toward thermoplastic lignin polymers; synthesis &...
TRANSCRIPT
H. Sadeghifar, C. Cui, S. Sen
Dimitris S. Argyropoulos*
Departments of Chemistry and Forest Biomaterials North Carolina State University , Raleigh , NC USA
& *Advanced Materials Research Center of Excellence,
King Abdulaziz University, Jeddah, Saudi Arabia. Cost Action FP 0901, “Biorfinery Analytics”,
Turku, Finland, September 17-18, 2013.
Toward Thermoplastic Lignin Polymers; Synthesis & Analysis
Objective
To describe our approach aimed at creating heat stable technical lignin melts
& Aimed at Thermoplastics, Precursor to carbon Fibers & Engineering Heat Stable Polymers
The concerted use of a variety of analytical tools
is indispensable in such endeavors
Fundamental Science aimed at Creating Thermoplastic Lignin Melts
Heat Stable Polyarylene Ether Sulfone -Kraft Lignin Co-Polymers
Defining the Science & a Novel Approach aimed at Creating Carbon Fibers from Lignin Melts
Fundamental Science aimed at Creating Thermoplastic Lignin Melts
Softwood kraft lignin is highly susceptible to thermally induced
reactions that cause its molecular characteristics to be severely
altered. These events seriously interfere and prevent such materials
from being considered as candidates for thermoplastic applications.
Kraft Lignin Structure In Bad Need for A New Model
Marton, J. 1971.
Effect of Heating on the Molecular Weight Distribution
of Underivatized Kraft Lignin
Cui, C., et al. “Toward Thermoplastic Lignin Polymers; Part II: " BioResources 8(1), 864-886, (2013).
Starting Softwood Kraft Lignin “Indulin” Molecular Weight : Mw = 8000 (g/mol) Mn = 2000 ( g/mol) ( Mw/Mn = 4 ) Total phenolic-OH = 3.85 mmol/ g Total Aliphatic-OH = 2.4 mmol/g Tg