weight, Mw, as determined by gel permeation chromatography is 440,000 g mol-1
while the number average molecular weight, Mn, is 260,000 g mol-1. The Tg of
the PHB is 4°C.
134
6.2.2. Lignin extraction
Bagasse was obtained from Mackay Sugar Mill in Queensland, Australia. It was
wet depithed (through a 4.2 mm screen) and then air dried. Lignin was extracted
from bagasse by the soda process using a 18.5 L Parr reactor (Model 4555, Par).
In this method, 1 kg of bagasse is reacted with about 10.5 L of 0.7 M - 1 M
NaOH. Once the reactor reached the operating temperature of 170°C, this
temperature was maintained for 1.5 h. After cooling, the liquid (black liquor)
was removed from the bottom of the reactor and sieved to remove fibrous
material. The procedure used to recover and purify the lignin has been described
elsewhere (Mousavioun and Doherty, 2010).
Lignin is a complex and heterogeneous mixture with a broad molecular weight
distribution. To fractionate the lignin, ~ 100 g and 250 mL diethyl ether (AR
grade, Merck) are added to a 1 L beaker. The beaker is covered and the mixture
is stirred for 20 min before being left to settle for 10 min. The diethyl ether is
then decanted into another container. The remaining solid is then subjected to
the same treatment. This is repeated until the supernatant diethyl ether is a light
yellow colour when decanted. The lignin residue is allowed to dry before this
process is repeated using AR grade methanol (supplied by Merck) in place of
ether. The methanol soluble lignin (ML) was recovered using the rotary
evaporator to evaporate the solvent followed by filtration to recover the solid
lignin. The solid was then dried to a constant weight at 100°C for 2 h. The
amount of lignin recovered by this process was 64 wt% of the original starting
lignin material.
Details of the analytical procedures used for lignin characterisation (i.e., ash
analysis, sugar analysis, functional group analysis, molecular weight
determination) have been described by Mousavioun and Doherty (2010).
Table 6-1 gives the composition of ML. The purity of the lignin (98.4 wt%) is
comparable to organosolv lignin (96 wt%) (Mousavioun and Doherty, 2010).
Xylan is the highest proportion of the sugars associated with lignin. The number
average molecular weight (Mn) of the lignin is 2380, while the weight average
molecular weight (Mw) is 2670. The polydispersity (i.e. ratio of Mw to Mn) of
the lignin is 1.1 indicating that the lignin polymer consists of molecules of
similar chain length.
135
Tab le 6 - 1 Cha ra cte r i sa t ion o f ML
Type of analysis wt%
Ash 1.0
Glucan 0.1
Xylan 0.5
Arabinan <0.1
Methoxy 11.7
Phenolic OH 1.5
Total OH 15.3
RCOOH 21.1
6.2.3. PHB/Lignin blends
ML/PHB blends with lignin contents from 10 wt% to 90 wt% were mixed in a
Haake mini lab twin screw mixer using the procedure reported by Ghaffar
(2002). To minimise PHB degradation, the temperature of the extruder was
maintained at 175°C for 2 min (Mousavioun and Doherty, 2010). The polymer
blends were extruded as strands then cooled and pelletised. The pellets were
stored in a desiccator to avoid moisture absorption.
6.2.4. Characterisation of blends
6.2.4.1. Differential scanning calorimetry (DSC)
Approximately 10 mg -15 mg of the sample was precisely weighed and then
encapsulated in an aluminium pan. The pan was then placed in a DSC-Q100
instrument and heated from 0°C to 200°C at a heating rate of 10°C min-1 (cycle
1). The test was performed in an atmosphere of nitrogen, which was injected at a
flow rate of 15 mL min-1. Samples were then cooled at a rate of
30°C min-1 to -10°C (cycle 2). Samples were then reheated to 200°C at a rate of
10°C min-1 (cycle 3). The plot obtained from this second heating run shows the
Tg as a step transition.
136
6.2.4.2. Thermogravimetric analysis
Approximately 10 mg of sample was weighed into an aluminium pan and
analysed by thermogravimetric analysis (TGA). Heating was at a rate of 10°C
min-1 and was performed from room temperature to approximately 800°C. The
test was performed in an atmosphere of nitrogen, which was injected at a flow
rate of 15 mL min-1. A curve of weight loss against temperature was constructed
from the data obtained by the instrument. A derivative of this curve (DTG) was
produced to indicate the temperatures at which maximum rates of weight loss
occurred.
6.2.4.3. Scanning electron microscopy (SEM)
The morphology of the ML/PHB blends was examined using a scanning electron
microscope, type FEI Quanta 200 Environmental SEM at an accelerating voltage
of 15 kV. For this examination the pellets were compression moulded between
two sheets of Teflon using an established procedure (Ghosh et al., 1999).
6.2.4.4. Fourier transform-Infrared spectroscopy (FT-IR)
Infrared (IR) spectra were collected using a Nicolet 870 Nexus Fourier transform
infrared (FT-IR) spectrometer equipped with a Smart Endurance single bounce
diamond ATR accessory (Nicolet Instrument Corp., Madison, WI). Spectra were
manipulated and plotted with the use of the GRAMS/32 software package
(Galactic Corp., Salem, NH). The spectrometer incorporated a KBr beam splitter
and a deuterated triglycine sulfate room temperature detector. Spectra were
collected in the spectral range 4000 to 525 cm-1, using 64 scans at 4 cm-1
resolution with a mirror velocity of 0.6329 cms-1. The measurement time for
each spectrum was around 60 s.
6.3. Resul ts and D iscuss ion The thermal decomposition curve for ML is shown in Figure 6-1. The first
weight loss occurring at ~175°C is associated with water loss. The second
weight loss (i.e. the shoulder) with a peak maximum at 285°C is mainly
associated with hemicellulose (i.e. xylan) decomposition, while the peak at
335°C is associated with cellulose (i.e. glucan) and lignin decomposition
(Garcìa-Pèrez et al., 2001). At 420°C ~50 wt% of ML has decomposed. What is
worth noting in the result presented in Figure 6-1 is that lignin starts to degrade
at ~184°C and that its degradation is complex constituting of several processes.
137
PHB, on the other hand, appears to have two main overall degradation steps as
shown in Figure 6-2.
Figure 6-1 TGA/DTG curve of ML performed under nitrogen atmosphere.
Figure 6-2 TGA/DTG curve of PHB performed under nitrogen
atmosphere.
Figure 6-3 shows the integral thermogravimetric curves for ML/PHB blends with
those of ML and PHB included for comparison. The degradation of ML/PHB
blends occurs in several more stages than PHB, suggesting blending PHB with
ML has completely changed the decomposition profile of PHB. As shown in
Figure 6-3, inset, the decomposition temperature at which the material has
138
reached 5 wt% degradation, or (T0) of PHB increases up to 50 wt% lignin.
Thereafter, the T0 decreases with lignin addition. Figure 6-3 also shows that the
temperature at the maximum rate of weight loss of PHB decreases with the
addition of lignin. The degradation of pure PHB is almost complete by ~280°C,
whereas the weight loss for the blends is less than 85 wt%. The results from the
TGA study, therefore, show that overall the addition of ML increases the thermal
stability of PHB.
Figure 6-3 The integral thermogravimetric curves for PHB, ML and ML-PHB blends.
The most accepted parameter to assess polymer miscibility is the Tg. A single Tg
of a blend implies complete miscibility between the amorphous fractions of the
polymer components, whose value is an average of the individual Tg of the
polymer components. Two or more Tg’s suggest that the degree of miscibility is
restricted. Most miscible polymers display a single Tg whose value is dependent
on the proportion of the individual components (Fox, 1956). Figure 6-4
illustrates the Tgs of the lignin/PHB blends. A single Tg is obtained up to a ML
content of 40 wt%, thereafter there are two Tgs. The Tg results therefore give an
indication of miscibility between PHB and ML at lignin contents up to 40 wt%.
139
The exothermic peak at ~75°C (for 50 wt% and 70 wt%) is associated with the
cold crystallisation temperature of PHB (Ghaffar, 2002). The absence of this
peak in the other blends is not known and is worth further investigation.
Figure 6-4 DSC curves of ML/PHB blends (refer to Figure 4-5)
Figure 6-4 also shows that the Tg of the PHB component of the blends increases
with increase in ML content. Similar results were obtained by Ghosh and co-
workers (1999, 2000) for organosolv lignin/PHB blends, though the values
obtained in the present study were slightly higher (Figure 6-4). This could be
related to the method of preparation, differences in the PHB source, or the lignin
type as soda pulping generally increases the carboxylic acid and hydroxyl
contents of lignins relative to organosolv pulping (Gosselink et al., 2004).
We evaluated the Tg data using the well-known Fox (1956), Gordon-Taylor
(Schneider, 1988) and Kwei (Lin et al., 1989) equations, to obtain a better idea
of interactions between PHB and ML. These equations are:
Fox equation: �Op7qi_@r8 2 sL
Op,L3 sM
Op,M (6-1)
Gordon-Taylor equation: 9t7qi_@r8 27sLOp,L���csMOp,M8
7sL���csM8 (6-2)
Kwei equation: 9t7qi_@r8 27sLOp,L���sMOp,M8
7sL���sM83 yu�uR (6-3)
where Tz,� {| R and w� {| R are glass transition temperatures of the pure
components and their corresponding weight fractions, respectively. K��, K� and
q are adjustable parameters.
140
As shown in Figure 6-5, ML/PHB blends up to 30 wt% lignin fit to the Gordon-
Taylor model with a KGT value of 3.34. These blends also fit the Kwei model
with Kw value of 0.1 and q having a value of 15. The positive value of q and a
reasonable KGT value indicate some interactions exist between OH groups of
lignin and the carbonyl groups of PHB for the blends containing up to 30 wt%
lignin (ElMiloudi et al., 2009). It should be pointed out that these interaction
parameters are lower than those obtained for soda lignin in a previous study
(Mousavioun et al., 2010). One point of difference between ML and the soda
liginin of previous study is that the soda lignin contained 4 times the amount of
phenolic OH groups present in ML.
Figure 6-5 Tgs of PHB and the blends versus ML content.
Figures 6-6, 6-8 and 6-8 illustrate typical SEM images of blends. For blends
containing 10 wt% and 30 wt% lignin, there was no apparent phase separation,
whereas for the blends with 50 wt% of lignin and higher, phase separation was
observed. Thus, the SEM data confirm the Tg data.
141
Figure 6-6 SEM image of ML/PHB blend containing 10 wt% ML.
Figure 6-7 SEM image of ML/PHB blend containing 30 wt% ML.
Figure 6-8 SEM image of ML/PHB blend containing 50 wt% ML.
Figure 6-9 shows the FT-IR spectra from 1800 cm-1 to 1620 cm-1 of the carbonyl
stretching region of PHB and ML/PHB blends. PHB spectrum exhibits main two
peaks, these are at 1733 cm-1 and 1722 cm-1, though the first peak at 1733 cm-1 is
more of a shoulder to the main peak at 1722 cm-1. The peak at 1733 cm-1 is
associated with the amorphous component of PHB, the peak at ~1722 cm-1 is
associated with the crystalline component of PHB (in its preferred
142
conformation), and the peak at 1697 cm-1 is associated with hydrogen-bonded
carbonyl (Guo et al., 2010). The band at 1685 cm-1 has been reported to be a
crystalline band, although its origin is not known (Guo et al., 2010).
Figure 6-9 FT-IR spectra of the carbonyl stretching region of PHB and
ML/PHB blends.
Tab le 6 - 2 Pea k asso c ia ted w i th c ry sta l l i ne po r t ion o f PHB
Lignin content (wt%) Wavenumber at Max. transmission (cm-1) 0 1722 10 1718 30 1720 40 1720 50 1720 70 1722 80 1722 90 1722
The shift to a lower wavenumber is indicative of hydrogen bonding interactions
(Barsbay and Güner, 2007). As shown in Figure 6-9 (and Table 6-2), for blends
containing 10 wt%, 30 wt%, 40 wt% and 50 wt% ML, there is a small but
definitive shift (2 cm-1to 4 cm-1) to a lower wavenumber relative to the PHB
peak of 1722 cm-1. This implies that the reactive functional groups of ML are
engaged in hydrogen bonding interactions with the carbonyl oxygen in PHB as
has been reported in a previous study (Mousavioun et al., 2010). This explains
143
the compatibility obtained between PHB and lignin for the blends containing up
to 50 wt% lignin. The reason why there were no differences in some of the
wavenumber shifts between these blends containing different proportions of
lignin is not known.
Figure 6-9 also shows that for the PHB band at 1733 cm-1, there is probably a
slight shift to a lower wavenumber (~ 4 cm-1) for the 10 wt% and 30 wt% blends.
Although this band is of less intensity compared the main band at 1722 cm-1 it
shows some favourable interactions between the amorphous part of PHB and
lignin. The slight shift to a higher wavenumber for the other blends may also be
linked to some sort of association between ML and PHB.
6.4. Conclus ion The addition of lignin to PHB has been found to improve the overall thermal
stability of PHB. For blends containing up to 50 wt% lignin, the addition of
lignin raised the initial decomposition temperature i.e. T0 of PHB by a few
degrees. Glass transition temperature and microscopy studies indicated
miscibility with blends containing 10 wt% - 40 wt%. At up to 30 wt% lignin, the
experimental data fitted the Gordon-Taylor and Kwei models. The
intermolecular interactions between the two polymer components were found to
be due to hydrogen bonding formation between their functional groups.
144
6.5. References Antunes, M.C.M., Felisberti, M.I., 2005. Blends of poly(hydroxybutyrate) and
poly(ε-caprolactone) obtained from melting mixture. Polym. Sci. Technol. 15, 134-138.
Barham, P.J., Keller, A., 1986. The relationship between microstructure and mode of fracture in polyhydroxybutyrate. J. Polym. Sci. Part B: Polym. Phys. 24, 69-77.
Barsbay, M., Güner, A., 2007. Miscibility of dextran and poly(ethylene glycol) in solid state: Effect of the solvent choice. Carbohyd. Polym. 69, 214-223.
Chiu, H.J., Chen, H.L., Lin, J.S., 2001. Crystallization induced microstructure of crystalline/crystalline poly(vinylidenefluoride)/poly(3-hydroxybutyrate) blends probed by small angle X-ray scattering. Polymer 42, 5749-5754.
ElMiloudi, K., Djadoun, S., Sbirrazzuoli, N., Geribaldi, S., 2009. Miscibility and phase behaviour of binary and ternary homoblends of poly(styrene-co-acrylic acid), poly(styrene-co-N,N-dimethylacrylamide) and poly(styrene-co-4-vinylpyridine). Thermochim. Acta 483, 49-54.
Fox, T.G., 1956. Influence of diluent and of copolymer composition on the glass temperature of a polymer system. Bull. Am. Phys. Soc. 2, 123.
Garcìa-Pèrez, M., Chaala, A., Yang, J., Roy, C., 2001. Co-pyrolysis of sugarcane bagasse with petroleum residue. Part I: thermogravimetric analysis. Fuel 80, 1245-1258.
Ghaffar, A.M.E.A., 2002, Development of a biodegradable material based on Poly(3-hydroxybutyrate) PHB, In, Martin-Luther University, Wittenberg, pp. 115.
Ghosh, I., 1998, Blends of biodegradable thermoplastics with lignin esters, In, Virginia Polytechnic Institute and State University, VA, pp. 139.
Ghosh, I., Jain, R.K., Glasser, W.G., 1999. Multiphase materials with lignin. XV. Blends of cellulose acetate butyrate with lignin esters. J. Appl. Polym. Sci. 74, 448-457.
Ghosh, I., Jain, R.K., Glasser, W.G., 2000. Multiphase materials with lignin. Part 16. Blends of biodegradable thermoplastics with lignin esters. ACS Symp. Ser. 742, 331-350.
Gosselink, R.J.A., Abächerli, A., Semke, H., Malherbe, R., Käuper, P., Nadif, A., van Dam, J.E.G., 2004. Analytical protocols for characterisation of sulphur-free lignin. Ind. Crops Prod. 19, 271-281.
Guo, L., Sato, H., Hashimoto, T., Ozaki, Y., 2010. FTIR study on hydrogen-bonding interactions in biodegradable polymer blends of poly(3-hydroxybutyrate) and pol(4-vinylphenol). Macromolecules 43, 3897-3907.
Kuo, S.W., Chan, S.C., Chang, F.C., 2002. Miscibility enhancement on the immiscible binary blend of poly(vinyl acetate) and poly(vinyl pyrrolidone) with bisphenol A. Polymer 43, 3653-3660.
Kuo, S.W., Chang, F.C., 2001. Effects of Copolymer Composition and Free Volume Change on the Miscibility of Poly(styrene-co-vinylphenol) with Poly(ε-caprolactone). Macromolecules 34, 7737-7743.
Lin, A.A., Kwei, T.K., Reiser, A., 1989. On the physical meaning of the Kwei equation for the glass transition temperature of polymer blends. Macromolecules 22, 4112-4119.
145
Lora, J.H., Glasser, W.G., 2002. Recent Industrial Applications of Lignin: A Sustainable Alternative to Nonrenewable Materials. J. Polym. Environ. 10, 39-48.
Mahendrasingam, A., Martin, C., Fuller, W., Blundell, D.J., MacKerron, D., Rule, R.J., Oldman, R.J., Liggat, J., Riekel, C., Engstrom, P., 1995. Microfocus X-ray Diffraction of Spherulites of Poly-3-hydroxybutyrate. J. Synchr. Rad. 2, 308-312.
Mousavioun, P., Doherty, W.O.S., 2010. Chemical and thermal properties of fractionated bagasse soda lignin. Ind. Crops Prod. 31, 52-58.
Mousavioun, P., Doherty, W.O.S., George, G., 2010. Thermal stability and miscibility of poly(hydroxybutyrate) and soda lignin blends. Ind. Crops Prod. 32, 656-661.
Schneider, H.A., 1988. The Gordon-Taylor equation. Additivity and interaction in compatible polymer blends. Die Makromolekulare Chemie 189, 1941-1955.
Sixun, Z., Qipeng, G., Chi-Ming, C., 2003. Epoxy resin/poly(ɛ-caprolactone) blends cured with 2,2-bis[4-(4-aminophenoxy)phenyl]propane. II. Studies by Fourier transform infrared and carbon-13 cross-polarization/magic-angle spinning nuclear magnetic resonance spectroscopy. J. Polym. Sci., Part B: Polym. Phys. 41, 1099-1111.
Verhoogt, H., Ramsay, B.A., Favis, B.D., 1994. Polymer blends containing poly(3-hydroxyalkanoate)s. Polymer 35, 5155-5169.
Yong, H., Naoki, A., Yoshio, I., 2001. Blend of Poly(ɛ-caprolactone) and 4,4'-Thiodiphenol: Hydrogen Bond Formation and Some Solid Properties. Macromol. Chem. Phys. 202, 1035-1043.
Yoshie, N., Azuma, Y., Sakurai, M., Inoue, Y., 1995. Crystallization and compatibility of poly(vinyl alcohol)/poly(3-hydroxybutyrate) blends: influence of blend composition and tacticity of poly(vinyl alcohol). J. Appl. Polym. Sci. 56, 17-24.
Zheng, S., Mi, Y., 2003. Miscibility and intermolecular specific interactions in blends of poly(hydroxyether of bisphenol A) and poly(4-vinyl pyridine). Polymer 44, 1067-1074.
146
CHAPTER 7
Conclusions and Further Research
147
7.1. Conclus ions
In this thesis, the advantages and disadvantages of blending lignin with PHB
have been studied. The properties of the lignin/PHB blends that were studied
are:
� Thermal properties and miscibility
� Thermophysical and rheological properties
� Environmental degradation
� Thermal properties of PHB blends with different types of lignin
7.1.1. Thermal properties and miscibility study.
In this study, lignin was found to increase the overall thermal stability of the
PHB/lignin blend, although it reduces the initial onset temperature of PHB
degradation. Thermal analyses (TGA and DSC) indicate that it is the
intermolecular interaction between PHB and lignin which causes miscibility
within a range of blends. One of the fundamental outcomes of these
investigations is the evaluation of the range of miscibility of these two polymers
and thermal analyses revealed that 40 wt% lignin is the highest amount of lignin
which gives a miscible blend. There was a significant difference between the
properties of miscible and immiscible blends reflected in the thermal, rheological
and environmental degradation properties. One of the factors which control
miscibility is believed to be hydrogen bonding between carbonyl groups of PHB
and hydroxyl groups of lignin.
7.1.2. Thermophysical and rheological properties of lignin/PHB
blends
The mechanical properties of PHB are affected by the high degree of crystallinity
(62 %) and the Tg of 4°C. PHB has a low concentration of nucleation sites so it
has relatively big crystals which make it brittle and susceptible to secondary
crystallisation. Lignin has been shown to reduce the bulk crystallinity of PHB
up to 65% (see Table 4-4). Another benefit which lignin provides to PHB during
blending is a reduction in the melting temperature and so enables PHB to be
148
processed at a lower temperature. Decreasing the processing temperature not
only reduces the risk of thermal degradation of PHB, but also saves energy.
A low concentration of lignin is also found to plasticise PHB. In the miscible
region, lignin lowers by up to 10 times the lignin/PHB blend melt viscosity
which facilitates the processing of PHB and saves energy.
7.1.3. Environmental investigation of lignin/PHB blends
Investigations of lignin/PHB blends on soil burial for up to 12 months showed
lignin does not improve the biodegradation properties of PHB. Lignin not only,
even in low concentration, inhibits the biodegradation of PHB, it decreases the
rate of degradation as burial time is increased. Surface composition analysis
using XPS show a presence of both PHB and lignin on the surface of film
samples. The analysis also revealed the presence of biofilms on the buried films.
The presence of biofilms is evidence of biodegradation. In a future study it is
worth to investigate the antimicrobial effect of lignin on lignin/PHB blends.
7.1.4. Thermal properties of PHB blends with different types of lignin
According to chemical analyses in this study, soda lignin (SL) has a far higher
concentration of phenolic hydroxyl group with lower content of carboxylic acid
and methoxyl groups compared to ML (see Table 2-3). Also, modelling results
based on the Gordon-Taylor equation showed stronger hydrogen bonding in
SL/PHB blends 7K�� 2 22.08 compared with ML/PHB 7K�� 2 3.348. Therefore, the conclusion is that the phenolic hydroxyl group could make a
stronger contribution in hydrogen bonding. The T0 values of ML/PHB blends
were higher than the T0 values of soda lignin/PHB blends. This may be because
of the proportion of xylan in the composite (see Table 2-4). Xylans are known to
decompose at lower temperatures than cellulose and lignin.
Tg results of ML/PHB blends indicated that blends containing up to 40 wt% ML
are miscible with PHB. The similar results were obtained for soda lignin/PHB
blends (section 1.3.3). FT-IR spectra showed that for blends up to 50 wt% ML,
there was a small but definitive shift to lower wavenumbers, indicating hydrogen
149
bonding interactions. The similarities between the results and those of
lignin/PHB blends indicated that the differences observed in the composition of
lignin functional groups were not significant to influence the glass transition
temperature of lignin/PHB blends derived from the two lignin types.
7.2. Future Research
The opportunities for future related research can be classified in the following
areas:
� Study of molecular structure of PHB during processing with lignin
� Modelling the viscoelasticity of lignin/PHB blends
� Study of antimicrobial effect of lignin
� Study of mechanical properties of lignin/PHB blends
7.2.1. Study of molecular structure of PHB during blend processing
In the processing of lignin/PHB blends, PHB is sensitive to thermal degradation.
The degradation temperature of PHB is close to its melting point. An
investigation for monitoring the molecular structure of lignin/PHB blend while
processing could be linked with the proposed methods to evaluate the kinetics of
the degradation reaction of PHB. The FT-IR monitoring of the extruder chamber
for the lignin/PHB blend could be a good approach to detect changes in
molecular structure of PHB and lignin/PHB blends. A near infrared spectroscopy
(NIRS) method is available (Siesler, et al., 2007) for real-time monitoring of the
processing in the Haake Minilab extruder and this could be adapted for these
studies.
7.2.2. Modeling the viscoelasticity of lignin/PHB blends
Data on the complex viscosity of lignin/PHB blends at different temperatures,
lignin content and frequencies could be used to develop a model that can be
used to provide processing conditions for different blend compositions. For
creating such a model, it is essential to trial a frequency sweep of the complex
150
viscosity of lignin/PHB blends at different temperatures. However, the sensitivity
of PHB to degradation in such close range to its melting point makes this
correlation hard. Using FT-IR detection during the rheological study could be
useful to detect when degradation is occurring.
7.2.3. Study of antimicrobial effect of lignin
An investigation of the radical scavenging activity of lignin could clarify why
lignin protected PHB from biodegradation. Lignin is known to be a natural
antioxidant (Dizhbite, et al., 2004) with a variety of functional groups containing
oxygen (for example hydroxyl and carboxylic acid) which could play a
considerable role in antibacterial and antifungal activity (Nada, et al., 1989).
Based on the outcomes of this thesis, lignin resisted the degradation of PHB even
on the surface of buried films which were exposed to the soil. A more detailed
laboratory-based microbiological study could help to understand this.
7.2.4. Study of mechanical properties of lignin/PHB blends
Utilizing lignin in low concentration leads to miscible blends with PHB. Also,
lignin in higher amounts acts as a filler in lignin/PHB blends and moreover,
lignin affects the bulk crystallinity of lignin/PHB blends both of which alter the
mechanical properties of PHB. Both miscible and immiscible blends of
lignin/PHB need to be investigated in terms of mechanical properties such as
tensile strength and elongation at break.
151
7.3. References
Dizhbite, T., Telysheva, G., Jurkjane, V., Viesturs, U., 2004. Characterization of
the radical scavenging activity of lignins--natural antioxidants. Bioresource Technol. 95, 309-317.
Nada, A.M.A., El-Diwany, A.I., Elshafei, A.M., 1989. Infrared and antimicrobial studies on different lignins. Acta Biotechnologica 9, 295-298.
Siesler, H.W., Ozaki, Y., Kawata, S., Heise, H.M., 2007. Near-Infrared Spectroscopy, Wiley-VCH Verlag GmbH.
Research Students Centre, Level 4, 88 Musk Avenue, Kelvin Grove Campus, GPO Box 2434. Brisbane QLD 4001 Ph: +61 7 3138 4475 or 3138 5306 e-mail [email protected]
http://www.rsc.qut.edu.au/studentsstaff/ Correct as at: 7-6-10
Suggested Statement of Contribution of Co-Authors for
Thesis by Published Paper The authors listed below have certified* that: 1. they meet the criteria for authorship in that they have participated in the conception, execution, or
interpretation, of at least that part of the publication in their field of expertise; 2. they take public responsibility for their part of the publication, except for the responsible author
who accepts overall responsibility for the publication; 3. there are no other authors of the publication according to these criteria; 4. potential conflicts of interest have been disclosed to (a) granting bodies, (b) the editor or
publisher of journals or other publications, and (c) the head of the responsible academic unit, and 5. they agree to the use of the publication in the student’s thesis and its publication on the
Australasian Digital Thesis database consistent with any limitations set by publisher requirements.
In the case of this chapter: Publication title and date of publication or status: Environmental degradation of soda lignin/PHB blends”, Polymer Degradation and Stability, 2011.
Contributor Statement of contribution* Payam
Mousavioun Wrote the manuscript, Experimental design, Conducted experiments, Data analysis.
Signature
Date
Graeme A. George
Aided experimental design, Data analysis.
William O.S. Doherty
Data analysis.
Principal Supervisor Confirmation I have sighted email or other correspondence from all Co-authors confirming their certifying authorship. _______________________ ____________________ ______________________ Name Signature Date
152
APPENDIX 1
Thermal decomposition of bagasse.
Effect of different sugarcane cultivars
Vanita, R. Maligera, William O.S. Dohertya, Ray L. Frostb and Payam
Mousaviouna
a Sugar Research and Innovation, Centre for Tropical Crops and
Biocommodities, Queensland University of Technology, GPO Box 2434,
Brisbane, Australia. b Inorganic Materials Research Program, School of Physical & Chemical
Sciences, Queensland University of Technology, GPO Box 2434, Brisbane,
Australia
Published in the Journal of Industrial & Engineering Chemistry Research, Vol
50, Page 791, 2011
Research Students Centre, Level 4, 88 Musk Avenue, Kelvin Grove Campus, GPO Box 2434. Brisbane QLD 4001 Ph: +61 7 3138 4475 or 3138 5306 e-mail [email protected]
http://www.rsc.qut.edu.au/studentsstaff/ Correct as at: 7-6-10
Suggested Statement of Contribution of Co-Authors for
Thesis by Published Paper The authors listed below have certified* that: 1. they meet the criteria for authorship in that they have participated in the conception, execution, or
interpretation, of at least that part of the publication in their field of expertise; 2. they take public responsibility for their part of the publication, except for the responsible author
who accepts overall responsibility for the publication; 3. there are no other authors of the publication according to these criteria; 4. potential conflicts of interest have been disclosed to (a) granting bodies, (b) the editor or
publisher of journals or other publications, and (c) the head of the responsible academic unit, and 5. they agree to the use of the publication in the student’s thesis and its publication on the
Australasian Digital Thesis database consistent with any limitations set by publisher requirements.
In the case of this chapter: Publication title and date of publication or status: Thermal stability and miscibility of poly(hydroxybutyrate) and methanol-soluble soda lignin blends”, presentation in 10th AIChE meeting, Salt Lake City, UT, USA, November 2010. CD Rom.
Contributor Statement of contribution* Payam
Mousavioun Wrote part of the manuscript, Experimental design, Conducted experiments, Data analysis.
Signature
Date William O.S.
Doherty
Wrote the manuscript, Data analysis.
Graeme A. George Data analysis.
Peter Halley Data analysis
Principal Supervisor Confirmation I have sighted email or other correspondence from all Co-authors confirming their certifying authorship. _______________________ ____________________ ______________________ Name Signature Date
174
APPENDIX 2
Value-adding to cellulosic ethanol:
Lignin polymers
William O.S. DohertyA, Payam MousaviounA and Christopher M. FellowsB
A Centre for Tropical Crops and Biocommodities, Queensland University of Technology, GPO Box 2434, Brisbane, QLD 4000, Australia B Chemistry, School of Science and Technology, The University of New England, Armidale, NSW 2351, Australia
Published in Industrial Crops and Products, Vol 32, Page 259, 2011
175
Abstract- Lignocellulosic waste materials are the most promising feedstock for
generation of a renewable, carbon-neutral substitute for existing liquid fuels.
The development of value-added products from lignin will greatly improve the
economics of producing liquid fuels from biomass. This review gives an outline
of lignin chemistry, describes the current processes of lignocellulosic biomass
fractionation and the lignin products obtained through these processes and finally
outlines the current and potential value-added applications of these products, in
particular as components of polymer blends.
A.2.1. I ntroduc t ion Concern about the depletion of fossil fuel resources and climate change
attributed to anthropogenic carbon dioxide emissions is driving a strong global
interest in renewable, carbon-neutral energy sources and chemical feedstocks
derived from plant sources. Commercial products, which are capturing an
increasing share of the liquid fuel market, are esters of long-chain fatty acids
from plant oils (biodiesel) and ethanol from the enzymatic digestion and
fermentation of starch or sucrose. As an example of the use of biomass as a
chemical feedstock, a consortium led by Dupont is working to convert maize
starch to the monomer, 1,3-propandiol, using genetically modified Escherichia
coli (Caimi, 2004, Wehner et al., 2007). This monomer can then be used to
prepare poly(trimethylene terephthalate), a polyester which is traditionally
synthesised by the polycondensation of trimethylene glycol with either
terephthalic acid or dimethyl terephthalate (Kurian, 2005, Kurian and Liang,
2008).
Industrial production of fuels and feedstocks from plant sources has concentrated
on those sources that can be most readily and economically processed, such as
oil palm, sugarcane, and corn. However, these compete for arable land with
crops intended for human or animal consumption, putting upward pressure on
food prices and accelerating environmental degradation. For this reason, current
research efforts have concentrated on lignocellulosic biomass from sources that
do not compete with food crops: e. g., agricultural waste products, such as sugar
cane bagasse, wheat straw, rice stalk, cotton linters, and forest thinnings, or
novel crops that can be grown in environments too marginal for food production,
such as switchgrass and eucalypts (Sierra et al., 2008). In order for biomass to
176
be a sustainable source of liquid fuel, technologies are required to enable the
economic production of suitable compounds from these sources, the dry mass of
which consists primarily of a matrix of cellulose, hemicellulose, and lignin
intimately mixed on a microscopic scale.
Current research is focussed on increasing the effectiveness and reducing the
cost of cellulase and xylanase enzymes for cellulose and hemicellulose
saccharification, (Maki et al., 2009, Oehgren et al., 2007, Rattanachomsri et al.,
2009), developing enzymes capable of converting the range of sugars produced
by the digestion of hemicelluloses to ethanol, (Bettiga et al., 2009, Yano et al.,
2009) and improving the pre-treatment process for the fractionation of cellulose,
hemicellulose and lignin from biomass (Fox et al., 1987, Kim, 2009, Moxley,
2008). Whatever the means, for producing ethanol from lignocellulosic biomass,
large volumes of lignin will be produced. Current pilot plants producing ethanol
from lignocellulosic material use the residual lignin for energy generation,
sequester it as ‘biochar’ as a carbon sink, or must dispose of it as waste. The
viability of biofuel production would clearly be greatly enhanced by the
development of markets for lignin-derived products. Any value-added lignin
derived product will improve the economics of biomass conversion, while high-
volume bulk commodity applications will also address the problem of waste
lignin disposal. There are a number of physicochemical factors which suggest a
bright future for lignin-based products: (a) compatibility with a wide range of
industrial chemicals; (b) presence of aromatic rings providing stability, good
mechanical properties, and the possibility of a broad range of chemical
transformations; (c) presence of other reactive functional groups allowing facile
preparation of graft copolymers; (d) good rheological and viscoelastic properties
for a structural material; (e) good film-forming ability; (f) small particle size; and
(g) hydrophilic or hydrophobic character depending on origin, allowing a wide
range of blends to be produced (Mousavioun and Doherty, 2010).
The focus of this review is the preparation of possible value-added polymers
derived from the varieties of lignin likely to be generated in significant amounts
from the production of cellulosic ethanol.
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A.2.2. L ignin Struc ture Lignocellulose materials refer to plants that are composed of cellulose,
hemicellulose and lignin. The cellulose microfibrials (formed by ordered
polymer chains that contain tightly packed, crystalline regions) are embedded
within a matrix of hemicellulose and lignin (Figure 3-1). Covalent bonds
between lignin and the carbohydrates have been suggested to consist of benzyl
esters, benzyl ethers and phenyl glycosides (Smook, 2002).
Figure A.2-1 Cellulose strands surrounded by hemicellulose and lignin (Department of energys genomic, http://genomics.energy.gov, 1986)
Lignin is primarily a structural material to add strength and rigidity to cell walls
and constitutes between 15 wt% and 40 wt% of the dry matter of woody plants.
Lignin is more resistant to most forms of biological attack than cellulose and
other structural polysaccharides, (Akin and Benner, 1988, Baurhoo et al., 2008,
Kirk, 1971) and plants with a higher lignin content have been reported to be
more resistant to direct sunlight and frost (Miidla, 1980). In vitro, lignin and
lignin extracts have been shown to have antimicrobial and antifungal activity,
(Cruz et al., 2001) act as antioxidants, (Krizkova et al., 2000, Pan et al., 2006,
Ugartondo et al., 2008) absorb UV radiation, (Toh et al., 2005, Zschiegner,
1999) and exhibit flame-retardant properties (Reti et al., 2008).
178
Lignin is a cross-linked macromolecular material based on a phenylpropanoid
monomer structure (Figure A.2-2). Typical molecular masses of isolated lignin
are in the range 1,000 g mol-1 to 20,000 g mol-1, but the degree of polymerisation
in nature is difficult to measure, since lignin is invariably fragmented during
extraction and consists of several types of substructures which repeat in an
apparently haphazard manner. In this review the term ‘lignin’ will be used both
for the in vivo material and the various fractions isolated from living matter,
which invariably undergo some degree of chemical and physical change.
The monomer structures in lignin consist of the same phenylpropenoid skeleton,
but differ in the degree of oxygen substitution on the phenyl ring. The H-
structure (4-hydroxy phenyl) has a single hydroxy or methoxy group, the G-
structure (guaiacyl) has two such groups, and the S-structure (syringyl) has three
(Figure A.2-2). The polymerisation of the phenylpropanoid monomers is
initiated by oxidases or peroxidases. While the precise mechanism is obscure, it
is postulated that radical-radical combination of free radicals produced by
enzymatic dehydrogenation is the key reaction, either under enzymatic control
(Davin et al., 2008) or in a random ‘combinatorial’ manner (Ralph et al., 2004).
(a) (b) (c)
Figure A.2-2 Monolignol monomer species. (a) p-coumaryl alcohol (4-hydroxyl phenyl, H), (b) coniferyl alcohol (guaiacyl, G), (c) sinapyl alcohol (syringyl, S)
Both carbon-carbon and carbon-oxygen bonds between monomers are found in
lignin (Figure A.2-3). The most common functionality, accounting for about
half the bonds between monomers in lignin from most sources, is a carbon-
oxygen link between a p-hydroxy moiety and the β-end of the propenyl group (β-
OH
OH
OH
OH
OCH3 OH
OH
OCH3
OCH3
179
O-4) (Figure A.2-3a) (Chen, 1991, Ede and Kilpelaeinen, 1995, Kukkola et al.,
2004).
(a) (b) (c)
(d) (e) (f)
Figure A.2-3 Significant lignin linkage structures. (a) β-O-4, (b) αααα-O-4, (c) 5-5, (d) β-β, (e) 5-O-5, (f) β-5
The degree of cross-linking possible in lignin, and hence the rigidity of the
structure, is dependent on the degree of substitution. In softwoods, the G
OCH3
O
O
OCH3
OH OCH3
O
OCH3
O
OH
OCH3
O OO
CH3
O
O
OCH3
O
OCH3
OH
OH
OO
CH3
O OCH3
O
OCH3
O
OCH3
OH
180
structure is dominant, while hardwood lignins normally contain a mixture of S
and G structures with S in the majority, while H structures predominate in
lignins found in grasses (Wang et al., 2009).
Recent interest in lignin has been driven by the fact that it forms a large
proportion of the non-food biomass under consideration for the production of
renewable and carbon-neutral liquid fuels and chemical feedstocks. Separation
of cellulose from lignin is one of many technical hurdles which must be
overcome in order for biofuels to be economically produced from cellulose-
containing waste. While biotechnology allows plants to be modified to have a
larger cellulose: lignin ratio (Hu et al., 1999, Sticklen, 2008) and alter lignin
structure to produce lignins which can be more easily separated, (Lapierre et al.,
1999) these strategies will unavoidably run into limits imposed by plant
physiology and thus a significant volume of waste lignin is unavoidable.
A.2.3. L ignin Fract iona t ion Processes The extraction of lignin from lignocellulosic materials is conducted under
conditions where lignin is progressively broken down to lower molecular weight
fragments, resulting in changes to its physicochemical properties. Thus, apart
from the source of the lignin, the method of extraction will have a significant
influence on the composition and properties of lignin. The majority of lignin
extraction and delignification processes occur by either acid or base-catalysed
mechanisms. The chemistry of bond cleavage in lignin by these mechanisms has
been reviewed by Gratzl and Chen (2000).
A.2.3.1. Sulfite process
At present the main commercial source of lignin is from the pulp and paper
industry. The sulfite process which traditionally used to be the main pulping
technology involves the reaction of a metal sulfite and sulfur dioxide (Smook,
2002). The main reactions that take place during the pulping process are: (a) the
reaction between lignin and free sulfurous acid to form lignosulfonic acid, (b) the
formation of the relatively soluble lignosulfonates with the cations, Mg, Na or
NH4+, and (c) the fragmentation of the lignosulfonates. In addition to
lignosulfonates, degraded carbohydrates are also produced. The pulping
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reactions are usually conducted between 140°C and 160°C and the pH of the acid
sulfite process is between 1.5 and 2.0, while the bisulfite process is between pH
4.0 to 5.0 (Smook, 2002). The chemistry of the sulfide process has been
exhaustively reviewed by Wong (1980) and more recently by Alen (2000).
Several purification steps are required to obtain the lignosulfonate fraction with
high purity, including fermentation to convert the residual sugars to ethanol and
membrane fitration to reduce the metal ion content. The lignosulfonate
biopolymer is typically highly cross-linked, with ~5 wt% sulfur content, and
bears two types of ionising groups; sulfonates (pKa ≤ 2) and phenolic hydroxy
groups (pKa ~ 10). Because of the low pKa for the sulfonate groups,
lignosulfonates are water-soluble under most conditions. The physicochemical
properties of lignosulfonates are affected by the metal cation (Na or Ca) of the
sulfite salt used during the pulping process. Sodium sulfite produces more
extended lignin chains that are more suitable for use as dispersants, while
calcium sulfite produces more compact lignin, presumably due to a bridging
effect of chelating Ca2+. The sulfur content (5 wt%) of sulfite lignins is one of
the major factors restricting its use in speciality applications, and so most of its
lignin is currently used for energy generation.
The sulfite delignification process is an acid catalysed process in which there is
cleavage of the α-ether linkages and β-ether linkages of lignin. The process goes
via the quinone methide intermediate or nucleophilic substitution. Generally, less
side-chain cleavage is seen under acid-catalysed rather than alkali-catalysed
reactions. The complete breakdown of the aryl ether linkages leads to the
formation of a reactive resonance-stabilised benzyl carbocation. Under these
conditions condensation reactions occur. The carbocation may form a C-C bond
with an electron-rich carbon atom in the aromatic ring of a lignin fragment or the
protonation of a benzylic oxygen atom may cause inter- or intramolecular
condensation by a SN2 mechanism. The formation of organic acids such as
acetic acid during the delignification process can encourage the formation of the
benzylic carbocation or lead to protonation of a benzylic oxygen atom,
enhancing the SN2 condensation pathway.
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A.2.3.2. Kraft process
The kraft or sulfate process is now the main traditional method for pulping and
hence produces the largest volume of lignin (Smook, 2002). It uses sodium
hydroxide and sodium sulfide under strong alkaline conditions to cleave the ether
bonds in lignin. The delignification process proceeds in three stages. The first
phase occurs around 150°C and is controlled by diffusion. The second stage
occurs between 150°C -170°C, while the final stage occurs at even higher
temperatures. The bulk of the delignification (90 wt%) occurs during the second
stage. The lignin may be recovered from the alkaline liquid remaining after pulp
extraction, the black liquor, by lowering the pH to between 5 and 7.5 with acid
(usually, sulfuric acid) or carbon dioxide (Koljonen et al., 2004). Recent
developments in improving the yield of the kraft process have been reviewed by
Couchene (1998) and Kordsachia et al. (1999) have compared the suitability of
the kraft process for different substrates with the sulfite process.
The kraft process produces lignin with aliphatic thiol groups called kraft lignin.
Kraft lignin is hydrophobic and therefore needs to be modified to improve
reactivity. The high sulfur content (1 wt% - 2 wt%) of kraft lignin is also a
major reason why its main application has been in energy generation in pulp
mills.
The kraft process goes by alkaline hydrolysis in which the β-1,4 links in
cellulose are cleaved, allowing the lignin component of biomass to be extracted.
However, the lignin itself is also susceptible to attack by alkali and except for the
diaryl ether linkages, ethers in lignin readily undergo base-induced hydrolysis
under relatively mild conditions.
In alkaline hydrolysis α-aryl ether bonds are more easily broken than β-aryl ether
bonds, particularly in situations where the substructures contain a free phenolic
hydroxyl group in the para position (Baucher et al., 2003, Sakakibara et al.,
1966). Simple heating of the biomass in water results in substantial cleavage of
the α-ether bonds either through a quinone methide intermediate or through
nucleophilic substitution by a SN2 mechanism (Chakar and Ragauskas, 2004).
In alkaline media intermolecular condensation reactions can occur with
competition between the added nucleophiles and anionic lignin fragments (e.g.,
phenolate anions and carbanions) (Olm and Tisdat, 1979). The extent of
183
condensation will depend on the types of structures initially formed. If a
structure contains good leaving groups at the β-carbon, neighboring group
participation reactions resulting in the cleavage of β-aryl ether linkages will
predominate over condensation reactions (Chakar and Ragauskas, 2004).
A.2.3.3. Soda process
The soda process (which goes by alkaline hydrolysis) was the first chemical
pulping method and was patented in 1845. Soda process led kraft pulping which
now dominates the chemical pulping industry. The soda process is now
becoming the predominant method for the chemical pulping of non-wood
material such as bagasse, wheat straw, hemp, kenaf and sisal. This is mainly due
to the development of both low cost chemical recovery methods and effective
effluent treatment technology. It may also be due to less stringent environmental
legislation for effluent discharge in some countries. The pulping process involves
heating the biomass in a pressurised reactor to 140°C - 170°C in the presence of
13 wt% - 16 wt% alkali (typically sodium hydroxide).
Lignin recovered through extraction with sodium hydroxide is normally referred
to as ‘soda lignin’. Soda lignin from non-wood sources is typically difficult to
recover by filtration or centrifugation because its high carboxylic acid content,
arising from oxidation of aliphatic hydroxy groups, makes it a relatively good
dispersant. Heating is therefore required to encourage coagulation and ensure
filtrable material can be obtained. Soda non-wood lignin recovery has been
patented by Abaecherli et al.(1998). As soda lignin contains no sulfur and little
hemicellulose or oxidised defect structures, it has good potential for use in high
value product.
A.2.3.4. Other fractionation processes
With the push to produce cellulosic ethanol and bio-diesel, additional sources of
lignin will be available through various pre-treatment technologies. Promising
pre-treatment technologies for lignocellulosic biomass involve a combination of
physical, chemical, biochemical and thermal methods. Physical methods include
steam explosion, pulverising and hydrothermolysis (Mosier et al., 2005). The
principal chemical methods are the use of ammonia expansion, aqueous
184
ammonia, dilute and concentrated acids (e.g., H2SO4, HCl, HNO3, H3PO4, SO2)
and alkali (e.g. NaOH, KOH, Ca(OH)2) and ionic liquids. Significantly, all the
approaches under development for production of biofuels from lignocellulosics
are likely to produce lignin with little or no sulfur, increasing the scope for the
manufacture of value-added products.
Organic solvents (e.g. ethanol, formic acid, acetic acid, methanol) produce a
form of lignin, called organosolv lignin. The benefits of organosolv lignin over
sulfonated and kraft lignins include no sulfur, greater ability to be derivatised,
lower ash content, higher purity (due to lower carbohydrate content), generally
lower molecular weight and more hydrophobic (Lora and Glasser, 2002). This
delignification process is not used widely because the pulp produced is of lower
quality than that of soda or kraft process and there is extensive corrosion of the
plant equipment.
A relatively recent development in biomass fractionation is the application of
ionic liquids (IL) to fractionate lignocellulosic materials. Ionic liquids usually
consist of a large asymmetric organic cation and a small anion and typically have
negligible vapour pressure, very low flammability and a wide liquidus
temperature range. Most work on IL as biomass solvents has used
alkylimidazolium IL for dissolving cellulose. The mechanism of dissolution
involves the coordination of small hydrogen acceptors, such as chloride ions, to
the hydroxy groups of cellulose, breaking the strong intramolecular H-bonding
between the cellulose fibres (Spear et al., 2002, Swatloski et al., 2003). An ionic
liquid mixture containing 1-ethyl-3-methylimidazolium cation and a mixture of
alkylbenzenesulfonates with xylenesulfonate as the main anion has been used to
extract lignin from sugarcane bagasse at atmospheric pressure and elevated
temperatures (170°C - 190°C) (Tan et al., 2009). The addition of small amounts
of sodium xylene sulfonate to the ionic liquid mixture aided the cleavage of ether
groups in lignin. This was attributed to the sodium ions coordinating to the ether
oxygen, thereby increasing the carbonium ion character of the ether carbon
atoms and enhancing their susceptibility to nucleophilic attack by the
arylsulfonate groups of the ionic liquid (Tan et al., 2009). Lignins were
recovered from IL by precipitation, allowing the IL to be recycled. Lignins with
molecular weights around 2220 g mol-1 obtained by this process contained
185
between 0.6 wt% and 2 wt% ash and about ~1.5 wt% sulfur. Low levels of
hemicellulose (< 0.1 wt.%) were also detected. Fasching et al.(2007) developed a
new facile method for the isolation of lignin from wood using a mixture of N-
methylimidozole and dimethylsulfoxide. Lignin was isolated by pricipitation
using dioxane/water mixture. Other classes of IL, such as alkylphosphonium IL,
which we are currently investigating, solubilise lignin by similar mechanisms as
those under acidic conditions. These lignins were sulfur-free and were of low
molecular weights.
A.2.4. Phys ica l Proper t ies of L ignin The physicochemical state of lignin dictates how and where it can be utilised in
the manufacture of various products. The source from which lignin is obtained
and the method of extraction has a strong bearing on its properties (Lora and
Glasser, 2002). As a highly cross-linked material with widely varying
functionality, lignin may not readily be characterised to give meaningful
molecular weight data, but other parameters more directly relevant to end-use
properties may be assessed. Despite this, the molecular weight data does provide
some useful guide. Table A.2-1 gives the functional groups and molecular
weight of selected lignins. The reactivities of these lignins will impact on the
attributes of the end products. For example, Muller et al. (1984) found that kraft
lignin-based phenol formaldehyde resins have superior properties to steam
exploded lignin-based phenol formaldehyde resins.
Tab le A.2-1 Molecu la r we ig h t and fun ct iona l g ro ups o f l i gn ins
Lignin type Mn (g mol-1) COOH (%) OH phenolic (%) Methoxy (%)
Soda (bagasse) 2160 13.6 5.1 10.0
Organosolv (bagasse) 2000 7.7 3.4 15.1
Soda (wheat straw) 1700 7.2 2.6 16
Organosolv
(hardwood)
800 3.6 3.7 19
Kraft (softwood) 3000 4.1 2.6 14
186
Another important parameter is the glass transition temperature, Tg, which is an
indirect measure of crystallinity and a degree of cross-linking and directly
indicates the rubbery region of the material (Table A.2-2) (Gargulak and Lebo,
2000).
Tab le A.2-2 Tg o f d i f f e ren t l i gn in t ypes (Ga rgu la k and Lebo, 20 00)
Types of lignin Tg (°C)
Milled wood lignin
-Hardwood
-Softwood
110-130
138-160
Kraft lignin 124-174
Organosolv lignin 91-97
Steam explosion lignin 113-139
Lignin Tg will depend on the amount of water and polysaccharides, as well as
molecular weight and chemical functionalisation, but in general the Tg will be
lower the greater the mobility of the lignin molecules. While Tg generally
increases with increasing molecular weight, the impact of structural variation
based on the degree of polymerisation has only recently been established.
Baumberger and co-workers (2002) showed using a series of transgenic poplars
that the variations in Tg were closely related to the degree of polymerisation of
lignin as determined by thioacidolysis. This is illustrated in Figure A.2-4, where
the Tg increases with the degree of condensation, expressed as the fraction of
phenylpropanoid units involved in C-C linkages.
187
Figure A.2-4 Correlation between the glass transition temperature (Tg) and
the degree of condensation (% phenylpropanoid units involved in C-C linkages) of milled wood and enzyme lignins isolated from control and transgenic poplars (Baumberger et al., 2002). Data for control plants are shown as open symbols, and data for transgenic plants derived from those controls are shown as closed symbols. Figure redrawn with permission from Baumberger et al. (2002)
The reactivity and physicochemical properties of lignins are dependent to certain
extent, on their molecular weight distribution. Recently, Baumberger et al.
(2007) developed the use of size-exclusion chromatography to measure the
molecular weight distribution of lignin.
More potential applications of lignin can be realised if the miscibility of lignin
with other polymeric materials can be improved. This may be done through the
chemical modification of lignin with appropriate hydrophobic groups (e.g.
butyrate, hydroxypropyl, ethyl) (Ghosh et al., 2000, Uraki et al., 1997) or
through the formation of lignin copolymers (Wang et al., 1992). Pouteau and his
coworkers (2004) examined the compatibility of lignin-polymer blends by image
analysis. A correlation (Figure A.2-5) between the solubility parameter of kraft
lignin (20.5-22.5 (MPa)1/2) and the solubility parameters of different polymers
was obtained. The data shown does not discriminate between the molecular
170
175
180
185
190
45 50 55 60 65 70 75 80
Tg
(C
)
% units involved in C-C bonds
(°C
)
188
weight of lignin fractions, but only low molecular weight lignins are compatible
with apolar and very polar matrices.
Figure A.2-5 Correlation between total aggregate surface area observed per photo and the solubility parameter of the polymer matrix (Pouteau et al., 2004). Figure redrawn with permission from Pouteau et al. (2004).
A.2.5. App l icat ions There are many commercial applications of low value where lignins
(predominantly lignosulfonates) are used because of their surface-active
properties (Gargulak and Lebo, 2000, Stewart, 2008). Table A.2-3 gives the
variety of these lignosulfonate products.
Tab le A.2-3 App l i ca t i on o f l i gno su l fon ate p rodu c ts based o n the i r su r fa ce-a c t i v e p rope r t ies
Products Reference
Concrete additives (Sestauber et al., 1988, Shperber et al.,
2004)
0
10000
20000
30000
40000
15 17 19 21 23 25 27
Ave
rag
e s
urf
ace
per p
ho
to
Solubility Parameter (MPa)1/2
189
Animal feed pelleting aid (Winowiski and Zajakowski, 1998)
Metallic ore processing (Clough, 1996)
Oil well drilling muds (Detroit and Sanford, 1989, Kelly, 1983)
Dust control (Buchholz and Quinn, 1994, Fiske, 1992)
Phenol-formaldehyde resins (Raskin et al., 2002)
Lignosulfonates are also used to produce a number of value-added products for
specialty markets (Gargulak and Lebo, 2000). Table A.2-4 gives the variety of
these lignosulfonate products.
Tab le A.2-4 L igno su l fon ate p rod uct s in spec ia l i t y ma rket s
Products Reference
Vanillin (Bjorsvik and Minisci, 1999, Gogotov, 2000)
Pesticides (Lebo, 1996)
Dispersant for carbon black (Goncharov et al., 2001)
Dyes and pigments (Hale and Xu, 1997)
Gypsum board (Northey, 2002)
Water treatments (Jones, 2004, Zhuang and Walsh, 2003)
Scale inhibitors (Ouyang et al., 2006)
Industrial cleaners (Jones, 2008)
Emulsifiers (Gundersen et al., 2001, Sjoblom et al., 2000)
Matrix for micronutrient (Docquier et al., 2007, Meier et al., 1993,
190
fertilisers Niemi et al., 2005)
Wood preservatives (Dumitrescu et al., 2002, Lin and Bushar,
1991)
Battery expanders (Pavlov et al., 2000)
Specialty chelants (Khabarov et al., 2001)
Bricks, refractories and
ceramics
(Pivinskii et al., 2006)
Retention aids in papermaking (Vaughan et al., 1998)
Blending of two or more polymers provides the ability to tailor material
properties to achieve specific goals with higher value. While a particular
homopolymer will have properties that can be tailored by controlling molecular
weight and the degree of branching and crosslinking, blending of polymers
makes a vastly greater range of potential materials properties available. As well
as making simple additive properties accessible, in many instances polymer
blending results in high-performance composite materials as a result of
synergistic interactions between the components. However, many polymer
combinations are immiscible and so exist in two different phases in the polymer
matrix. This separation into phases can result in poor stress transfer between the
phases, thereby lowering the mechanical properties of the blend to that at least of
one of the individual components. When incorporated in blends with natural and
synthetic polymers, lignin generally increases the modulus and cold
crystallisation temperature but decreases the melt temperature. The addition of
plasticisers to such systems have been found to improve the mechanical
properties by reducing the degree of self-association between lignin molecules,
improving lignin-polymer miscibility (Feldman et al., 2001). Because lignin
possesses easily-functionalisable hydroxyl and carboxylic acid groups, its
compatibility with different polymer types has been extensively examined. The
191
following section presents some examples of lignin blends with natural and
synthetic polymers.
Natural polymers are synthesised by living organisms or by enzymes isolated
from living organisms, through sophisticated biosynthetic pathways requiring
carbon dioxide consumption. These ‘environmentally friendly’ polymers include
cellulose, hemicellulose, lignin, starch, proteins, nucleic acids and linear
aliphatic polyesters. The ability to control the hydrophilicity of lignin means that
it could in principle form composite materials with any of these polymers, while
the physicochemical qualities of lignin means that it can in many cases improve
the tensile strength and bulk modulus of these biopolymers, and protect the
composite against oxidative degradation under UV light or elevated temperature.
Feldman (2002) and more recently Stewart (2008) have reviewed lignin blending
with synthetic polymers. The present review will discuss protein-lignin blends,
starch-lignin blends, epoxy-lignin composites and phenol-formaldehyde resins
where all or part of the phenol is derived from lignin, polyolefin-lignin blends,
lignin blends with vinyl polymers, lignin-polyester blends, lignin as a component
of polyurethanes, synthetic rubber-lignin blends, graft copolymers of lignin and
the prospects of lignin incorporation into further polymer systems. Most of these
copolymers and polymer blends are currently in the research phase with the
intent of commercial applications.
A.2.5.1. Protein-lignin blends
Proteins have long been used for the production of plastics and resins (Huang et
al., 2004, Nagele et al., 2000). The main drawbacks of protein-based materials
are high water absorption and the difficulty of separating the proteins from
naturally occurring colourants without denaturation, however these obstacles are
gradually being overcome (John and Bhattacharya, 1999, Otaigbe and Adams,
1997, Zhong and Sun, 2001). As a crosslinked material with a largely aromatic
structure, lignin has the capacity to increase the tensile strength, Young’s
modulus, thermal stability and elongation at break of protein materials.
The addition of soda lignin to soy protein plastics has been shown to reduce
water absorption, as well as improving the mechanical properties of soy
protein/glycerol blends. Blends containing 50 wt% soda lignin have a tensile
192
strength twice that of unblended soy protein (Huang et al., 2003). Thermoplastic
materials comprising lignin and protein blended with natural rubber, have been
patented. These materials have been shown to have improved impact resistance
compared to lignin-free formulations (Nagele et al., 2000).
Hydrogen-bonding interactions are often insufficient to ensure adequate mixing
of lignin with protein. Huang et al. (2004) blended kraft lignin with soy protein
using methylene diphenyl diisocyanate (MDI) as a compatibiliser. MDI will
form urethane links between hydroxy groups on lignin molecules and in the
protein. Only a slight reduction in water absorption was observed, but the
addition of 2 wt% MDI caused a simultaneous enhancement of modulus,
strength, and elongation at break of the polymer blends, which was attributed to
graft copolymerisation and crosslinking (Huang et al., 2004).
An alternative strategy for enhancing the compatibility of lignin with protein,
rather than adding a compatibiliser, is chemical or enzymatic modifications of
the lignin. Blending soy protein with hydroxypropylated soda lignin resulted in a
200 % increase in the tensile strength of the blended material, (Chen et al., 2006,
Wei et al., 2006) without reducing the elongation at break (Huang et al., 2006).
Wei et al. (2006) suggested that improved mechanical properties of protein
blended with hydroxylpropyl lignin molecules were due to: (a) the formation of
supramolecular domains by hydroxylpropyl lignin, (b) the strong adhesion
between the hydroxylpropyl group and soy protein and, (c) the interpenetration
of the soy protein molecules into the supramolecular hydroxylpropyl domain.
Protein has also been incorporated in more complex composite materials, e.g., an
adhesive composition of low molecular weight polyaminopolyamide-
epichlorohydrin resin and protein has been patented (Spraul et al., 2008).
While most processing of gluten protein increases the degree of cross-linking,
incorporation of kraft lignin in gluten reduced protein/protein interactions,
prevented loss of solubility (Kunanopparat et al., 2009). This has obvious
implications for processibility of gluten-based materials, suggesting kraft lignin
is a promising additive for such materials. It was suggested that kraft lignin had a
radical scavenging activity, reacting with the sulfur-centred radicals responsible
for gluten crosslinking.
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A.2.5.2. Starch-lignin blends
The use of starch-based films for packaging materials has increased recently as
they degrade readily in the environment in comparison to conventional synthetic
materials. However, a significant disadvantage of starch films is that they have
very poor water resistance. Blending with hydrophobic polymers can clearly
improve the water resistance of starch, and lignin has a high compatibility with
starch making it an obvious candidate for blending. Baumberger (2002) has
reviewed studies involving starch-lignin films, giving an overview of methods of
preparation, thermomechanical properties, mechanisms of starch-lignin
interactions and potential target applications of starch-lignin blends.
Lepifre et al. (2004) compared the reactivity of films of three soda lignins (one
derived from sugarcane bagasse and the other two from wheat straw) with starch
on exposure to radiation doses of 200 kGy and 400 kGy, using spectroscopic and
chromatographic techniques. Infrared analysis of the bagasse lignin-starch film,
in contrast to the wheat straw lignin, showed evidence of condensation probably
related to the presence of reactive ferulic acid, and that irradiation improved
compatibility of the two polymers.
Lepifre et al. (2004) found that grafting of starch films with lignin gave
significant improvements in water resistance. The higher water resistance of
lignin/starch blends is attributable to the partial compatibility of lignin with the
amylose component of starch, the presence of hydrophobic lignin at the surface
of the material due to surface activity of phenolic groups, and cross-linking
between the starch-rich phase and the lignin-rich phase (Baumberger et al.,
2000). The work by Baumberger et al. (1998) established that reduced water
content and water solubility starch-kraft lignin blends was due to the amount of
water soluble phenolics present in lignin as these hydrophilic compounds are
likely to interact with the starch matrix, through hydrogen bonding, and lead to
increased bonding to lignin. Figure A.2-6 shows the bonding between β-1
stilbene (a component) found in lignin and the amylose portion of starch. The
increase in elongation at break for the starch-kraft lignin blend compared to
starch was attributed to the increased plasticity of the starch matrix due to the
presence of low molecular phenolics and amphiphilic fatty acids.
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Figure A.2-6 Hydrogen bonding between β-1 stilbene and amylose. Composite films of lignin, starch, and cellulose have been cast from ionic liquid
at room temperature, with the product showing good mechanical properties,
thermal stability, and resistance to gas permeation (Wu et al., 2009).
Ke et al. (2003) studied the effect of amylose content on the mechanical
properties and moisture uptake of starch films. Three dry corn starches with
different amylose contents: Amioca (0 wt% amylose ); HylonV (50 wt%
amylose) and HylonVII (70 wt% amylose); were blended with poly(lactic acid)
at various starch/poly lactic acid ratios and characterised for morphology,
mechanical properties and water absorption. It was shown that starch with 50
wt% or more amylose content effectively reduced moisture uptake than those
with the higher percentage amounts of amylopectin. The explanation given was
that although amylopectin is more crystalline than amylose, its large branched
molecules contains ~75 wt% amorphous structure which readily absorb water
(Ke et al., 2003). Moreover no significant difference in mechanical properties
was observed among starches with varying amylose content, except that the
blend containing 50 wt% amylose had slightly greater strength.
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Based on the foregoing, to produce starch-lignin blends with improved properties
research should be directed in the following areas: (a) reducing the
hydrodynamic volume of lignin and increasing its phenolic hydroxyl group
content, (b) attaching hydrophobic groups to both starch and lignin, (c) including
high molecular weight plasticisers such as sorbitol and maltitol (Ghosh et al.,
2000), (d) using starch polymer with a high amylose content and (e) forming
lignin esters prior of blending with starch. The use of plasticisers will minimise
starch degradation and improve processability. The acetylation of the hydroxyl
group in low molecular weight lignin will reduce the amount of hydroxyl groups
available for water molecules to attract to and hence improve the water resistance
of the blends. The attachment of acetyl groups to lignin will reduce hydrogen
bonding increasing the free volume of the amorphous component of starch,
thereby reducing Tg. The miscibility of the starch-lignin blends property
relationships could be studied by Fourier transform infrared (FT-IR)
spectroscopy, Raman spectroscopy and differential scanning calorimetry (DSC)
in order to evaluate molecular interactions between the two components.
A.2.5.3. Polyhydroxyalkanoates
Polyhydroxyalkanoates (PHA) are a group of biodegradable and biocompatible
linear aliphatic polyesters mainly composed of R-(–)-3-hydroxyalkanoate units,
produced as carbon and energy storage materials by a range of algae and
bacteria. PHA have been reported with alkanoates ranging in length from C3 to
C14, but the most common are polyhydroxybutanoate (PHB, C4) and
polyhydroxyvalerate (PHV, C5) and copolymers of C4 and C5 alkanoates
(PHBV) (Reddy et al., 2003).
Unlike most biopolymers, PHA are insoluble in water and have low permeability
towards oxygen, carbon dioxide and water. These barrier properties make PHA
good candidates for the production of packaging products like bottles, bags,
wrapping film and disposable nappies. These applications have not been fully
realised because PHB and PHV are relatively stiff and brittle and are thermally
unstable during processing.
Blending with lignin is one possible strategy for overcoming the mechanical
disadvantages of PHA. Ghosh et al. (2000) investigated the thermoplastic blends
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of several biodegradable polymers with organosolv lignin and organosolv lignin
ester based on both solvent casting and melt processing. Blends of PHB with
lignin are claimed to have a high degree of recyclability (Yao, 2008). On
addition of up to 20 wt% lignin to PHB, improvements were seen in Tg, melting
point, Young’s modulus, and the degree of crystallinity (Ghosh et al., 2000).
The addition of lignin reduced the crystallinity of PHB more than addition of
lignin butyrate, suggesting greater compatibility of PHB with lignin than lignin
butyrate. Recently, Mousavioun et al. (2010) examined the miscibility between
PHB and bagasse soda lignins (having distinct chemical group functionality)
based on the Tg of their blends. A single Tg implies complete compatibility
between the components, while two or more Tg values suggest that the degree of
miscibility is restricted. Figure A.2-7 indicates that with the lignin content <40
wt% there is compatibility between PHB and lignin. The Tg were higher for the
blends obtained from the lignin fraction containing higher xylan and phenolic
hydroxyl content, but lower for higher methoxyl and carboxylic acid content.
This implies that the association between lignin and PHB is probably related to
the chemical functionality of the lignin polymer as the molecular weights of
these lignin fractions are similar, approximately 2400 g mol-1. In fact it was
shown by FT-IR that the miscibility between PHB and soda lignin was due to
hydrogen bond formation between the carbonyl group of PHB and the phenol
hydroxyl group of lignin (Mousavioun et al., 2010).
Blends of lignin butyrate with the slightly more hydrophobic polymer PHBV
gave a significant reduction in crystallinity compared to blends with PHB.
Meister et al. (1993) have reported that grafting lignin with styrene-acrylonitrile
copolymer improves its compatibility with PHB-PHV.
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Figure A.2-7 Miscibility of lignin/PHB blends based on Tg. Lignin Tg,▲; PHB Tg,■.
Camargo et al. (2002) investigated the thermal, mechanical and optical properties
of bagasse lignin blended with PHB, as well as the biodegradation of the blends.
A significant increase in Tg was observed and the PHB/lignin blend was readily
degraded by the common fungi species Trametes versicolor. The significant
increase in Tg obviously related to the interactions between the reactive
functional groups of lignin and the carbonyl groups of PHB. Weihua et al. (2004)
investigated the effect of 1 wt% lignin on the nucleation of PHB by studying the
kinetics of both isothermal and nonisothermal PHB crystallisation. DSC showed
that not only did lignin act as a nucleating agent, decreasing the activation
energy of crystallisation, but it reduced the size of the spherulites to give a less
brittle material.
A.2.5.4. Polylactides and polyglycolides
Poly(L-lactic acid) (PLA) is a crystalline biodegradable polymer which like PHA
has poor processing properties because of its high crystallinity. Copolymers of
L-lactic acid and L-glycolic acid are frequently used in biomedical applications
to enable the tailoring of flexibility and degradation rate. Li et al. (2003)
examined the thermal and mechanical properties of PLA/lignin blends, with
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results indicating a strong intermolecular hydrogen-bonding interaction between
PLA and lignin. The tensile strength and elongation at break decreased with
lignin content, while the Young’s modulus remained almost constant up to a
lignin content of 20 wt%. At a lignin content greater than 20 wt%, thermal
degradation of PLA was enhanced. More recently, ring-opening polymerisation
of cyclic lactides with lignin has been used to create graft-copolymer additives
that can significantly reduce the crystallinity and improve the processing and
end-use performance of PLA (Uyama et al., 2008). Graupner (2008) used lignin
to reinforce PLA/cotton composites and compared the mechanical properties of
the composites with those of PLA/kenaf composites. Addition of lignin
appeared to enhance the adhesion between the cotton fibres and PLA, improving
the tensile strength and Young’s modulus, though the impact resistance
decreased (Graupner, 2008). Lignin has also been added to PLA in order to
reduce its flammability, giving performance competitive with commercial
intumescent formulations (Reti et al., 2008).
From the foregoing, it is evident that not much work has been carried out to
understand the interactions between lignin and these crystalline polymers. The
use of solid state nuclear magnetic resonance (NMR) and relaxation methods
should be included in the analytical tools to study the interactions of lignin and
these interacting polymers in order develop a better understanding of the nature
of the blends for property enhancement.
A.2.5.5. Epoxy resin blends
Substitution of lignin for phenol is a possible route toward the preparation of
inexpensive and renewable epoxy-resin adhesives. In fact, entirely renewable
epoxy-resins have been prepared using lignin and epoxides of plant origin
(Hirose, 2006, Watado et al., 2009). A very wide variety of co-monomers and
curing reagents have been applied to prepare lignin-derived epoxy resins (Ebata,
2004, Hirose et al., 2002).
The effect of lignin blending with epoxy resins is strongly affected by the type of
lignin used (Feldman, 2002). Commercial hardwood lignins have been reported
to improve adhesion to epoxy resins more than Indulin, a softwood lignin, a
result which correlates well with the density of hydrogen-bonding groups in the
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material. Tomlinite (a commercial soda lignin) lignin (20 wt%) gave the highest
adhesive joint shear strength. In general, differences in performance could be
related to the differences in molecular weight and the type and amount of
functional groups (Feldman, 2002). Investigation of the viscoelastic properties
of cured kraft lignin/epoxy resins has been found to have a very broad Tg, which
suggests they may be suitable for application as adhesives or as damping
materials for noise and vibration (Tomita, 1998). Epoxy-resins derived from
lignin have also been applied in concrete formulations (Cheng et al., 2005) and
in a range of fibreboard and plywood products (Okabe et al., 2006).
Feldman et al. (1991a, 1991b) studied a bisphenol A-polyamine hardener-based
epoxy adhesive incorporating kraft lignin. Blends with up to 40 wt% kraft lignin
were cured at room temperature or above their Tg, demonstrated enhanced
bonding between the components. The improvement was attributed to
association between lignin and the unreacted amine groups of the hardener. In
another study, Feldman and Khoury (1988) observed that epoxy blends with 10
wt% and 20 wt% of lignin improved the adhesion tensile strength of an epoxy
polymer system. While blending with 5 wt% to 20 wt% lignin had little effect
on the initial adhesive shear strength or the weatherability of the epoxy-lignin
blend, after post-curing (4 h at 75 ºC) significant improvement of adhesive
strength under shear was observed.
Modifying the lignin structure by ozonisation was found to have little effect on
the properties of epoxy resins prepared from soda lignin and epoxy compounds
(polyethylene glycol diglycidyl ether and bisphenol A diglycidyl ether) which
could be prepared with acceptable shear strengths in applications as wood
adhesive (Nonaka et al., 1996). Only one Tg was observed in resins of this kind,
suggesting formation of interpenetrating polymer networks (Nonaka et al.,
1997). Epoxy resins prepared from lignin, glycerol, and succinic anhydride
which were cured with dimethylbenzylamine at a range of ratios showed a
constant decomposition temperature, regardless of lignin and glycerol content
(Hirose and Hatakeyama, 2006).
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A.2.5.6. Phenol-formaldehyde resins
Extensive work has been carried out with a number of different lignin types as
substitutes for phenol in phenol-formaldehyde resins. These have primarily been
considered for use in adhesive applications, though there has been some
application of lignin-containing phenol-formaldehyde resins as foams (Frollini et
al., 2004). The state of work in this field to 2002 was comprehensively reviewed
by Feldman (2002). The properties of wood adhesive products produced with
lignin-based phenol-formaldehyde resins have been found to be comparable with
those of commercial resins up to 35 wt% partial replacement with lignin
(Kulshreshtha and Vasile, 2002). A range of different lignins, including
organosolv lignin, soda lignin, and lignosulfonates, have been used in phenol-
formaldehyde resin preparation, and black liquor has even been applied directly
(Nada et al., 2003, Wang et al., 2006). A number of methods for lignin
derivatisation for forming phenol-formaldehyde resins are described in the
literature. These phenolysis methods are (a) the lignin reacts with phenol and the
lignin-phenol complex is then reacted with formaldehyde, (b) the lignin which
reacts with phenol and formaldehyde, and the pre-polymer is then reacted with
phenol, (c) phenol reacts with formaldehyde and the mixture is then reacted with
lignin, and (d) the lignin reacts with formaldehyde and the hydroxymethylated
lignin is then reacted with phenol. The phenolation process may be acid or base
catalysed. The condensation reaction occurs between the ortho or para position
of phenol and the side chain of the phenylpropane units of lignin in which the α-
position is substituted by hydroxyl, etherified lignin residue or a double bond-
carbon linked lignin residue. Incorporation of lignin into phenol-formaldehyde
resins has been demonstrated to delay the first glass transition and speed up
curing (Khan and Ashraf, 2006, Khan and Ashraf, 2007).
Vazquez et al. (1999) and Cetin and Ozman (2002), have shown phenol-
formaldehyde resins prepared using organosolv lignin and subsequent plywood
board formation produced board knife-test results better than those obtained with
a commercial phenol-formaldehyde resin. In contrast, Gardner and McGinnis
(1988) prepared lignin-based resins with kraft lignin and steam-exploded
hardwood lignin showing lower reactivity and poorer physical properties than
the pure phenol resin. This variation in results is consistent with other reports
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indicating that the method of extraction and the source from which the lignin is
derived has a strong bearing on the properties of the phenol-formaldehyde resin.
For example, Olivares et al. (1988) reported that different fractions of softwood
lignin separated by ultrafiltration after methylation and demethylation gave
different reactivities toward formaldehyde, leading to different mechanical and
water absorption properties. In another example, Piccolo et al. (1997) showed
that during resol synthesis organosolv bagasse lignin acted as a chain extender.
As a result, molded resins prepared with 40 wt% lignin exhibited modulus
extension at elevated temperatures.
Park et al. (2008) studied the partial substitution of phenol in phenol
formaldehyde resin with high-purity bagasse organosolv lignin. Purification by
extraction with cyclohexane/ethanol removed waxes, lipids, tannins in the lignin
prior to synthesis. The Tg of the resins were between 125 ºC and 150 ºC, and this
transition was clearly evident in the resins when the lignin content was increased
from 10 wt% to 40 wt%. Conversion profiles for lignin/phenol-formaldehyde
resins obtained by differential scanning calorimetry are shown in Figure A.2-8,
demonstrating that partial replacement of phenol with lignin increases the rate of
conversion. The conversion profile is relatively unchanged with the addition of
10 wt% lignin, however, the initial rate of conversion increases markedly upon
increase in lignin concentration to 20 wt% and even further when the
concentration is increased to 30 wt%. Further addition of lignin to 40 wt%
decreases the rate of conversion from the 30 wt% value, but the conversion rate
is still higher than the phenol-formaldehyde resin. In the same study, cardboard
coated with lignin/phenol-formaldehyde showed water resistance properties far
superior to untreated cardboard or cardboard treated with an equivalent phenol-
formaldehyde resin (Park et al., 2008, Pizzi, 2003). Phenol-formaldehyde-type
adhesives prepared from lignosulfonate derived from grasses (bagasse, kaigrass
and wheat straw) have demonstrated acceptable performance qualities at up to 70
wt% lignosulfonate content (Akhtar et al., 2009, Liu et al., 2006). The best
adhesive properties on incorporation into phenol-formaldehyde resins of wheat
straw soda-lignin were found for the lower molecular weight fractions (Liu et al.,
2008).
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Figure A.2-8 Conversion profiles of lignin-based phenol formaldehyde resins (Park et al. 2008)
Peng and Riedl (1994) have shown that the reactivity of lignosulfonate with
formaldehyde is increased when wheat starch was added as a filler, and less
condensation was apparent. Hydroxylmethylation has been reported to produce
resins with improved properties in comparison to unmodified lignin (Yang and
Liu, 2002). It would be interesting to see if the addition of starch to the
hydroxymethylation procedure of lignin described by Muller and Glasser (1984)
would further enhance the reactivity of the hydroxymethylated lignin and
produce resins of improved quality. In another application of multiple natural
products in a composite material, pulverised lignocellulosic materials such as
sisal fibre have been applied as fillers in lignin-based phenolic resin (Frollini et
al., 2004).
From an environmental point of view, an important advantage of using lignin in
partial replacement of phenol-formaldehyde resin is the decrease in
formaldehyde emission during processing (Kulshreshtha and Vasile, 2002). It is
also possible to avoid this volatile and toxic compound entirely, with good
materials properties having been demonstrated for a resin composed of lignin
and the non-volatile aldehyde glyoxal (Mansouri et al., 2007). The overall
0
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90 100 110 120 130 140 150 160
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consensus is that lignin-based resins generally have weaker adhesive properties,
and a high degree of variability in adhesion performance (Cyr and Ritchie,
1989). The presence of plasticisers or contaminants, such as very low molecular
weight lignin, is suspected to be largely responsible for the low bond strengths
obtained, (Hiro-kuni and Kenichi, 1989, Lora, 2002) while the variability is
probably due to the sensitive dependence of properties on the source and history
of the lignin, as mentioned above.
A.2.5.7. Lignin-polyolefin blends
The main objectives of incorporating lignin in polyolefins are to act as a
stabiliser against oxidation under UV radiation or at elevated temperatures, or
conversely, to enable the biodegradation of the material. Early investigations of
polymer blending found good compatibility between hydrophobic lignin and
high density polyethylene (HDPE) with little change in properties, but poor
compatibility with low density polyethylene (LDPE) (Deanin et al., 1978).
Some improvements in the tensile modulus of LDPE were found with greater
than 20 wt% lignin incorporation, but tensile strength was poor. The differences
observed between HDPE and LDPE suggest that molecular architecture may
play as large a role as chemical structure in determining the compatibility of
lignin in blends, as the interactions between lignin and the many short branching
chains of LDPE may be entropically unfavourable.
Blends of up to 70 wt% hydrophilic lignin (lignosulfonates) were similar for
both HDPE and LDPE, with increases in Young’s modulus and a decrease in
elongation at break for both classes of blend, with sugar-rich lignosulfonates
giving the largest increase in modulus (Kubat and Stroemvall, 1983). Scanning
electron microscopy of these blends suggested a morphology of thin
HDPE/LDPE fibres in a lignosulfonate matrix.
Straw lignin obtained by steam-explosion has been blended with LDPE, HDPE,
and linear low density polyethylene (LLDPE), giving blends that are stabilised
against UV radiation and can be processed by conventional thermoplastic
methods. While modulus was slightly increased in the blends, tensile strength
and elongation at break were impaired (Pucciariello et al., 2004). Significant
improvements have been observed in the thermal oxidative stability of PE
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blended with lignosulfonate, and incorporation of lignosulfonate also had a
significant impact on the rheology of the polymer melt (Levon et al., 1987).
Ammonium lignosulfonate and epoxy-modified lignosulfonate can act as
nucleating agents in PP processing as well as plasticisers and controllers of melt
flow (Darie et al., 2007). Košíková et al. (1993) investigated sulfur-free lignins
as composites of PP films. PP films containing 2 wt% - 10 wt% of spruce
organosolv lignin and/or beech wood prehydrolysis lignin showed good
compatibility between lignin and PP and sufficient tensile strength. The films
acted as good UV absorbers (Kosikova and Demianova, 1992). The influence of
lignin on the oxidative stability of PP has been examined by Gregorova et al.
(2005) by differential scanning calorimetry under non-isothermal conditions. It
was found that lignin exerts a stabilising effect in both virgin and recycled PP,
with a protection factor increasing with lignin content in the PP matrix, though
the increases with small quantities of lignin were less significant than for PE
(Chodak et al., 1986). Surface modification of lignin/PP blends by treatment
with silicon tetrachloride plasma increased tensile and impact strength by
introducing surface cross-linking (Toriz et al., 2002).
Alexy et al. (2000) used lignin as a filler for both LDPE and PP at concentrations
up to 30 wt%, with only small impacts on tensile strength and melt flow index,
but improvements in processing stability and modulus. Resistance to light and
heat degradation was improved for both PE-lignin and PP-lignin blends. Kraft
lignins acylated with long hydrophobic substituents have been used to
compatibilise fractions of different polyolefins in recycled household waste,
giving good values of tensile strength and elongation at break for blends of
LDPE and PP (Tinnemans and Greidanus, 1984). Compatibility of lignin and
hydroxypropyl lignin with PE is low in comparison with more polar monomers,
making them relatively ineffective in improving bulk modulus (Ciemniecki and
Glasser, 1989, Glasser et al., 1988). The compatibility between lignin and PE/PP
can be improved by grafting ethylene/propylene monomers onto lignin prior to
blending to the polyolefin (Casenave et al., 1996). The Young’s modulus of the
lignin-grafted material prepared by Casenave (1996), Ait-Kadi and Riedl was
similar to that of pure PE at up to 64 wt% lignin content. Chemical modification
of soda lignin with stearoyl chloride has also been effective in increasing its
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compatibility with LDPE, giving significant mixing attested to by improvements
in mechanical properties (Vasile et al., 2006).
Organosolv lignin blends based on the compatilisation of PE with ethylene-vinyl
acetate copolymer (EVA) have been investigated by Alexy et al. (2004). The
addition of 10 wt% EVA gave an approximate 200 wt% increase in tensile
strength and a 1300 wt% increase in elongation at break in comparison to blends
without EVA. A composite material prepared containing 33.6 wt% lignin
displayed acceptable processing and mechanical properties, and was used
successfully in preparing blown films. The compatibility of lignin and EVA was
found to increase with increasing content of vinyl acetate for both soda lignin
and hydroxypropyl lignin (Glasser et al., 1988). Tensile properties were inferior
with less than 10 wt% vinyl acetate and the best tensile properties were obtained
with materials containing between 5 wt% and 20 wt% hydroxypropyl lignin and
greater than 25 wt% vinyl acetate. Ciemniecki and Glasser (1989) also observed
that blends of EVA and hydrodxyropyl lignin showed superior strength
properties as the proportion of the polar vinyl acetate component increased.
In another application of EVA, lignin was added to an EVA/LDPE blend to form
a homogeneous blend exhibiting a single glass transition temperature that could
be used to prepare a foam (Zhou and Luo, 2007). LDPE grafted with maleic
anhydride is another compatabiliser that has been successfully used to mix LDPE
and lignin, with scanning electron microscopy indicating more dispersed lignin
in smaller domains in the presence of maleated LDPE, decreasing the melting
temperature and improving stability to thermal oxidation (Li and Luo, 2005). At
25 wt% loading of lignin and 10 wt% maleated LDPE, blown films could be
prepared with excellent properties.
Processes for preparing degradable plastic blends of ethylene copolymers and
organosolv lignin have been patented by Bono (1994). Lignin was incorporated
in the form of powder having a grain diameter of about 1 µm - 5 µm, and
homogeneous films with a thickness of about 15 µm - 25 µm were obtained
showing improved degradation with photoactive and oxidizing agents. The
ability of the lignin-degrading microorganism Phanerochaete chrysosporium to
degrade lignin-PE blends has been reported by Košíková et al. (2001). The
isolation of oligomer fraction from biodegraded polymer blends indicated that
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the biotransformation of lignin during the cultivation process was accompanied
with degradation of the PE matrix.
A.2.5.8. Lignin-vinyl polymer blends
As with polyolefins, vinyl lignin polymers have attracted interest primarily as a
UV and thermal stabiliser. In general, unmodified lignin has poor compatibility
with non-polar vinyl polymers; while the modulus of these blends is increased,
reductions in tensile strength and elongation at break are obtained. Early work
found good compatibility between hydrophobic lignin and relatively polar
poly(vinyl chloride) (PVC), but poor compatibility with polystyrene (Deanin et
al., 1978). However, the source of the lignin can have a considerable impact on
miscibility, and steam-explosion lignin powder has more recently been
successfully blended with atactic polystyrene into a readily processible material
(Pucciariello et al., 2004). Improved blending of polystyrene and lignin has also
been achieved using a copolymer of styrene and vinyl phenol (Henry and
Dadmun, 2009) or cellulose phthalate (Hechenleitner et al., 1997) as
compatibilising agents. In the latter case, a strong dependence of thermal
stability on the hydrophobicity of the lignin used was observed, with the more
hydrophobic lignin fraction promoting stability and the more hydrophilic fraction
reducing stability.
A significant body of research has been carried out on the blending of lignin and
PVC (Banu et al., 2006, El Raghi et al., 2000, Feldman and Banu, 2003, Mishra
et al., 2007). One rationale for this has been to increase the resistance of PVC-
based floor coverings to attack by fungi that can degrade phthalate-based
plasticisers to generate potentially toxic products (Feldman et al., 2003).
Generally homogeneous PVC/lignin blends can be prepared at low lignin
content, with increased rigidity due to the lignin component improving impact
resistance and scratch hardness while reducing flexibility (Mishra et al., 2007).
Larger quantities of lignin with concomitant changes in properties towards
rigidity can be achieved by using plasticisers that can disrupt intermolecular
hydrogen bonding in lignin, (Feldman and Banu, 2003) and in general lignin
may have either an antiplasticising or plasticising effect depending on its
molecular weight and how it is dispersed through the PVC matrix (Banu et al.,
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2006, Feldman et al., 2003). There are reports that thermal stability of PVC can
be improved by the addition of lignin (Szalay and Johnson, 1969). Conversely, a
negative impact of lignin on the stability of PVC to weathering has been
attributed to degradation of lignin under PVC processing conditions (Feldman
and Banu, 1997b). There is some evidence that softwood lignins, generally
having a higher proportion of crosslinked phenol groups, are more effective in
promoting properties of PVC/lignin blends than hardwood lignins (Feldman and
Banu, 1997a).
Polymer blends of hydroxypropyl lignin with poly(methyl methacrylate)
(PMMA), and poly(vinyl alcohol) (PVA) were investigated by Ciemniecki and
Glasser (1989). In both cases compatibility was high, with the lignin being able
to contribute to modulus, while depending on molecular weight the effect of
lignin incorporation could be either plasticising or antiplasticising. In all cases
two-phase materials were produced, but Tg values nevertheless suggest a high
degree of compatibilisation. Blends prepared using injection moulding showed
generally better properties than blends formed by solution casting from organic
solvent (Ciemniecki and Glasser, 1988).
Li et al. (1997) reported a blend of 85 wt% underivatised kraft lignin and
poly(vinyl acetate), prepared with indene and diethyleneglycol benzoate as
plasticisers, which exhibited promising mechanical properties. The modulus and
tensile strength of these blends was strongly influenced by the degree of
association between the lignin molecules. Lignins dissociated by prolonged
incubation in 0.10 M NaOH gave much poorer mechanical properties in the
blends, while lignins associated by incubation in 0.40 M NaOH with a high ionic
strength gave blends with excellent mechanical properties. This work has
significant implications for the entire field of lignin-polymer blends, implying
that the effect of the blended copolymer on non-covalent interactions between
lignin molecules could play a critical role in the properties of blended materials
(Chen and Sarkanen, 2006).
Blends of hydrophobic lignin with water-swellable alternating copolymers of
maleic anhydride have attracted interest as matrices for delivery of agricultural
actives. Acylated kraft lignin was blended with poly(maleic anhydride-alt-
styrene) by solvent casting to give brittle films which could be swollen to up to
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50 times their dry weight in water or dilute aqueous ammonia (Tinnemans and
Greidanus, 1984).
There has been interest in blends of lignin with hydrophilic polymers such as
poly(vinyl alcohol) (PVA) and poly(ethylene oxide) for application in carbon
fibre synthesis (Kubo et al., 2005, Kubo and Kadla, 2004, Kubo and Kadla,
2005). While kraft or organosolv lignins can be spun into fibres, they produce
carbon fibres that are brittle and difficult to handle, and morphological properties
can be significantly improved using miscible (e.g., PEO) or immiscible (e.g.,
PVA) blends of hydrophilic polymer with lignin (Kubo et al., 2005).
Incorporation of lignin in PVA greatly reduces the crystallinity of the PVA and
reduces Tg, suggesting there are strong hydrogen-bonding interactions between
lignin and PVA despite the fact the these blends remain two-phase systems
(Kubo and Kadla, 2003).
A ‘polyionic complex’ of lignosulfonic acid and poly(vinyl pyridine) can be cast
into a thin film and shows good adhesive properties (Hasegawa et al., 2008).
As with polyolefin/lignin blends, blends of lignin with vinyl polymers have been
shown to be biodegradable, with poly(methyl methacrylate) (PMMA) and
polystyrene blends with as little as 10 wt% lignin degrading under the action of a
number of ‘white rot’ fungus species (Milstein et al., 1996). Conversely, lignin
blending with poly(vinyl alcohol) had little effect on its rate of bidegradation
(Pseja et al., 2006). Incorporation of small amounts of lignin has also been
demonstrated to accelerate the thermal depolymerisation of polystyrene and
PMMA (Mansour, 1992).
A.2.5.9. Lignin-polyester blends
Blends of lignin have been prepared with a wide variety of synthetic polyesters,
in addition to the poly(hydroxy alkanoates) and polylactides/polyglycolides
already discussed. These include poly(ethylene terephthalate) (PET), (Agafitei
et al., 1999) poly(butylene terephthalate), (Xu et al., 2007) poly(trimethylene
succinate) (Li and Sarkanen, 2005) and poly(ε-caprolactone) (Nitz et al., 2001a).
Blending of poly(butylene adipate) and poly(trimethylene succinate) with
acylated, methylated and ethylated kraft lignin is most effective when the lignin
has a broad molecular weight distribution (Li and Sarkanen, 2005). These
209
polyesters appear to be relatively less effective plasticisers of lignin than PEG.
On the other hand, alkylated lignin in combination with aliphatic polyester
plasticisers has produced materials with tensile properties very similar to
polystyrene (Sarkanen and Li, 1999).
Blends of methylated and ethylate kraft lignins with aliphatic polyesters appear
to be a potentially versatile class of thermoplastics, with homogeneous blends
obtained when the ratio of methylene/carboxylate ester in the polyester is
between 2 and 4 (Li and Sarkanen, 2003). As with kraft lignin/poly(vinyl
acetate) blends, the association of the lignin molecules into supramolecular
structures is postulated to be largely responsible for the properties of these
blends (Li et al., 1997). The amount of alkylated kraft lignin necessary to disrupt
crystalline domains of the polyester is least when the ratio of
methylene/carboxylate ester in the polyester is between 2.5 and 3.0 (Li and
Sarkanen, 2002).
Lignin can form homogeneous blends with poly(butylene terephthalate) (Xu et
al., 2007) and PET (Kadla and Kubo, 2004). Soda lignin decreases the melting
temperature and Tg of PET, improving its processability, and accelerates
crystallisation implying it can play a role in PET nucleation (Chaudhari et al.,
2006). The compatibility of lignin epoxy-modified with epichlorohydrin with
PET and a poly(ethylene terephthalate/isophthalate) copolymer was studied by
Agafitei et al. (1999). Optimum compatibility with significant increases in
surface and bulk electrical resistivity, reductions in crystallisation temperature,
and increases in melting temperature, were achieved using 4 wt% -10 wt% lignin
(Agafitei et al., 1999).
Organosolv lignin alkylated with propyl, butyl, or pentyl groups formed
homogeneous blends with poly(ε-caprolactone) (PCL), with crystallisation
studies suggesting the miscibility improved as the length of the alkyl chain
increased. Good elongation at break values were obtained even in blends with 50
wt% alkylated lignin (Teramoto et al., 2009). Unmodified straw lignin strongly
stabilised PCL against UV radiation and increased the blend modulus, but
decreased the observed elongation at break, and the two components of the blend
were shown to be immiscible by dynamic mechanical analysis (Pucciariello et
al., 2008). Compatibilisation of PCL with lignin and wood flour could be
210
achieved by incorporation of PCL grafted with maleic anhydride, giving a blend
with a five-fold improvement in modulus and 100 wt% improvement in yield
stress (Nitz et al., 2001a). Lignin was found to retard the rate of decomposition
of these biodegradable composites (Nitz et al., 2001a).
Sulfur-free lignin compounded with poly(butylene-co-adipate-co-terephthalate)
gave improved mechanical properties, but marked differences were seen between
lignin obtained by alkaline pulping of fibre plants such as sisal and abaca and
alkaline pulping of wood, with the lignin derived from the fibre plants giving
superior modulus and yield stress (Nitz et al., 2001b). The blends obtained were
heterogeneous, with the disperse lignin phase occurring in larger domains when
wood lignin was used.
A.2.5.10. Lignin-containing polyurethanes and lignin-polyurethane
blends
The incorporation of lignin and lignin derivatives into polyurethanes has been
investigated in order to (a) increase crosslinking of the polyurethane networks,
(b) increase Tg, (c) increase tensile strength, (d) increase curing rates and, (e)
increase thermal stability (Hatakeyama and Hatakeyama, 2005, Saraf and
Glasser, 1984).
Extensive work has been undertaken on the development and characterisation of
polyurethanes from lignin grafted with polycaprolactone, which gave two-phase
systems with properties controlled by the degree of association of the PCL
chains (Hatakeyama et al., 1998, Hatakeyama et al., 2001a, Hatakeyama et al.,
2001b). Lignin extended with polyethylene oxide has also been used as a basis
for producing polyurethanes, notably in interpenetrating network systems with
PMMA (Kelley et al., 1989, Kelley et al., 1990). Liu et al. (2002) used
propylene oxide-modified lignin with ethylene glycol and methylene
diisocyanate to prepare polyurethane resins potentially suitable for use in hard
foams, with lignin content of 30 wt% or less. One intriguing application as a
geoengineering material is in situ polyurethane/inorganic composites generated
by injecting lignin and isocyanates into sand (Hatakeyama et al., 2005).
Polyurethane/lignin blends have also been investigated. The morphology of such
blends has been studied by Feldman and Lacasse (1989) While SEM revealed an
211
even distribution of lignin particles in the polyurethane matrix, the different
morphologies of the constituent phases could clearly be observed, with
differential scanning calorimetry (DSC) confirming immiscibility. Polyurethane
lignin blends have also been obtained by treating steam explosion lignin from
straw with a range of isocyanates. The presence of ethylene glycol reduced the
yields, and the best results were obtained using an isocyanate terminated
poly(butylene terephthalate) (Bonini and D'Auria, 2007). Ciobanu et al. (2004)
used a polyurethane elastomer blended with flax soda lignin to form
homogeneous solvent-cast films containing between 4.2 wt% and 23.2 wt%
lignin. While the thermal degradation ranges of unmodified polyurethane and the
blends were similar, the presence of lignin accelerated decomposition at lower
temperatures. The tensile strength increased up to 370 wt%, toughness up to 470
wt% and elongation at break up to 160 wt%, for the blends compared to the
unmodified polyurethane film.
A.2.5.11. Rubber-lignin blends
Lignin has attracted most attention as a filler in natural and synthetic rubbers -
that is, as a component of a multiphase mixture, not in a homogeneous blend. It
has been applied as a filler in butadiene-styrene-butadiene and isoprene-styrene-
butadiene rubbers for shoe soles, (Savel'eva et al., 1983) in styrene-butadiene
elastomer, (Kosikova et al., 2003, Kramarova et al., 2007) and in natural rubber
(Kramarova et al., 2007). Soda lignin and calcium lignosulfonate were compared
as fillers in natural rubber, and though neither had properties entirely comparable
to carbon black, soda lignin had better filler properties than calcium
lignosulfonate and showed potential as a low-cost substitute for carbon black
(Lazic et al., 1986). Low molecular weight lignins have been shown to be more
effective in improving the tensile strength of natural rubber than of styrene-
butadiene rubber, being significantly more effective than starch or protein as a
filler for natural rubber but not for styrene-butadiene rubber (Kramarova et al.,
2007).
Lignin-based phenol-formaldehyde resin has demonstrated good mechanical
properties, oil resistance, and resistance to environmental oxidation when used as
a filler in nitrile rubber (Wang et al., 1992).
212
Lignin has also been applied in combination with an oligomeric polyester as a
modifier of isoprene rubber and methylstyrene-butadiene rubber (Savel'eva et al.,
1988). The vulcanisation rate of the rubbers increased and optimum
vulcanisation time decreased, and improvements were obtained in the
mechanical properties suitable for applications as tyre rubber (fatigue strength,
adhesion to reinforcing cord). Improved adhesion to textiles in blends with lignin
has also been observed in blends of lignosulfate with natural rubber (Piaskiewicz
et al., 1998) and styrene-butadiene rubber (Lora et al., 1991). While in these
applications lignin incorporation increases the adhesiveness of the material, a
hydrophobically modified lignin has been applied to pre-vulcanised natural
rubber latex in order to decrease the stickiness of natural rubber latex as a
paperboard coating material (Wang et al., 2008).
A.2.5.12. Lignin-graft-copolymers
Apart from the uses of lignin as a filler in thermoplastics and as a copolymer in
thermosetting polymers, there is the potential for lignin to be used in free-radical
copolymerisation with unsaturated polymers. This potential is limited by the
ability of the phenolic hydroxyl groups in lignin to act as radical scavengers,
initiating the formation of quinonic structures (Barclay et al., 1997, Lu et al.,
1998).
The residual double bonds in lignin are 1,2-disubstituted and hence not reactive
towards free-radical attack, but lignin has a high concentration of benzylic sites
that should be susceptible to hydrogen abstraction and hence afford grafting sites
(Figure A.2-9). The chief limitation on achieving grafted copolymers based on
free-radical monomers and lignin is hence not normally the intrinsic reactivity of
the ligand, but that the high polarity of the hydroxyl groups leads to a molecule
insoluble in non-polar comonomers such as styrene and methyl methacrylate.
213
(a)
(b)
Figure A.2-9 Potential sites for hydrogen abstraction for free-radical grafting from lignin ; (a) benzylic hydrogen, (b) allylic hydrogen from double bond from dehydrozylation
Lignin has been shown to retard the polymerisation of styrene and methyl
methacrylate, (Rizk et al., 1984) but good yields of PMMA-grafted lignin have
been prepared, (Meister and Zhao, 1992) and successful grafting using
conventional radical initiation has also been achieved with acrylamide, (Ibrahim
et al., 2006, Meister et al., 1991) vinyl acetate, (Corti et al., 2003) cationic vinyl
monomers, (Meister and Li, 1990) acrylic acid, (Maelkki et al., 2002),
acrylonitrile (Chen et al., 1996) and sodium acrylate (Potapov et al., 1990).
Interest in grafting polyelectrolytes to lignin arises from the possibility of
incorporating the thermal and mechanical resistance of lignin into polyelectrolyte
applications for extreme environments, such as additives for drilling muds
(Ibrahim et al., 2006). Chemical grafting of PMMA or polystyrene to lignin
produces surface-active materials which have possible applications as wood
coatings (Chen et al., 1995, Gardner et al., 1993). Contact angle on wood
surfaces coated with lignin-PMMA graft copolymer, a measure of
OCH3
O
OH
OCH3
OH
H
OCH3
O
OH
OCH3
OH
-H
O
OCH3
OCH3
OH
H
O
OCH3
OCH3
OH-H
214
hydrophobicity, increased with lignin content, and copolymers of relatively low
molecular weight gave larger contact angles than copolymers of low molecular
weight (Gardner et al., 1993). Sailaja (2005) has reported that lignin grafted with
PMMA using manganese pyrophosphate initiator gave much improved
mechanical properties in blends at up to 50 wt% with PE, in comparison to
blends of PE with unmodified lignin.
A promising means for producing graft copolymers of lignin and free-radical
monomers appears to be initial derivatisation of lignin with more readily
polymerisable moieties, e.g., with isocyanatomethacrylate to give pendant
methacrylate groups readily polymerisable with methyl methacrylate or styrene,
(Glasser and Wang, 1989) or with chloromethylstyrene and methacryloyl
chloride (Da Cunha et al., 1993). Feldman et al. (1991c) carried out free-radical
grafting of maleic anhydride onto lignin in order to facilitate incorporation of the
modified lignin into a polyurethane. They reported both free-radical grafting to
the lignin backbone and a degree of esterification of the phenol hydroxy groups
on treatment with maleic anhydride and a persulfate radical source.
Grafting of methyl methacrylate to lignin using radiation was first reported by
Koshijima and Muraki (1964). Alkoxylation of the phenol groups improved the
effectiveness of radiation grafting, and radiation-curable coatings have been
produced using acrylic acid and propoxylated lignin (Reich et al., 1996).
Radiation-induced grafting of styrene to lignin was facilitated in the presence of
an organic solvent, with better efficiency as the proportion of methanol in the
reactants was increased (Phillips et al., 1972). Increasing moisture content in
wood was correlated with increasing radiation-induced grafting of PMMA to
lignin, presumably a phenomenon related to monomer diffusion within the
matrix (Sutyagina et al., 1987).
Grafting to lignin has also been accomplished through anionic and cationic chain
polymerisation, and chemical (De Oliveira and Glasser, 1994a) or enzymatic
(Huttermann et al., 2000) grafting of complete polymer chains. Oliveira and
Glasser prepared star-like graft copolymers of lignin and poly(caprolactone)
using anionic polymerisation (De Oliveira and Glasser, 1994b) and
heterogeneous composites of these copolymers with poly(vinyl chloride) (De
Oliveira and Glasser, 1994c). While these lignin-PCL copolymers were brittle
215
and had poor mechanical strength on their own (De Oliveira and Glasser, 1990),
they were found to exhibit good plasticisation properties with PVC. Anionic
polymerisation has been used to graft well-characterised polystyrene chains onto
mesylated lignin, producing copolymers suitable for use as compatibilisers for
blends of kraft lignin and polystyrene (Narayan et al., 1989).
Another route to lignin-PCL graft copolymers is by enzymatic polymerisation of
ε–caprolactone (Enoki and Aida, 2007). A similar chemo-enzymatic
polymerisation pathway has also been reported as a means of grafting acrylamide
(Mai et al., 2000a) and acrylic acid (Mai et al., 2001) onto lignin, in a process
where the role of the laccase enzyme appears to be primarily to catalyse the
production of peroxide-derived radicals (Mai et al., 2002). Although grafting of
acrylic acid to calcium lignosulfonates could be successfully carried out with a
hydroperoxide initiator alone, the process was much more effective when the
initiator was used in combination with laccase (Mai et al., 2000b).
A.2.6. Conc lus ions Lignin is a very abundant naturally occurring polymer with good properties for
the applications, of many materials which can play a role in replacing or partly
replacing petroleum-based components in a broad range of composite materials.
Lignin can be isolated in fractions of varying molecular weight and may readily
be functionalised to play a role in a broad range of composite materials. In
addition, lignin can serve as a feedstock for the production of both liquid fuel
and a broad range of commodity chemicals. The importance of lignin in these
applications is likely to increase, as society becomes less tolerant of product
streams that dispose of lignin by landfill or burning and as the exploitation of
lignocellulosic sources for biofuels increase the amount of lignin generated.
Widespread exploitation of these lignocellulosic sources would also dramatically
change the nature of the lignin isolated: today most lignin is hydrophilic sulfated
material produced as a by-product of the pulp and paper industry, but the
thermal, chemical, and biological methods employed in digesting lignocellulosic
material are all likely to give rise to unfunctionalised lignin. For many
applications, this material will be processed in order to improve its quality and
hence lead to the emergence of a viable lignocellulosic biofuels industry. Lignin
of superior quality will afford a significant opportunity to apply it to a much
216
greater extent in polymer composites, controlled-release formulations, and as a
feedstock for fuels and commodity chemicals. Conversely, the development of
these applications on a commercially viable scale will exert a ‘pull’ effect on
lignocellulosic biofuel development, making the industry economically viable at
an earlier stage of fossil fuel resource depletion. Despite hundreds of years of
experience in the pulping of biomass, technically feasible processes for
separation of biomass into its main components still lie mostly below the
threshold of economic viability. The present treatment strategies, whether
thermal, thermochemical or thermomechanical, still require considerably energy
input. Thus an important future research direction is the cost-effective
fractionation of lignocellulosic biomass. Specifically, the processes involved in
lignin recovery from black liquor (such as acid precipitation and membrane
filtration) need to be improved so that better separation, decreased losses during
washing of the precipitated lignin, and improved purity can be achieved.
Research into the use of flocculants, surfactants and ions for effective lignin
isolation from black liquor produced from various fractionation strategies would
also be worthwhile.
217
A.2.7. References Abacherli, A., 1998. Method for precipitation of aromatic polymers from
alkaline wastewater from pulping. WO 9842912. Abdullah, H., Mediaswanti, K.A., Wu, H., 2010. Biochar as a Fuel 2. Significant
differences in fuel quality and ash properties of biochars from various biomass components of Mallee trees. Energy Fuels 24, 1972.
Abreu, H.D.S., Freire, M.D.F.I., 1995. Methoxyl content determination of lignins by 1H NMR. Anais da Academia Brasileira de Ciencias 67, 379-382.
Agafitei, G.E., Pascu, M.C., Cazacu, G., Stoleriu, A., Popa, N., Hogea, R., Vasile, C., 1999. Polyester/lignosulfonate blends with enhanced properties. Angew. Makromol. Chem. 267, 44.
Akhtar, T., Lutfullah, G., Nazli, R., 2009. Synthesis of lignin based phenolic resin and its utilization in the exterior grade plywood. J. Chem. Soc. Pak. 31, 304.
Akin, D.E., Benner, R., 1988. Degradation of polysaccharides and lignin by ruminal bacteria and fungi. Applied and Environmental Microbiology 54, 1117-25.
Alen, R., 2000. Basic chemistry of wood delignification. Papermaking Sci. Technol. 3, 58.
Alexy, P., Kosikova, B., Crkonova, G., Gregorova, A., Martis, P., 2004. Modification of lignin-polyethylene blends with high lignin content using ethylene-vinyl acetate copolymer as modifier. J. Appl. Polym. Sci. 94, 1855.
Alexy, P., Kosíková, B., Podstránska, G., 2000. The effect of blending lignin with polyethylene and polypropylene on physical properties. Polymer 41, 4901-4908.
An, Y., Dong, L., Xing, P., Zhuang, Y., Mo, Z., Feng, Z., 1997. Crystallization kinetics and morphology of poly(β-hydroxybutyrate) and poly(vinyl acetate) blends. Eur. Polym. J. 33, 1449-1452.
Antal, M.J., Varhegyi, G., 1995. Cellulose pyrolysis kinetics – the current state knowledge. Ind. Eng. Chem. Res. 34, 3271.
Antunes, M.C.M., Felisberti, M.I., 2005. Blends of poly(hydroxybutyrate) and poly(ε-caprolactone) obtained from melting mixture. Polym. Sci. Technol. 15, 134-138.
Aoyagi, Y., Yamashita, K., Doi, Y., 2002. Thermal degradation of poly[(R)-3-hydroxybutyrate], poly[ε-caprolactone], and poly[(S)-lactide]. Polym. Degrad. Stab. 76, 53-59.
Aranguren, M.I., Mora, E., DeGroot, J.V., Macosko, C.W., 1992. Effect of reinforcing fillers on the rheology of polymer melts. J. Rheol. 36, 1165.
Avella, M., Rota, G.L., Martuscelli, E., Raimo, M., Sadocco, P., Elegir, G., Riva, R., 2000. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and wheat straw fibre composites: thermal, mechanical properties and biodegradation behaviour. J. Mater. Sci. 35, 829-836.
Banu, D., El-Aghoury, A., Feldman, D., 2006. Contributions to characterization of polyvinyl chloride-lignin blends. J. Appl. Polym. Sci. 101, 2732.
Barclay, L.R.C., Xi, F., Norris, J.Q., 1997. Antioxidant properties of phenolic lignin model compounds. J. Wood Chem. Technol. 17, 73.
218
Barham, P.J., Keller, A., 1986. The relationship between microstructure and mode of fracture in polyhydroxybutyrate. J. Polym. Sci. Part B: Polym. Phys. 24, 69-77.
Barham, P.J., Keller, A., Otun, E.L., Holmes, P.A., 1984. Crystallization and morphology of a bacterial thermoplastic: poly-3-hydroxybutyrate J. Mater. Sci. - Mater. Med. 19(9), 2781-2794.
Barsbay, M., Güner, A., 2007. Miscibility of dextran and poly(ethylene glycol) in solid state: Effect of the solvent choice. Carbohyd. Polym. 69, 214-223.
Baucher, M., Halpin, C., Petit-Conil, M., B., W., 2003. Lignin: genetic engineering and impact on pulping. Crit. Rev. Biochem. Mol. Biol. 38, 305-350.
Baumberger, S., 2002. Starch-lignin films. Chem. Modif., Prop., Usage Lignin 1.
Baumberger, S., Abaecherli, A., Fasching, M., Gellerstedt, G., Gosselink, R., Hortling, B., Li, J., Saake, B., de Jong, E., 2007. Molar mass determination of lignins by size-exclusion chromatography: towards standardisation of the method. Holzforschung 61, 459-468.
Baumberger, S., Dole, P., Lapierre, C., 2002. Using transgenic poplars to elucidate the relationship between the structure and the thermal properties of lignins. J. Agric. Food Chem. 50, 2450.
Baumberger, S., Lapierre, C., Monties, B., 1998. Utilization of pine kraft lignin in starch composites: impact of structural heterogeneity. J. Agric. Food Chem. 46, 2234.
Baumberger, S., Michon, C., Cuvelier, G., Lapierre, C.,2000. Lignin utilization in starch thermoplastics: towards molecular origin of polymer compatability. In: Sixth European workshop on Lignocellulosics and Pulps, pp. 121.
Baurhoo, B., Ruiz-Feria, C.A., Zhao, X., 2008. Purified lignin: Nutritional and health impacts on farm animals--A review. Animal Feed Science and Technology 144, 175-184.
Beamson, G., Briggs, D., 1992. High resolution XPS of organic polymers, Wiley, Chichester.
Bettiga, M., Bengtsson, O., Hahn-Hägerdal, B., Gorwa-Grauslund, M.F., 2009. Arabinose and xylose fermentation by recombinant saccharomyces cerevisiae expressing a fungal pentose utilization pathway. Microb. Cell Fact. 8, No pp given.
Biagini, E., Barontini, F., Tognotti, L., 2006. Devolatilization of biomass fuels and biomass components studied by TG/FTIR technique. Ind. Eng. Chem. Res. 45, 4486.
Bibla, A.K., Ouensanga, A., 1996. Fourier transform infrared spectroscopy study of thermal degradation of sugar cane bagasse. J. Anal. Appl. Pyrol. 38, 61.
Bittencourt, P.R.S., dos Santos, G.L., Gómez Pineda, E.A., Winkler Hechenleitner, A.A., 2005. Studies on the thermal stability and film irradiation effect of poly(vinylalcohol)/kraft lignin blends. J. Ther. Anal. and Calori. 79, 371-374.
Bjorsvik, H.R., Minisci, F., 1999. Fine chemicals from lignosulfonates. 1. synthesis of vanillin by oxidation of lignosulfonates. Org. Process Res. Dev. 3, 330.
219
Blasi, C.D., Branca, C., D’Errico, G., 2000. Degradation characteristics of straw and washed straw. Thermochim. Acta 364, 132.
Boerjan, W., Ralph, J., Baucher, M., 2003. Lignin biosynthesis. Ann. Rev. Plant Biol. 54, 519-549.
Bomben, K.D., Moulder, J.F., Sobol, P.E., Stickle, W.F., 1992. Handbook of X-ray Photoelectron Spectroscopy, Perkin-Elmer, Eden Prairite.
Bonini, C., D'Auria, M., 2007. New materials from lignin. Prog. Biomass Bioenergy Res. 177.
Bono, P., 1994. Lignin as heat and light stabilizer in thermoplastics. FR 2 701 033.
Bono, P., Feldman, D., Banu, D., Lora, J.H., Wang, J., Wu, C.F., 1995. Degradable polymers and polymer products. WO 1995034604
Bono, P., Lambert, C., 1994. Degradable plastics film including lignin as active vegetable filler. US 5321065.
Bridgeman, T.G., Darvell, J.J.M., Williams, P.T., Fahmi, R., Bridgewater, A.V., Barraclough, T., Shield, I., Yates, N., Thain, S.C., Donnison, I.S., 2007. Influence of particle size on the analytical and chemical properties of two energy crops. Fuel 86, 60.
Buchholz, R.F., Quinn, D.W., 1994. Particulate fertilizer dust control. U.S. 5 360 465.
Caimi, P.G., 2004. Microbial hosts expressing foreign isoamylase genes and capable of utilizing starch degradation products as carbon sources in fermentation. WO 2004 018 645.
Camargo, F.A., Lemes, A.P., Moraes, S.G., Mei, L.I., Duran, N.,2002. Characterization and biodegradation of blend synthesize from natural polymers. In: 4th International symposium on Natural Polymers and Composites, Sao Pedro, Brazil, pp. 49-54.
Camargo, F.A., Lemes, A.P., Moraes, S.G., Mei, L.I., Duran, N.,2002. Characterization and biodegradation of blend synthesize from naturals Polymers. In: International symposium on Natural Polymers and Composites, Sao Carlos, Brazil, pp. 49-54.
Camargo, F.A., Lemes, A.P., Moraes, S.G., Mei, L.I., Duran, N., 2002. Characterization and biodegradation of blend synthesized from naturals polymers. Nat. Polym. Compos. IV, Proc. Int. Symp., 4th 49-54.
Casenave, S., Ait-Kadi, A., Riedl, B., 1996. Mechanical behavior of highly filled lignin/polyethylene composites made by catalytic grafting. Can. J. Chem. Eng. 74, 308.
Cetin, N.S., Ozman, N., 2002. Use of organosolv lignin in phenol-formaldehyde resins for particleboard production I. Organosolv lignin modified resins for particleboard production Int. J. Adhesion 22, 477.
Chakar, F.S., Ragauskas, A.J., 2004. Review of current and future softwood kraft lignin process chemistry. Industrial Crops and Products 20, 131-141.
Chaudhari, A., Ekhe, J.D., Deo, S., 2006. Non-isothermal crystallization behavior of lignin-filled polyethylene terephthalate (PET). Int. J. Polym. Anal. Charact. 11, 197.
Chen, C.L., 1991. Lignins: occurrence in woody tissues, isolation, reactions, and structure. Int. Fiber Sci. Technol. 11, 183.
Chen, H.Y., Bishop, M.T., Landes, B.G., Chum, S.P., 2006. Orientation and property correlations for LLDPE blown films. J. Appl. Polym. Sci. 101, 898-907.
220
Chen, M.J., Gunnells, D.W., Gardner, D.J., Meister, J.J., 1996. Utilization of chemically modified lignin. Book of Abstracts, 211th ACS National Meeting, New Orleans, LA, March 24-28 CELL-062.
Chen, M.J., Meister, J.J., Gunnells, D.W., Gardner, D.J., 1995. Alteration of the surface energy of wood using lignin-(1-phenylethene) graft copolymers. J. Wood Chem. Technol. 15, 287.
Chen, P., Zhang, L., Peng, S., Liao, B., 2006. Effects of nanoscale hydroxypropyl lignin on properties of soy protein plastics. J. Appl. Polymer Sci. 101, 334.
Chen, Y.-R., Sarkanen, S., 2006. From the macromolecular behavior of lignin components to the mechanical properties of lignin-based plastics. Cellul. Chem. Technol. 40, 149.
Cheng, X., Peng, D., Chen, Z., Chen, Y., 2005. Manufacture of concrete composite material containing high boiling alcohol lignin and its derivatives. CN 1 644 558.
Chiu, H.J., Chen, H.L., Lin, J.S., 2001. Crystallization induced microstructure of crystalline/crystalline poly(vinylidenefluoride)/poly(3-hydroxybutyrate) blends probed by small angle X-ray scattering. Polymer 42, 5749-5754.
Chodak, I., Brezny, R., Rychla, L., 1986. Blends of polypropylene with lignin. I. Influence of a lignin addition on crosslinking and thermooxidation stability of polypropylene. Chem. Pap. 40, 461.
Ciemniecki, S.L., Glasser, W.G., 1988. Multiphase materials with lignin: 1. Blends of hydroxypropyl lignin with poly(methyl methacrylate). Polymer 29, 1021.
Ciemniecki, S.L., Glasser, W.G., 1989. Polymer blends with hydroxypropyl lignin. ACS Symp. Ser. 397, 452.
Ciobanu, C., Ungureanu, M., Ignat, L., Ungureanu, D., Popa, V.I., 2004. Properties of lignin-polyurethane films prepared by casting method. Ind. Crops Prod. 20, 231.
Ciobanu, C., Ungureanu, M., Ignat, L., Ungureanu, D., Popa, V.I., 2004. Properties of lignin-polyurethane films prepared by casting method. Ind. Crops and Prod. 20, 231-241.
Clough, T.J., 1996. Copper and zinc recovery process from sulfide ores. U.S. 5 575 334.
Corti, A., Cristiano, F., Solaro, R., Chiellini, E., 2003. Biodegradable hybrid polymeric materials based on lignin and synthetic polymers. Biodegrad. Polym. Plast. 141.
Courchene, C.E., 1998. The tried, the true, and the new -- getting more pulp from chips -- modifications to the kraft process for increased yield. Breaking Pulp Yield Barrier Symp. 11.
Cruz, J.M., Dominguez, J.M., Dominguez, H., Parajo, J.C., 2001. Antioxidant and antimicrobial effects of extracts from hydrolysates of lignocellulosic materials. J. Agric. Food Chem. 49, 2459.
Cyr, N., Ritchie, R.G., 1989. Estimating the adhesive quality of lignins for internal bond strength. ACS Symp. Ser. 397 (Lignin: Properties and Materials), 372.
Da Cunha, C., Deffieux, A., Fontanille, M., 1993. Synthesis and polymerization of lignin-based macromonomers. III. Radical copolymerization of lignin-based macromonomers with methyl methacrylate. J. Appl. Polym. Sci. 48, 819.
221
Darie, R.N., Vasile, C., Cazacu, G., Kozlowski, M., 2007. Effect of lignin incorporation on some physico-chemical properties of blends containing synthetic polymers. Adv. Plast. Technol. 6/1-6/9.
Davin, L.B., Jourdes, M., Patten, A.M., Kim, K.-W., Vassao, D.G., Lewis, N.G., 2008. Dissection of lignin macromolecular configuration and assembly: comparison to related biochemical processes in allyl/propenyl phenol and lignan biosynthesis. Nat. Prod. Rep. 25, 1015.
De Oliveira, W., Glasser, W.G., 1990. Synthesis, chemistry and morphology of multiphase block copolymers containing lignin. Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.) 31, 655.
De Oliveira, W., Glasser, W.G., 1994a. Multiphase materials with lignin: 13. Block copolymers with cellulose propionate. Polymer 35, 1977.
De Oliveira, W., Glasser, W.G., 1994b. Multiphase materials with lignin. 11. Starlike copolymers with caprolactone. Macromolecules 27, 5.
De Oliveira, W., Glasser, W.G., 1994c. Multiphase materials with lignin. XII. Blends of poly(vinyl chloride) with lignin-caprolactone copolymers. J. Appl. Polym. Sci. 51, 563.
Deanin, R.D., Driscoll, S.B., Cook, R.J., Dubreuil, M.P., Hellmuth, W.N., Shaker, W.A., 1978. Lignin as a filler in commodity thermoplastics. Soc. Plast. Eng., Tech. Pap. 24, 711.
Dence, C.W., 1992. Determination of carboxyl groups by non-aqueous potentiometric titration. In: Lin, S.Y., Dence, C.W. (Eds.), Methods in Lignin Chemistry Springer, Berlin, Heidelberg, pp. 458-464.
Deng, X., Zhang, L., Xiong, C., 1993. Miscibility and crystallization behavior of biodegradable blend of poly(β -hydroxybutyrate) and poly(D,L-lactide)-co-poly(ethylene glycol). Chin. Chem. Lett. 4, 265-8.
Department of energys genomic, 1986, In. http://genomics.energy.gov. Detroit, W.J., Sanford, M.E., 1989. Oil well drilling cement dispersant. U.S. 4
846 888. Dixon, T.F., 1983. Combustion characteristics of bagasse suspension boilers.
Proc. Aust. Soc. Sugar Cane Technol. 5, 265. Dixon, T.F., Palmer, C., Domanti, S.D., 1987. Bagasse swirl burner
development. Proc. Aust. Soc. Sugar Cane Technol. 9, 295. Dobele, G., Dizhbite, T., Rossinskaja, G., Telysheva, G., Meier, D., Faix, O.,
2003. Pre-treatment of biomass with phosphoric acid prior to fast pyrolysis. A promising method for obtaining 1,6-anydrosaccharides in high yields. J. Anal. Appl. Pyrol. 68-69, 197.
Dobele, G., Meier, D., Faix, D.O., Radike, S., Rossinskaja, G., Telysheva, G., 2001. Volatile products of catalytic flash pyroysis of celluloses. J. Anal. Appl. Pyrol. 58-59, 453.
Docquier, S., Kevers, C., Lambe, P., Gaspar, T., Dommes, J., 2007. Beneficial use of lignosulfonates in in vitro plant cultures: stimulation of growth, of multiplication and of rooting. Plant Cell, Tissue Organ Cult. 90, 285.
Doherty, W.O.S., Halley, P., 2004. Lignin technology and market assessment for directing research in CRC sugar industry innovation project. SRI Job No. 3247.
Doherty, W.O.S., Mousavioun, P., Fellows, C.M., 2011. Value-adding to cellulosic ethanol: Lignin polymers. Ind. Crops prod. 33, 259-276.
222
Dong, J., Ozaki, Y., 1997. FTIR and FT-Raman Studies of Partially Miscible Poly(methyl methacrylate)/Poly(4-vinylphenol) Blends in Solid States. Macromolecules 30, 286-292.
Dumitrescu, L., Petrovici, V., Tica, R., Manciulea, I., 2002. Reducing the environment hazard using the lignosulfonates as copolymerization partners. Environ. Eng. Manage. J. 1, 437.
Ebata, Y., 2004. Environmentally friendly adhesives with improved resistance to heat and water and their manufacture. JP 2004 210 816.
Ede, R.M., Kilpelaeinen, I., 1995. Homo- and hetero-nuclear 2D NMR techniques: unambiguous structural probes for non-cyclic benzyl aryl ethers in soluble lignin samples. Res. Chem. Intermed. 21, 313.
El-Taweel, S.H., Stoll, B., Hoehne, G.W.H., Mansour, A.A., Seliger, H., 2004. Stress-strain behavior of blends of bacterial polyhydroxybutyrate. J. Appl. Polym. Sci. 94, 2528-2537.
El Raghi, S., Zahran, R.R., Gebril, B.E., 2000. Effect of weathering on some properties of poly(vinyl chloride)/lignin blends. Mater. Lett. 46, 332.
ElMiloudi, K., Djadoun, S., Sbirrazzuoli, N., Geribaldi, S., 2009. Miscibility and phase behaviour of binary and ternary homoblends of poly(styrene-co-acrylic acid), poly(styrene-co-N,N-dimethylacrylamide) and poly(styrene-co-4-vinylpyridine). Thermochim. Acta 483, 49-54.
Enoki, M., Aida, Y., 2007. Enzymic preparation of biodegradable lignin polyester copolymers. JP 2007 006 827.
Farmer, V.C., 1974. The infrared spectra of minerals, Mineralogical society, London.
Fasching, M., Schroeder, P., Wollboldt, R.P., Weber, H.K., Sixta, H., 2007. A new and facile method for isolation of lignin from wood based on complete wood dissolution. Holzforschung 62, 15-23.
Feldman, D., 2002. Lignin and its polyblends - a review. In: Hu, T.Q. (Ed.), Chemical Modification, Properties, and Usage of Lignin. Springer, New York, pp. 81-100.
Feldman, D., Banu, D., 1997a. Contribution to the study of rigid PVC polyblends with different lignins. J. Appl. Polym. Sci. 66, 1731-1744.
Feldman, D., Banu, D., 1997b. Lignin as a filler for PVC. Ext. Abstr. Eurofillers 97 211-213.
Feldman, D., Banu, D., 2003. Interactions in poly(vinyl chloride)-lignin blends. J. Adhes. Sci. Technol. 17, 2065.
Feldman, D., Banu, D., Campanelli, J., Zhu, H., 2001. Blends of vinylic copolymer with plasticized lignin: thermal and mechanical properties. J. Appl. Polym. Sci. 81, 861.
Feldman, D., Banu, D., Manley, R.S.J., Zhu, H., 2003. Highly filled blends of a vinylic copolymer with plasticized lignin: Thermal and mechanical properties. J. Appl. Polym. Sci. 89, 2000.
Feldman, D., Banu, D., Natansohn, A., Wang, J., 1991a. Structure-properties relations of thermally cured epoxy-lignin polyblends. J. Appl. Polymer Sci. 42, 1537.
Feldman, D., Banu, D., Wang, J., 1991b. Epoxy-lignin polyblends: Correlation between polymer interaction and curing temperature. J. Polymer Sci. 42, 1307.
Feldman, D., Khoury, M., 1988. Epoxy-lignin polyblends. Part II. Adhesive behavior and weathering. J.Adhesion Sci. and Technol. 2, 107.
223
Feldman, D., Lacasse, M.A., 1989, Morphology of lignin-polyurethane blends, In: Materials Research Society Symposium Proceedings, Canada.
Feldman, D., Luchian, C., Banu, D., Lacasse, M., 1991c. Polyurethane-maleic anhydride grafted lignin polyblends. Cellul. Chem. Technol. 25, 163-168.
Feldman, D.K., M., 1988. Epoxy-lignin polyblends. Part II. Adhesive behavior and weathering. J. Adh. Sci. Tech. 2, 107-116.
Ferry, J.D., 1980. Viscoelastic properties of polymers, 3rd ed. John Wiley, New York.
Fiske, L.B., 1992. Coal dust waste reduction. Residues Effluents: Process. Environ. Consid., Proc. Int. Symp. 871.
Fox, D.J., Gray, P.P., Dunn, N.W., Marsden, W.L., 1987. J. Chem. Tech. Biotechnol. 40, 117.
Fox, T.G., 1956. Influence of diluent and of copolymer composition on the glass temperature of a polymer system. Bull. Am. Phys. Soc. 2, 123.
Friedman, H.L., 1964. Kinetics of thermal degradation of char-forming plastics from thermogravimetry. Application to a phenolic plastic. J. Polym. Sci. Pol. Sym. 6, 183.
Frollini, E., Paiva, J.M.F., Trindade, W.G., Tanaka, I.A., Tanaka Razera, I.A., Tita, S.P., 2004. Plastics and composites from lignophenols. Nat. Fibers, Plast. Compos. 193.
Gandhi, K., Park, M., Sun, L., Zou, D., Li, C.X., Li, Y.D., Aklonis, J.J., Salovey, R., 1990. Model-filled polymers. II. Stability of polystyrene beads in a polystyrene matrix. J. Polym. Sci. Pol. Phys. 28, 2707-2714.
Garcìa-Pèrez, M., Chaala, A., Yang, J., Roy, C., 2001. Co-pyrolysis of sugarcane bagasse with petroleum residue. Part I: thermogravimetric analysis. Fuel 80, 1245-1258.
Gardner, D.J., McGinnis, G.D., 1988. Comparison of the reaction rates of the alkali-catalyzed addition of formaldehyde to phenol and selected lignins. J. Wood Chem. and Tech. 8, 261.
Gardner, D.J., Zhao, Z., Meister, J.J., 1993. Studies of the surface activity of lignin graft copolymers containing poly(methyl methacrylate) side chains. Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.) 34, 604.
Gargulak, J.D., Lebo, S.E., 2000. Commercial use of lignin-based materials. ACS Symp. Ser. 742, 304.
Ghaffar, A.M.E.A., 2002, Development of a biodegradable material based on Poly(3-hydroxybutyrate) PHB, In, Martin-Luther University, Wittenberg, pp. 115.
Ghosh, I., 1998, Blends of biodegradable thermoplastics with lignin esters, In, Virginia Polytechnic Institute and State University, VA, pp. 139.
Ghosh, I., Jain, R.K., Glasser, W.G., 1999. Multiphase materials with lignin. XV. Blends of cellulose acetate butyrate with lignin esters. J. Appl. Polym. Sci. 74, 448-457.
Ghosh, I., Jain, R.K., Glasser, W.G., 2000. Multiphase materials with lignin. Part 16. Blends of biodegradable thermoplastics with lignin esters. ACS Symp. Ser. 742, 331-350.
Glasser, W.G., Knudsen, J.S., Chang, C.S., 1988. Multiphase materials with lignin. III. Polyblends with ethylene-vinyl acetate copolymers. J. Wood Chem. Technol. 8, 221.
Glasser, W.G., Northey, R.A., Schultz, 1999. Lignin: Historical, Biological, and Material prespectives, Washing, DC.
224
Glasser, W.G., Wang, H.X., 1989. Derivatives of lignin and ligninlike models with acrylate functionality. ACS Symp. Ser. 397, 515.
Gogotov, A.F., 2000. Use of lignin derivatives as oxidants for production of aromatic aldehydes from lignin. Zh. Prikl. Khim. (S.-Peterburg) 73, 511.
Goncharov, V.M., Lesik, E.I., Khudolei, M.A., 2001. Modification of carbon black with substances based on vegetable polyphenols. Kauch. Rezina 17.
Gosselink, R.J.A., Abächerli, A., Semke, H., Malherbe, R., Käuper, P., Nadif, A., van Dam, J.E.G., 2004. Analytical protocols for characterisation of sulphur-free lignin. Ind. Crops Prod. 19, 271-281.
Grassie, N., Murray, E.J., Holmes, P.A., 1984. The thermal degradation of poly(β-hydroxybutyric acid): Part 2--Changes in molecular weight. Polym. Degrad. Stab. 6, 95-102.
Grassie, N., Murray, E.J., Holmes, P.A., 1984. The thermal degradation of poly(β-hydroxybutyric acid): Part 3--The reaction mechanism. Polym. Degrad. Stab. 6, 127-134.
Gratzl, J.S., Chen, C.L., 2000. Chemistry of pulping: lignin reactions. ACS Symp. Ser. 742, 392.
Graupner, N., 2008. Application of lignin as natural adhesion promoter in cotton fibre-reinforced poly(lactic acid) (PLA) composites J. Mater. Sci. 43, 5222.
Gregorová, A., Cibulková, Z., Kosíková, B., Simon, P., 2005. Stabilization effect of lignin in polypropylene and recycled polypropylene. . Polym. Degrad. Stabil. 89, 553.
Griffith, W.L., Compere, A.L., Leitten, C.F., Jr., Shaffer, J.T., 2003, Low-cost, lignin-based carbon fiber for transportation applications, In: International SAMPE Technical Conference, Society for the Advancement of Material and Process Engineering, USA.
Gundersen, S.A., Saether, O., Sjoblom, J., 2001. Salt effects on lignosulfonate and kraft lignin stabilized O/W-emulsions studied by means of electrical conductivity and video-enhanced microscopy. Colloids Surf., A 186, 141.
Guo, L., Sato, H., Hashimoto, T., Ozaki, Y., 2010. FTIR study on hydrogen-bonding interactions in biodegradable polymer blends of poly(3-hydroxybutyrate) and pol(4-vinylphenol). Macromolecules 43, 3897-3907.
Hablot, E., Bordes, P., Pollet, E., Avérous, L., 2008. Thermal and thermo-mechanical degradation of poly(3-hydroxybutyrate)-based multiphase systems. Polym. Degrad. Stab. 93, 413-421.
Hale, N., Xu, M., 1997. Low energy heat activated transfer printing process. U.S. 5 640 180.
Hasegawa, D., Teramoto, Y., Nishio, Y., 2008. Molecular complex of lignosulfonic acid/poly(vinyl pyridine) via ionic interaction: characterization of chemical composition and application to material surface modifications. J. Wood Sci. 54, 143.
Hasirci, V., 2003. Poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) based tissue engineering matrices. J. M. Sci.: Materials in Medicine 14, 121-126.
Hatakeyama, H., Hatakeyama, T., 2005. Environmentally compatible hybrid-type polyurethane foams containing saccharide and lignin components. Macromol. Symp. 224, 219.
225
Hatakeyama, H., Izuta, Y., Hirose, S., Hatakeyama, T., 1998. Polyurethanes derived from lignin-based polycaprolactones. Adv. Lignocellul. Chem. Ecol. Friendly Pulping Bleaching Technol., Eur. Workshop Lignocellul. Pulp, 5th 607.
Hatakeyama, H., Izuta, Y., Yoshida, T., Hirose, S., Hatakeyama, T., 2001a. Saccharide- and lignin-based polycaprolactones and polyurethanes. Recent Adv. Environ. Compat. Polym., Int. Cellucon Conf., 11th 33-46.
Hatakeyama, H., Nakayachi, A., Hatakeyama, T., 2005. Thermal and mechanical properties of polyurethane-based geocomposites derived from lignin and molasses. Composites, Part A 36A, 698.
Hatakeyama, T., Izuta, Y., Hirose, S., Hatakeyama, H., 2001b. Phase transitions of lignin-based polycaprolactones and their polyurethane derivatives. Polymer 43, 1177-1182.
Hechenleitner, A.A.W., Pineda, E.A.G., Martins, A.D., Alves, E., 1997. Thermal behavior of lignin-polystyrene and lignin-cellulose phthalate blends. Braz. Symp. Chem. Lignins Other Wood Compon., Proc., 5th 6, 315.
Henry, L.F., 1964. Kinetics of thermal degradation of char-forming plastics from thermogravimetry. Application to a phenolic plastic. J. Polym. Sci., Part C: Polym. Symp. 6, 183-195.
Henry, N.W., Dadmun, M.D., 2009. Model compatibilizers for the lignin-polystyrene interface. Abstracts of Papers, 237th ACS National Meeting, Salt Lake City, UT, United States, March 22-26, 2009 CELL-217.
Hiro-kuni, O., Kenichi, S., 1989. Wood adhesives from phenolysis lignin. ACS Symp. Ser. 397 (Lignin: Properties and Materials.), 334.
Hirose, S., 2006. Sugars and lignin as raw materials for epoxy resins. Kogyo Zairyo 54, 62.
Hirose, S., Hatakeyama, H., 2006. Synthesis and thermal properties of epoxy resins from alcoholysis lignin and glycerol. Kami Parupu Kenkyu Happyokai Koen Yoshishu 73rd, 150.
Hirose, S., Hatakeyama, H., Funabashi, M., 2002. Biodegradable polyvalent carboxylic acid and epoxy resin composition. JP 2002 284 791.
Hu, W.J., Harding, S.A., Lung, J., Popko, J.L., Ralph, J., Stokke, D.D., Tsai, C.J., Chiang, V.L., 1999. Repression of lignin biosynthesis promotes cellulose accumulation and growth in transgenic trees. Nat. Biotechnol. 17, 808.
Huang, J., Zhang, L., Chen, P., 2003. Effects of lignin as a filler on properties of Soy Protein plastics. II Alkaline lignin. J. Appl. Polymer Sci. 88, 3291.
Huang, J., Zhang, L., Wei, H., Cao, X., 2004. Soy protein isolate/kraft lignin composites compatibilized with methylene diphenyl diisocyanate. . J. Appl. Polymer Sci. 93, 624.
Huang, J., Zheng, H., Fan, L., Xu, Y., 2006. hydroxypropyl lignin-modified soybean protein plastics and its preparation method. CN 1 807 490.
Huttenrauch, R., 1971. Identification of hydrogen bonds in drug forms by means of deuterium exchange demonstration of binding forces in compressed cellulose forms. Die Pharmazie 26, 645.
Huttermann, A., Majcherczyk, A., Braun-Lullemann, A., Mai, C., Fastenrath, M., Kharazipour, A., Huttermann, J., Huttermann, A.H., 2000. Enzymic activation of lignin leads to an unexpected copolymerization with carbohydrates. Naturwissenschaften 87, 539.
226
Ibrahim, M.N.M., Azreena, I.N., Nadiah, M.Y.N., Saaid, I.M., 2006. Lignin graft copolymer as a drilling mud thinner for high temperature well. J. Appl. Sci. 6, 1808.
Ikejima, T., Cao, A., Yoshie, N., Inoue, Y., 1998. Surface composition and biodegradability of poly(3-hydroxybutyric acid)/poly(vinyl alcohol) blend films. Polym. Degrad. Stab. 62, 463-469.
Ikejima, T., Inoue, Y., 1999. Crystallization behavior and environmental biodegradability of the blend films of poly(3-hydroxybutyric acid) with chitin and chitosan. Carbohydr. Polym. 41, 351-356.
Innocentini-Mei, L.H., Bartoli, J.R., Baltieri, R.C., 2003. Mechanical and thermal properties of poly(3-hydroxybutyrate) blends with starch and starch derivatives. Macromol. Symp. 197, 77-87.
John, J., Bhattacharya, M., 1999. Properties of reactively blended soya protein and modified polyester. . Polymer Int. 48, 1165.
Jones, D.H., 2004. Wastewater treatment. U.S. 2004 144 719. Jones, D.H., 2008. Lignosulfonate-containing aqueous cleaning solutions and
methods for cleaning surfaces. WO 2008 046 174. Kadla, J.F., Kubo, S., 2003. Miscibility and Hydrogen Bonding in Blends of
Poly(ethylene oxide) and Kraft Lignin. Macromolecules 36, 7803-7811. Kadla, J.F., Kubo, S., 2004. Lignin-based polymer blends: analysis of
intermolecular interactions in lignin-synthetic polymer blends. Composites Part A 35, 395-400.
Kadla, J.F., Kubo, S., Venditti, R.A., Gilbert, R.D., Compere, A.L., Griffith, W., 2002. Lignin-based carbon fibers for composite fiber applications. Carbon 40, 2913-2920.
Kagawa, I., Sukai, K., 1956. Crystallinity and heat of combustion of cellulose. Kogyo Kagaku Zasshi 59, 797.
Ke, T., Sun, S.X., Seib, P., 2003. Blending of poly(lactic acid) and starches containing varying amylose content. Journal of Applied Polymer Science 89, 3639-3646.
Kelley, S.S., Glasser, W.G., Ward, T.C., 1989. Multiphase materials with lignin. 9. Effect of lignin content on interpenetrating polymer network properties. Polymer 30, 2265.
Kelley, S.S., Ward, T.C., Glasser, W.G., 1990. Multiphase materials with lignin. VIII. Interpenetrating polymer networks from polyurethanes and poly(methyl methacrylate). J. Appl. Polym. Sci. 41, 2813.
Kelly, J.R., 1983. Drilling fluid composition. U.S. 4 374 738. Khabarov, Y.G., Koshutina, N.N., Shergin, A.E., 2001. Manufacture of alkali-
soluble iron chelates with nitrosated lignosulfonic acid. RU 2 165 936. Khan, M.A., Ashraf, S.M., 2006. Development and characterization of
groundunt shell lignin modified phenol formaldehyde wood adhesive. Indian J. Chem. Technol. 13, 347.
Khan, M.A., Ashraf, S.M., 2007. Studies on thermal characterization of lignin. Substituted phenol formaldehyde resin as wood adhesives. J. Therm. Anal. Calorim. 89, 993.
Khelfa, A., Finqueneisel, G., Auber, M., Weber, J.V., 2008. Influence of some minerals on the cellulose thermal degradation mechanisms. Thermogravimetric and pyrolysis-mass spectrometry studies. J. Thermal Anal. Calorim. 92, 793.
227
Kikkawa, Y., Suzuki, T., Tsuge, T., Kanesato, M., Doi, Y., Abe, H., 2006. Phase structure and enzymatic degradation of poly(L-lactide)/atactic poly(3-hydroxybutyrate) blends: an atomic force microscopy study. Biomacromolecules 7, 1921-8.
Kim, Y., Mosier, N.S., Ladisch, M.R., 2009. Enzymatic digestion of liquid hot water pretreated hybrid poplar. Biotechnol. Prog. 25, 340-348.
Kirk, T.K., 1971. Effects of microorganisms on lignin. Annual Review of Phytopathology 9, 185-210.
Koljonen, K., Österberg, M., Kleen, M., Fuhrmann, A., Stenius, P., 2004. Precipitation of lignin and extractives on kraft pulp: effect on surface chemistry, surface morphology and paper strength. Cellulose 11, 209-224.
Kollman, F.F.P., Topf, P., 1971. Fire Flammability 2, 231. Kordsachia, O., Patt, R., Sixta, H., 1999. Cellulose isolation from various raw
materials. Papier (Heidelberg) 53, 96. Koshijima, T., Muraki, E., 1964. Radiation grafting of methyl methacrylate onto
lignin. Mokuzai Gakkaishi 10, 110. Kosikova, B., Alexy, P., Gregorova, A., 2003. Use of lignin products derived
from wood pulping as environmentally desirable component of composite rubber materials. Wood Res. (Bratislava, Slovakia) 48, 62.
Košíková, B., Alexy, P., Mikulášová, M., Kačík, F., 2001. Characterization of biodegradability of lignin-polyethylene blends. Wood research 46, 31-36
Kosikova, B., Demianova, V., 1992. Lignin-filled UV-absorbing polyolefin film. CS 277 055.
Kosikova, B., Demianova, V., Kacurakova, M., 1993. Sulfur-free lignins as composites of polypropylene films. J. Appl. Polym. Sci. 47, 1065.
Koufopanos, C.A., Maschio, G., Lucchesi, A., 1989. Kinetic modelling of the pyrolysi of biomass and biomass components. Can. J. Chem. Eng. 67, 75.
Kramarova, Z., Alexy, P., Chodak, I., Spirk, E., Hudec, I., Kosikova, B., Gregorova, A., Suri, P., Feranc, J., Bugaj, P., Duracka, M., 2007. Biopolymers as fillers for rubber blends. Polym. Adv. Technol. 18, 135.
Krizkova, L., Polonyi, J., Kosikova, B., Dobias, J., Belicova, A., Krajcovic, J., Ebringer, L., 2000. Lignin reduces ofloxacin-induced mutagenicity in Euglena assay. Anticancer Res. 20, 833.
Kubat, J., Stroemvall, H.E., 1983. Properties of injection molded lignin-filled polyethylene and polystyrene. Plast. Rubber Process. Appl. 3, 111.
Kubo, S., Gilbert, R.D., Kadla, J.F., 2005. Lignin-based polymer blends and biocomposite materials. Nat. Fibers, Biopolym., Biocompos. 671.
Kubo, S., Kadla, J.F., 2003. The formation of strong intermolecular interactions in immiscible blends of poly(vinyl alcohol) (PVA) and lignin. Biomacromolecules 4, 561.
Kubo, S., Kadla, J.F., 2004. Poly(ethylene oxide)/organosolv lignin blends: relationship between thermal properties, chemical structure, and blend behavior. Macromolecules 37, 6904.
Kubo, S., Kadla, J.F., 2005. Kraft lignin/poly(ethylene oxide) blends: Effect of lignin structure on miscibility and hydrogen bonding. J. Appl. Polym. Sci. 98, 1437.
Kubo, S., Kadla, J.F., Gilbert, R.D., 2002, Thermal-blending of lignin with hydrophilic polymers, In: 223rd ACS National Meeting, American Chemical Society, USA.
228
Kukkola, E.M., Koutaniemi, S., Poellaenen, E., Gustafsson, M., Karhunen, P., Lundell, T.K., Saranpaeae, P., Kilpelaeinen, I., Teeri, T.H., Fagerstedt, K.V., 2004. The dibenzodioxocin lignin substructure is abundant in the inner part of the secondary wall in Norway spruce and silver birch xylem. Planta 218, 497.
Kulshreshtha, A.K., Vasile, C., 2002. Handbook of polymer blends and composites, Rapra Technology, Shrewsbury.
Kumagai, Y., Doi, Y., 1992. Enzymatic degradation and morphologies of binary blends of microbial poly(3-hydroxy butyrate) with poly(ε-caprolactone), poly(1,4-butylene adipate and poly(vinyl acetate). Polym. Degrad. Stab. 36, 241-248.
Kunanopparat, T., Menut, P., Morel, M.H., Guilbert, S., 2009. Modification of the wheat gluten network by kraft lignin addition. J. Agric. Food Chem. 57, 8526-8533.
Kuo, S.W., Chan, S.C., Chang, F.C., 2002. Miscibility enhancement on the immiscible binary blend of poly(vinyl acetate) and poly(vinyl pyrrolidone) with bisphenol A. Polymer 43, 3653-3660.
Kuo, S.W., Chang, F.C., 2001. Effects of Copolymer Composition and Free Volume Change on the Miscibility of Poly(styrene-co-vinylphenol) with Poly(ε-caprolactone). Macromolecules 34, 7737-7743.
Kurian, J.V., 2005. A new polymer platform for the future - sorona from corn derived 1,3-propanediol. J. Polym. Environ. 13, 159.
Kurian, J.V., Liang, Y., 2008. Processes for making elastomeric polyether esters from recycled polyesters. WO 2008 085 397.
Lamb, B.W., Bilger, R.W., 1977. Combustion of bagasse: literature review. Sugar Technol. Rev. 4, 89.
Lapierre, C., Pollet, B., Petit-Conil, M., Toval, G., Romero, J., Pilate, G., Leple, J.C., Boerjan, W., Ferret, V., De Nadai, V., Jouanin, L., 1999. Structural alterations of lignins in transgenic poplars with depressed cinnamyl alcohol dehydrogenase or caffeic acid O-methyltransferase activity have an opposite impact on the efficiency of industrial kraft pulping. Plant Physiol. 119, 153.
Lazic, V., Kules, M., Ibrahimefendic, S., 1986. The mixing of natural rubber with lignins and its effect on physical and mechanical properties. Hem. Ind. 40, 14.
Lebo, S.E., 1996. Methods for producing improved pesticides. 5 529 772. Lemoigne, M., 1926 Products of dehydration and of polymerization of β-
hydroxybutyric acid. Bull. Soc. Chim. Belg. 8, 770-82. Lepifre, S., Baumberger, S., Pollet, B., Cazaux, F., Coqueret, X., Lapierre, C.,
2004. Reactivity of sulphur-free alkali lignins within starch films. Ind. Crops Prod. 20, 219.
Lepifre, S., Froment, M., Cazaux, F., Houot, S., Lourdin, D., Coqueret, X., Lapierre, C., Baumberger, S., 2004. Lignin incorporation combined with electron-beam irradiation improves the surface water resistance of starch films. Biomacromolecules 5, 1678.
Levon, K., Huhtala, J., Malm, B., Lindberg, J.J., 1987. Improvement of the thermal stabilization of polyethylene with lignosulfonate. Polymer 28, 745.
229
Li, J., He, Y., Inoue, Y., 2003. Thermal and mechanical properties of biodegradable blends of poly(L-lactic acid) and lignin. Polymer Int. 52, 949.
Li, S.D., He, J.D., Yu, P.H., Cheung, M.K., 2003. Thermal degradation of poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) as studied by TG, TG–FTIR, and Py–GC/MS. J. Appl. Polym. Sci. 89, 1530-1536.
Li, X.F., Luo, X.G., 2005. Effect of LDPE-g-MAH on properties of LDPE/lignin blends. Zhongguo Suliao 19, 41.
Li, Y., Mlynar, J., Sarkanen, S., 1997. The first 85% kraft lignin-based thermoplastics. J. Polym. Sci., Part B: Polym. Phys. 35, 1899.
Li, Y., Sarkanen, S., 2002. Alkylated kraft lignin-based thermoplastic blends with aliphatic polyesters. Macromolecules 35, 9707.
Li, Y., Sarkanen, S., 2003. Biodegradable Kraft lignin-based thermoplastics. Biodegradable Polymers and Plastics, [Proceedings of the World Conference on Biodegradable Polymers & Plastics], 7th, Terrenia, Italy, June 4-8, 2002 121.
Li, Y., Sarkanen, S., 2005. Miscible blends of kraft lignin derivatives with low-Tg polymers. Macromolecules 38, 2296.
Lim, S.P., Gan, S.N., Tan, I., 2005. Degradation of medium-chain-length polyhydroxyalkanoates in tropical forest and mangrove soils. Appl. Biochem. Biotech. 126, 23-33.
Lin, A.A., Kwei, T.K., Reiser, A., 1989. On the physical meaning of the Kwei equation for the glass transition temperature of polymer blends. Macromolecules 22, 4112-4119.
Lin, S.Y., Bushar, L.L., 1991. Lignosulfonate-based wood preservatives. U.S. 4 988 576.
Lipatov, Y., S., Nesterov, A.E., 1997. Thermodynamics of polymer blends Technomic, Lancaster, PA
Liu, G., Qiu, X., Xing, D., Yang, D., 2006. Phenolation modification of wheat straw soda lignin and its utilization in lignin-based phenolic formaldehyde resins. Research Progress in Pulping and Papermaking, [International Symposium on Emerging Technologies of Pulping and Papermaking], 3rd, Guangzhou, China, Nov. 8-10, 2006 933.
Liu, G., Qiu, X., Yang, D., 2008. Properties of wheat straw soda lignin of different molecular weights and its influence on properties of LPF adhesive. Huagong Xuebao (Chin. Ed.) 59, 1590.
Liu, J., Qiu, Z., Jungnickel, B.J., 2004. Crystallization and morphology of poly(vinylidene fluoride)/poly(3-hydroxybutyrate) blends. III. Crystallization and phase diagram by differential scanning calorimetry. J. Polym. Sci., Part B: Polym. Phys. 43, 287-295.
Liu, Q., Yang, S., Li, J., Zhan, H., 2002. Characteristics of oxygen-alkali lignin and its application in synthesis of polyurethane. Emerging Technol. Pulping Papermaking, Proc. Int. Symp., 2nd 841.
Loffler, G., Wargadalam, V.J., Winter, F., 2002. Catalytic effect of biomass ash on CO, CH4 and HCN oxidation under fluidised bed combustor conditions. Fuel 81, 711.
Lora, J.H., 2002. Chemical modification. In: Hu, T. (Ed.), Properties and usage of lignin. Springer, New York.
230
Lora, J.H., Glasser, W.G., 2002. Recent industrial application of lignin. J. polym. and env. 10, 39-48.
Lora, J.H., Trojan, M.J., Klingensmith, W.H., 1991. Lignin derivatives as tackifiers for rubber compositions. EP 461 463.
Lu, F.J., Chu, L.H., Gau, R.J., 1998. Free radical-scavenging properties of lignin. Nutr. Cancer 30, 31.
Luo, M., Stanmore, B., 1992. Combustion characteristics of bagasse. Proc. Aust. Soc. Sugar Cane Technol. 14, 316.
Maelkki, Y., Toikka, M.M., Sipilae, A.J., 2002. Manufacture of absorbing substances from lignocellulosic materials and acrylic monomers. WO 2002 092 669.
Mahendrasingam, A., Martin, C., Fuller, W., Blundell, D.J., MacKerron, D., Rule, R.J., Oldman, R.J., Liggat, J., Riekel, C., Engstrom, P., 1995. Microfocus X-ray Diffraction of Spherulites of Poly-3-hydroxybutyrate. J. Synchr. Rad. 2, 308-312.
Mai, C., Majcherczyk, A., Huttermann, A., 2000b. Chemo-enzymatic synthesis and characterization of graft copolymers from lignin and acrylic compounds. Enzyme Microb. Technol. 27, 167.
Mai, C., Milstein, O., Huttermann, A., 2000a. Chemoenzymatical grafting of acrylamide onto lignin. J. Biotechnol. 79, 173.
Mai, C., Schormann, W., Huttermann, A., 2001. Chemo-enzymatically induced copolymerization of phenolics with acrylate compounds. Appl. Microbiol. Biotechnol. 55, 177.
Mai, C., Schormann, W., Huttermann, A., Kappl, R., Huttermann, J., 2002. The influence of laccase on the chemo-enzymatic synthesis of lignin graft-copolymers. Enzyme Microb. Technol. 30, 66.
Maki, M., Leung, K.T., Qin, W., 2009. The prospects of cellulase-producing bacteria for the bioconversion of lignocellulosic biomass. International Journal of Biological Sciences 5, 500-516.
Mansour, O.Y., 1992. Thermal degradation of some thermoplastic polymers in presence of lignin. Polym. Plast. Technol. Eng. 31, 747.
Mansouri, N.-E., Pizzi, A., Salvado, J., 2007. Lignin-based wood panel adhesives without formaldehyde. Holz Roh- Werkst. 65, 65.
Meier, J.N., Fyles, J.W., MacKenzie, A.F., O'Halloran, I.P., 1993. Effects of lignosulfonate-fertilizer applications on soil respiration and nitrogen dynamics. Can. J. Soil Sci. 73, 233.
Meister, J.J., Aranha, A., Wang, A., 1993. Poly(3-hydroxybutyrate)-(3-hydroxyvalerate)-lignin graft copolymer blends. Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.) 34, 608.
Meister, J.J., Lathia, A., Chang, F.F., 1991. Solvent effects, species and extraction method effects, and coinitiator effects in the grafting of lignin. J. Polym. Sci., Part A: Polym. Chem. 29, 1465.
Meister, J.J., Li, C.T., 1990. Synthesis of cationic graft copolymers of lignin. Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.) 31, 653.
Meister, J.J., Zhao, Z., 1992. Lignin graft copolymers containing a methyl methacrylate graft side chain. Polym. Mater. Sci. Eng. 67, 228.
Mihaela, C., Vasile, C., Agafitei, G.E., Cazacu, G., Stoleriu, A., 2010. Compatibility and degradability of the polyalkanoates/epoxy modified lignin blends Polym. Yearb. 23, 265-282.
231
Miidla, H., 1980. Lignification in plants and methods for its study. Regul. Rosta Pitan. Rast. 87.
Millili, G.P., Schwartz, J.B., 1990. The strength of microcrystalline cellulose pellets: The effect of granulating with water/ethanol mixtures. Drug Dev. Ind. Pharm. 16, 1411.
Millili, G.P., Wigent, R.J., Schwartz, J.B., 1996. Differences in the mechanical strength of dried microcrystalline cellulose pellets are due to significant changes in the degree of hydrogen bonding. Pharm. Dev. Technol. 1, 239.
Milstein, O., Gersonde, R., Huttermann, A., Chen, M.-J., Meister, J.J., 1996. Fungal biodegradation of lignin graft copolymers from ethene monomers. J. Macromol. Sci., Pure Appl. Chem. A33, 685.
Milton, F., 1995, The Preservation of Wood. A Self Study Manual for Wood Treaters, College of Natural Resources, In, Minnesota Extension Service, University of Minnesota College of Natural Resources, St. Paul, MN, USA pp. 102.
Mishra, S.B., Mishra, A.K., Kaushik, N.K., Khan, M.A., 2007. Study of performance properties of lignin-based polyblends with polyvinyl chloride. J. Mater. Process. Technol. 183, 273.
Moerck, R., Yoshida, H., Kringstand, K.P., Hatakeyama, H., 1986. Fractionation of kraft lignin by successive extraction with organic solvents, 1. Functional groups, 13C-NMR-spectra and molecular weight distributions. Holzforschung 40, 51-60.
Mosier, N., Wyman, C., Dale, B., Elander, R., Lee, Y.Y., Holtzapple, M., Ladisch, M., 2005. Features of promising technologies for pretreatment of lignocellulosic biomass. Bioresource Technol. 96, 673.
Mousavioun, P., Doherty, W.O.S., 2010. Chemical and thermal properties of fractionated bagasse soda lignin. Ind. Crops Prod. 31, 52-58.
Mousavioun, P., Doherty, W.O.S., George, G., 2010. Thermal stability and miscibility of poly(hydroxybutyrate) and soda lignin blends. Ind. Crops Prod. 32, 656-661.
Moxley, G., Zhu, Z., Zhang, Y.H.P., 2008. Efficient sugar release by the cellulose solvent-based lignocellulose fractionation technology and enzymatic cellulose hydrolysis. J. Agric. Food Chem. 56, 7885-7890.
Muller, P.C., Glasser, W.G., 1984. Engineering plastics from lignin. VIII. phenolic resin prepolymer synthesis and analysis. J. Adhes. 17, 157.
Muller, P.C., Kelley, S.S., Glasser, W.G., 1984. Engineering plastics from lignin. IX. phenolic resin synthesis and characterization. The Journal of Adhesion 17, 185 - 206.
Nada, A.A., Abou-Youssef, H., El-Gohary, S., 2003. Phenol formaldehyde resin modification with lignin. Polym.-Plast. Technol. Eng. 42, 689.
Naegele, H., Pfitzer, J., Eisenreich, N., Eyerer, P., Elsner, P., Eckl, W., 2000. Plastic material made from polymer blend Denmark WO 0027923.
Nagahama, M., Takebayashi, K., 2005. Recent trend of biodegradable plastics. Kagaku Sochi 47, 81-86.
Nagele, H., Pfitzer, J., Eisenreich, N., Eyerer, P., Elsner, P., Eckl, W., 2000. Plastic blends containing lignin-based natural polymers and their use. WO 2000 027 923.
Narayan, R., Stacy, N., Ratcliff, M., Chum, H.L., 1989. Engineering lignopolystyrene materials of controlled structures. ACS Symp. Ser. 397, 476.
232
Nassar, M.M., 1999. Thermal analysis kinetics of bagasse and rice straw. Energy Sources 21, 131.
Nassar, M.M., Ashour, E.A., Wahid, S.S., 1996. Thermal Characteristics of Bagasse. J. Appl. Polym. Sci. 61, 885.
Niemi, K., Kevers, C., Haeggman, H., 2005. Lignosulfonate promotes the interaction between Scots pine and an ectomycorrhizal fungus Pisolithus tinctorius in vitro. Plant Soil 271, 243.
Nitz, H., Semke, H., Landers, R., Mulhaupt, R., 2001a. Reactive extrusion of polycaprolactone compounds containing wood flour and lignin. J. Appl. Polym. Sci. 81, 1972-1984.
Nitz, H., Semke, H., Mulhaupt, R., 2001b. Influence of lignin type on the mechanical properties of lignin based compounds. Macromol. Mater. Eng. 286, 737-743.
Nonaka, Y., Tomita, B., Hatano, Y., 1996. Viscoelastic properties of lignin/epoxy resins and their adhesive strength. Mokuzai Kogyo 51, 250.
Nonaka, Y., Tomita, B., Hatano, Y., 1997. Synthesis of lignin/epoxy resins in aqueous systems and their properties. Holzforschung 51, 183.
Northey, R.A., 2002. The use of lignosulfonates as water reducing agents in the manufacture of gypsum wallboard. Chem. Modif., Prop., Usage Lignin 139.
NREL, 2008, Determination of structural carbohydrates and lignin in biomass, In, Colorado.
Oehgren, K., Vehmaanperae, J., Siika-Aho, M., Galbe, M., Viikari, L., Zacchi, G., 2007. High temperature enzymatic prehydrolysis prior to simultaneous saccharification and fermentation of steam pretreated corn stover for ethanol production. Enzyme and Microbial Technology 40, 607-613.
Okabe, Y., Mizuno, K., Hirano, K., Fukuda, H., Oda, M., Ishigaki, T., Harada, T., 2006. Manufacture of cellulosic fiberboards. JP 2006 007 534.
Olivares, M., Guzman, J.A., Natho, A., Saavedra, A., 1988. Kraft lignin utlization in adhesives. . Wood Sci., Technol. 22, 157.
Olm, L., Tisdat, G., 1979. Kinetics of the initial stage of kraft pulping. Svensk Cellulosa 82, 458-464.
Otaigbe, J.U., Adams, D.O., 1997. Bioadsorbable soy protein plastic composites. Effect of polyphosphate fillers on water absorption and mechanical properties. . J, Environment. Polym. Degrad. 5, 199.
Ouyang, X., Qiu, X., Lou, H., Yang, D., 2006. Corrosion and scale inhibition properties of sodium lignosulfonate and its potential application in recirculating cooling water system. Ind. Eng. Chem. Res. 45, 5716.
Pan, X., Kadla, J.F., Ehara, K., Gilkes, N., Saddler, J.N., 2006. Organosolv ethanol lignin from hybrid poplar as a radical scavenger: relationship between lignin structure, extraction conditions, and antioxidant activity. J. Agric. Food Chem. 54, 5806.
Pandey, A., Soccol, C.R., Nigam, P., Soccol, V.T., 2000. Biotechnological potential of agro-industrial residues. I: sugarcane bagasse. Bioresource Technol. 74, 69-80.
Pandey, K.K., 1999. A study of chemical structure of soft and hardwood and wood polymers by FTIR spectroscopy. J. Appl. Polym. Sci. 71, 1969–1975.
233
Park, Y., Doherty, W.O.S., Halley, P., 2008. Developing new lignin-based coatings and composites. Ind. Crop. Prod. 27, 1163-1167.
Pavlov, D., Myrvold, B.O., Rogachev, T., Matrakova, M., 2000. A new generation of highly efficient expander products and correlation between their chemical composition and the performance of the lead-acid battery. J. Power Sources 85, 79.
Pavol, A., Bozcaron, K., Gabriela, C., Adriána, G., Pavol, M., 2004. Modification of lignin-polyethylene blends with high lignin content using ethylene-vinylacetate copolymer as modifier. J. Appl. Polym. Sci. 94, 1855-1860.
Peng, W., Riedl, B., 1994. The chemorheology of phenol-formalddehye thermoset resin and mixtures of the resin with lignin fillers. Polymer 35, 1280.
Phillips, R.B., Brown, W., Stannett, V.T., 1972. Graft copolymerization of styrene and lignin. II. Kraft softwood lignin. J. Appl. Polym. Sci. 16, 1.
Piaskiewicz, M., Rajkiewicz, M., Gesiak, M., Berek, I., Kleps, T., 1998. Use of waste lignin in rubber blends. Elastomery 2, 43.
Piccolo, R.S.J., Santos, F., Frollini, E., 1997. Sugar cane bagasse lignin in resol type resin: alternative application for lignin-phenol formaldehyde resins. J. Macromol. Sci. - Pure Appl. Chem. A34, 153.
Pivinskii, Y.E., Dyakin, P.V., Dyakin, P.V., 2006. Pressure-molded high-alumina ceramic castables. 3. Effect of processing additives on pressure-induced compaction and properties of bauxite-quartz glass matrix systems. Refract. Ind. Ceram. 47, 132.
Pizzi, A., 2003. Natural phenolic adhesives II: Lignin. Handbook of Adhesive Technology (2nd Edition, Revised and Expanded).
Pizzoli, M., Scandola, M., Ceccorulli, G., 1994. Crystallization kinetics and morphology of poly(3-hydroxybutyrate)/cellulose ester blends. Macromolecules 27, 4755-4761.
Potapov, G.P., Nikulina, L.A., Fedorova, E.I., 1990. Chemical modification of hydrolytic lignin by sodium acrylate. Khim. Drev. 40-3.
Pouteau, C., Baumberger, S., Cathala, B., Dole, P., 2004. Lignin-polymer blends: evaluation of compatibility by image analysis. Comptes Rendus Biologies 327, 935-943.
Pseja, J., Charvatova, H., Hruzik, P., Hrncirik, J., Kupec, J., 2006. Anaerobic biodegradation of blends based on polyvinyl alcohol. J. Polym. Environ. 14, 185.
Pucciariello, R., Bonini, C., D'Auria, M., Villani, V., Giammarino, G., Gorrasi, G., 2008. Polymer blends of steam-explosion lignin and poly(ε-caprolactone) by high-energy ball milling. J. Appl. Polym. Sci. 109, 309.
Pucciariello, R., Villani, V., Bonini, C., D'Auria, M., Vetere, T., 2004. Physical properties of straw lignin-based polymer blends. Polymer 45, 4159.
Quideau, S., Ralph, J., 1992. Facile large-scale synthesis of coniferyl, sinapyl, and p-coumaryl alcohol. J. Agric. Food Chem. 40, 1108-1110.
Rainey, T.J., 2009, A study into the permeability and compressibility properties of Australian bagasse pulp, In: School of Engineering systems, Queensland University of Technology, Brisbane, Australia, pp. null.
Ralph, J., Lundquist, K., Brunow, G., Lu, F., Kim, H., Schatz, P.F., Marita, J.M., Hatfield, R.D., Ralph, S.A., Christensen, J.H., Boerjan, W., 2004.
234
Lignins: Natural polymers from oxidative coupling of 4-hydroxyphenylpropanoids. Phytochem. Rev. 3, 29.
Raskin, M., Ioffe, L.O., Pukis, A.Z., Wolf, M.H., 2002. Lignin-based resin materials for industrial binders and method of producing same. U.S. 2002 065 400.
Rattanachomsri, U., Tanapongpipat, S., Eurwilaichitr, L., Champreda, V., 2009. Simultaneous non-thermal saccharification of cassava pulp by multi-enzyme activity and ethanol fermentation by Candida tropicalis. Journal of Bioscience and Bioengineering 107, 488-493.
Raveendran, K., Ganesh, A., Khilar, K., 1996. Pyrolysis characteristics of biomass and biomass components. Fuel 75, 987.
Reddy, C.S.K., Ghai, R., Rashmi, Kalia, V.C., 2003. Polyhydroxyalkanoates: an overview. Bioresour. Technol. 87, 137-146.
Reich, W., Breitenbach, J., Larbig, H., Beck, E., 1996. Preparation of coatings from radiation-curable compositions containing polymerizable lignin derivatives. DE 4 437 720.
Reti, C., Casetta, M., Duquesne, S., Bourbigot, S., Delobel, R., 2008. Flammability properties of intumescent PLA including starch and lignin. Polym. Adv. Technol. 19, 628.
Reveendran, K., Ganesh, A.K., Khilar, C., 1995. Influence of mineral matter on biomass pyrolysis chars. Fuel 74, 1812.
Richards, G.N., Shafizadeh, F., 1978. Mechanism of thermal degradation of sucrose. A preliminary study. Aust. J. Chem. 31, 1825.
Rizk, N.A., Nagaty, A., Mansour, O.Y., 1984. Inhibition and retardation induced by lignin on homopolymerization reactions of some vinyl monomers. Acta Polym. 35, 61.
Robert, D.R., Bardet, M., Gellerstedt, G.r., Lindfors, E.L., 1984. Structural Changes in Lignin During Kraft Cooking Part 3. On the Structure of Dissolved Lignins. J. W. Chem. and Tech. 4, 239-263.
Sailaja, R.R.N., 2005. Low density polyethylene and grafted lignin polyblends using epoxy-functionalized compatibilizer: Mechanical and thermal properties. Polym. Int. 54, 1589.
Sakakibara, A., Takeyama, H., Morohoshi, N., 1966. Hydrolysis of lignin with dioxane and water. IV. Experiments with methylated lignin and certain model compounds. Holzforschung 20, 45.
Saraf, V.P., Glasser, W.G., 1984. Engineering plastics from lignin. III. Structure property relationships in solution cast polyurethane films. Journal of Applied Polymer Science 29, 1831-1841.
Sarkanen, S., Li, Y., 1999. Plasticizers that transform alkylated kraft lignins into thermoplastics. Biomass, Proc. Biomass Conf. Am., 4th 1, 533.
Satyanarayana, K.G., Arizaga, G.G.C., Wypych, F., 2009. Biodegradable composite based on lignocellulosic fibers - An overview. Prog. Polym. Sci. 34, 982.
Savel'eva, M.B., Onishchenko, Z.V., Bogomolov, B.D., Tiranov, P.P., Lebed, I.G., Kadantseva, Y.A., 1983. Technical lignins as promising ingredients for sole rubbers. Izv. Vyssh. Uchebn. Zaved., Tekhnol. Legk. Prom-sti. 26, 53.
Savel'eva, M.B., Shevtsova, K.V., Shelkovnikova, L.A., Kercha, Y.Y., Onishchenko, Z.V., 1988. Effect of a binary system of lignin-based
235
modifiers on the physicomechanical properties of vulcanizates. Kompoz. Polim. Mater. 38, 40.
Scandola, M., Pizzoli, M., Ceccorulli, G., 1993. Thermal properties of polymer blends based on biodegradable bacterial polyesters. Calorim. Anal. Therm. 24, 433-6.
Schneider, H.A., 1988. The Gordon-Taylor equation. Additivity and interaction in compatible polymer blends. Die Makromolekulare Chemie 189, 1941-1955.
Scott, G., 2002, Degradable polymers, principles and application, In, Kluwer academic publisher, Dordrecht.
Segal, L., Creely, J.J., Martin, A.E., Conrad, C.M., 1959. An empirical method for estimating the degree of crystallinity of native cellulose using the X-ray diffractometer. Text. Res. J. 29, 786.
Sestauber, K., Fiala, V., Maca, K., Valenta, D., 1988. Lignosulfonate additive for improved workability of concrete mixtures. CS 249 038.
Shafizadeh, F., 1968. Pyrolysis and combustion of cellulosic materials. Adv. Carbon Chem. 23, 419.
Shperber, R.E., Shperber, E.R., Shperber, F.R., Shperber, I.R., Shperber, R.S., Shperber, D.R., 2004. Freezing-resistant concrete mix. RU 2 233 814.
Sierra, R., Smith, A., Granda, C., Holtzapple, M.T., 2008. Producing fuels and chemicals from lignocellulosic biomass. Chem. Eng. Prog. 104, S10.
Silva, M.F., da Silva, C.A., Fogo, F.C., Pineda, E.A.G., Hechenleitner, A.A.W., 2005. Thermal and FTIR study of polyvinylpyrrolidone/lignin blends. J. Therm. Anal. and Calorim. 79, 367-370.
Sixun, Z., Qipeng, G., Chi-Ming, C., 2003. Epoxy resin/poly(ɛ-caprolactone) blends cured with 2,2-bis[4-(4-aminophenoxy)phenyl]propane. II. Studies by Fourier transform infrared and carbon-13 cross-polarization/magic-angle spinning nuclear magnetic resonance spectroscopy. J. Polym. Sci., Part B: Polym. Phys. 41, 1099-1111.
Sjoblom, J., Gundersen, S.A., Myrvold, B.O., 2000. Lignine composition as stabilizer in water based emulsions. WO 2000 050 164.
Sjöström, E., 1993. Wood chemistry–fundamentals and applications, Academic Press, San Diego.
Sluiter, A., Hames, B., Ruiz, R., Scarlata, C., Sluiter, J., Templeton, D., 2008a, Determination of ash in biomass:Laboratory Analytical Procedure (LAP), In.
Sluiter, A., Hames, B., Ruiz, R.S., C. , Sluiter, J., Templeton, D., Crocker, D., 2008b, Determination of Structural Carbohydrates and Lignin in Biomass Laboratory Analytical Procedure (LAP), In.
Smook, G.A., 1934. Handbook for pulp & paper technologists, Angus Wilde Publications, Vancouver.
Smook, G.A., 2002. Handbook for Pulp and Paper Technologies, 3rd ed. Angus Wilde Publications, Inc., Vancouver, B.C.
Souza, B.S., Moreira, A.P.D., Teixeira, A.M.R.F., 2009. TG-FTIR coupling to monitor the pyrolysis products from agricultural residues. J. Therm. Anal. Calorim. 97, 673.
Spear, S.K., Holbrey, J.D., Roger, R.D., 2002. J. Am. Chem. Soc. 124, 4874. Spraul, B.K., Brady, R.L., Allen, A.J., 2008. Adhesive composition of low
molecular weight polyaminopolyamide-epichlorohydrin resin and protein. WO 2008 024 444.
236
Stewart, D., 2008. Lignin as a base material for materials applications: Chemistry, application and economics. . Ind. Crop. Prod. 27, 202.
Sticklen, M.B., 2008, Mariam Sticklen's Home Page, In: Biofuel & Biopharmaceutical Crop Genetic Engineering Lab, Dept. of Crop and Soil science, East Lansing.
Sticklen, M.B., 2008. Use of RNA interference to limit lignin biosynthesis in maize and increase cellulose accumulation for use in ethanol biofuel production. U.S. 2008 213 871.
Sukai, K., Kagawa, I., 1958. The crystal structure of cellulose triacetate and some corresponding properties. Kogyo Kagaku Zasshi 61, 752.
Sun, L., Aklonis, J.J., Salovey, R., 1993. Model filled polymers. XIV: Effect of modifications of filler composition on rheology. Polym. Eng. Sci. 33, 1308-1319.
Sutyagina, S.E., Glukhov, V.I., Zoldners, J., 1987. Effect of wood moisture content on the graft polymerization of methyl methacrylate onto the aromatic and carbohydrate fractions of wood. Khim. Drev. 97.
Swatloski, R.P., Rogers, D., Holbery, J.D., 2003. WO 2003 029 329. Sykes, K., 2001, Plastics you could eat - recycling, In: First science.com. Szabo, P., Varhegyi, G., Till, F., Faix, O., 1996. Thermogravimetric/mass
spectrometric characterisation of two energy crops, Arundo donax and Miscanthus sinensis. J. Anal. Appl. Pyrol. 36, 179.
Szalay, P.J., Johnson, C.A., 1969. Improving heat stability of vinyl chloride polymers. U.S. 3 484 397.
Tan, S.S.Y., MacFarlane, D.R., Upfal, J., Edye, L.A., Doherty, W.O.S., Patti, A.F., Scott, J.L., 2009. Extraction of lignin from lignocellulose at atmospheric pressure using alkylbenzenesulfonate ionic liquid. Green Chem.
Tanczos, I., Pokol, G.J., Borsa, J., Toth, T., Schmidt, H., 2003. The effect of tetramethylammonium hydroxide in comparison with the effect of sodium hydroxide on the slow pyrolysis of cellulose. J. Anal. Appl. Pyrol. 68−69, 172.
Teramoto, Y., Lee, S.-H., Endo, T., 2009. Phase structure and mechanical property of blends of organosolv lignin alkyl esters with poly(ε-caprolactone). Polym. J. (Tokyo, Jpn.) 41, 219.
Tertyshnaya, Y.V., Shibryaeva, L.S., 2006. Use of differential scanning calorimetry to study oxidation of polymer mixtures. Plast. Massy 46-48.
Tinnemans, A.H.A., Greidanus, P.J., 1984, Chemically modified lignin for the use in polymer blends, In: Comm. Eur. Communities, Inst. Appl. Chem., Utrecht, Neth., pp. 492-494.
Toh, K., Nakano, S., Yokoyama, H., Ebe, K., Gotoh, K., Noda, H., 2005. Anti-deterioration effect of lignin as an ultraviolet absorbent in polypropylene and polyethylene. Polym. J. (Tokyo, Jpn.) 37, 633.
Tomasi, G., Scandola, M., 1995. Blends of bacterial poly(3-hydroxybutyrate) with cellulose acetate butyrate in activated sludge. Plast. Eng. (N. Y.) 29, 79-89.
Tomita, B., 1998. New resin system from lignin. Science and Technology of Polymers and Advanced Materials: Emerging Technologies and Business Opportunities, [Proceedings of the International Conference on Frontiers of Polymers and Advanced Materials], 4th, Cairo, Jan. 747.
237
Toriz, G., Denes, F., Ramos, J., Young, R.A., 2002. Lignin-polypropylene composites part 3. Composites from plasma treated lignin and polypropylene. Int. Conf. Woodfiber-Plast. Compos., 6th 207.
Ugartondo, V., Mitjans, M., Vinardell, M.P., 2008. Comparative antioxidant and cytotoxic effects of lignins from different sources. Bioresour. Technol. 99, 6683.
Uraki, Y., Hashida, K., Sano, Y., 1997. Self-assembly of pulp derivatives as amphiphilic compounds. Preparation of amphiphilic compound from acetic acid pulp and its properties as an inclusion compound. Holzforschung 51, 91.
Uyama, H., Motoki, K., Yin, Y., Funaoka, M., 2008. Plant-derived lignophenol-poly(lactic acid) complex for modifier of poly(lactic acid). JP 2008 274 068.
Vanderlaan, M.N., Thring, R.W., 1998. Polyurethanes from Alcell® lignin fractions obtained by sequential solvent extraction. Biomass Bioenergy 14, 525-531.
Vasile, C., Iwanczuk, A., Frackoviak, S., Cazacu, G., Constantinescu, G., Kozlowski, M., 2006. Modified lignin/polyethylene blends. Cellul. Chem. Technol. 40, 345.
Vaughan, C.W., Adamsky, F.A., Richardson, P.F., 1998. A new approach to wet end drainage/retention/formation technology and its improvement of paper machine production rates and runability. Wochenbl. Papierfabr. 126, 458,462,466,470.
Vazquez, G., Rodriguez-Bona, C., Freire, S., Gonzalez-Alvarez, J., Antorrena, G., 1999. Acetosolv pine lignin as copolymer in resins for manufacture of exterior grade plywoods. . Bioresour. Technol. 70, 209.
Verhoogt, H., Ramsay, B.A., Favis, B.D., 1994. Polymer blends containing poly(3-hydroxyalkanoate)s. Polymer 35, 5155-5169.
Viswanathan, S., Dadmun, M.D., 2002. Guidelines To Creating a True Molecular Composite: Inducing Miscibility in Blends by Optimizing Intermolecular Hydrogen Bonding. Macromolecules 35, 5049-5060.
Wallberg, O., Jönsson, A.S., Wimmerstedt, R., 2003. Fractionation and concentration of kraft black liquor lignin with ultrafiltration. Desalination 154, 187-199.
Wang, D., Luo, D., Jia, L., 1992. Microstructure and properties of high lignin-formaldehyde resin filled NBR-26 vulcanizate. Hecheng Xiangjiao Gongye 15, 12.
Wang, H., de Vries Frits, P., Jin, Y., 2009. A win-win technique of stabilizing sand dune and purifying paper mill black-liquor. Journal of Environmental Sciences 21, 488-493.
Wang, H., Easteal, A., Edmonds, N., 2008. Prevulcanized natural rubber latex/modified lignin dispersion for water vapour barrier coatings on paperboard packaging. Adv. Mater. Res. (Zuerich, Switz.) 47-50, 93.
Wang, J., Manley, R.S.J., Feldman, D., 1992. Synthetic polymer-lignin copolymers and blends. Prog. Polym. Sci. 17, 611.
Wang, Y.Y., Peng, W.J., Chai, L.Y., Peng, B., Min, X.B., He, D.W., 2006. Preparation of adhesive for bamboo plywood using concentrated papermaking black liquor directly. J. Cent. South Univ. Technol. (Engl. Ed.) 13, 53.
238
Watado, H., Fujieda, S., Fukaya, T., Motomiya, A., Kondo, A., Oyazato, Y., 2009. Lignin-based adsorbents and manufacture thereof. JP 2009 034 634.
Wehner, A., Fenyvesi, G., Muska, C.F., Desalvo, J.W., Joerger, M., Miller, R., Palefsky, I.A., Poladi, R.H.P., 2007. Biodegradable compositions comprising renewably-based, biodegradable 1,3-propanediol. WO 2007 095 255.
Wei, M., Fan, L., Huang, J., Chen, Y., 2006. Role of star-like hydroxylpropyl lignin in soy-protein plastics. . Macromol. Mater. Eng. 291, 524.
Weihua, K., He, Y., Asakawa, N., Inoue, Y., 2004. Effect of lignin particles as a nucleating agent on crystallization of poly(3-hydroxybutyrate). J. Appl. Polymer Sci. 94, 2466.
Williams, P.T., Horn, P.A., 1994. The role of metal salts in the pyrolysis of biomass. Renewable Energy 4, 1.
Winowiski, T.S., Zajakowski, V.L., 1998. Animal feed incorporating reactive magnesium oxide. EP 834 258.
Withey, R.E., Hay, J.N., 1999. The effect of seeding on the crystallisation of poly(hydroxybutyrate), and co-poly(hydroxybutyrate-co-valerate). Polymer 40, 5147-5152.
Wong, A., 1980. Sulfite pulping: a review of its history and current technology. Pulp Pap. 54, 74.
Woolnough, C.A., Yee, L.H., Charlton, T., Foster, L.J.R., 2010. Environmental degradation and biofouling of ‘green’ plastics including short and medium chain length polyhydroxyalkanoates. Polym. Int. 59, 658-667.
Wu, C.S., 2006. Assessing biodegradability and mechanical, thermal, and morphological properties of an acrylic acid-modified poly(3-hydroxybutyric acid)/wood flours biocomposite. Journal of Applied Polymer Science 102, 3565-3574.
Wu, R.L., Wang, X.L., Li, F., Li, H.Z., Wang, Y.Z., 2009. Green composite films prepared from cellulose, starch and lignin in room-temperature ionic liquid. Bioresour. Technol. 100, 2569-2574.
Xing, P., Dong, L., An, Y., Feng, Z., Avella, M., Martuscelli, E., 1997. Miscibility and crystallization of poly(β-hydroxybutyrate) and poly(p-vinylphenol) blends. Macromolecules 30, 2726-2733.
Xu, Y., Zeng, S.-J., Zhou, H.-F., Shen, Q., 2007. Blending and miscibility of poly(butylene terephthalate) with lignin. Xianweisu Kexue Yu Jishu 15, 36, 44.
Yang, S., Liu, Q., 2002. Effect of lignin modification on synthetic properties. Emerging Technol. Pulping Papermaking, Proc. Int. Symp., 2nd 782.
Yano, S., Murakami, K., Sawayama, S., Imou, K., Yokoyama, S., 2009. Ethanol production potential from oil palm empty fruit bunches in southeast asian countries considering xylose utilization. J. Jpn. Inst. Energy 88, 923-926.
Yao, F., Wu, Q., Lei, Y., Guo, W., Xu, Y., 2008. Thermal decomposition kinetics of natural fibers: Activation energy with dynamic thermogravimetric analysis. Polym. Degrad. Stab. 93, 90-98.
Yao, F., Wu, Q., Lei, Y., Guo, W., Xu, Y., 2009. Thermal decomposition kinetics of natural fibers: Activation energy with dynamic thermogravimetric analysis. Polym. Degrad. Stab. 93, 90.
Yao, K., 2008. Recyclable resin composition based on polylactic acid and lignophenols for molded parts of business equipment. U.S. 2008 048 365.
239
Yong, H., Naoki, A., Yoshio, I., 2001. Blend of Poly(ɛ-caprolactone) and 4,4'-Thiodiphenol: Hydrogen Bond Formation and Some Solid Properties. Macromol. Chem. Phys. 202, 1035-1043.
Yoshie, N., Azuma, Y., Sakurai, M., Inoue, Y., 1995. Crystallization and compatibility of poly(vinyl alcohol)/poly(3-hydroxybutyrate) blends: influence of blend composition and tacticity of poly(vinyl alcohol). J. Appl. Polym. Sci. 56, 17-24.
Zhang, L., Deng, X., Zhao, S., Huang, Z., 1997. Biodegradable polymer blends of poly(3-hydroxybutyrate) and poly(DL-lactide)-co-polyethylene glycol. J. Appl. Polym. Sci. 65, 1849-1856.
Zhang, L., Xiong, C., Deng, X., 1996. Miscibility, crystallization and morphology of poly(β-hydroxybutyrate)/poly(d,l-lactide) blends. Polymer 37, 235-241.
Zhao, L., Kai, W., He, Y., Zhu, B., Inoue, Y., 2005. Effect of aging on fractional crystallization of poly(ethylene oxide) component in poly(ethylene oxide)/poly(3-hydroxybutyrate) blends. J. Polym. Sci., Part B: Polym. Phys. 43, 2665-2676.
Zheng, S., Mi, Y., 2003. Miscibility and intermolecular specific interactions in blends of poly(hydroxyether of bisphenol A) and poly(4-vinyl pyridine). Polymer 44, 1067-1074.
Zhong, Z., Sun, X.S., 2001. Properties of soy protein isolate/polycaprolactone blends compatibilized by methylene diphenyl diisocyanate. Polymer 42, 6961.
Zhou, J., Luo, X., 2007. Preparation of lignin/LDPE/EVA composite foam. Huagong Xuebao (Chin. Ed.) 58, 1834.
Zhuang, J.M., Walsh, T., 2003. Application of lignosulfonates in treatment of acidic rock drainage. Hydrometall. 2003, Proc. Int. Symp., 5th 2, 1873.
Zschiegner, H.J., 1999. Use of lignins and lignin derivatives as UV protectants for biological insecticides. DE 19 750 482.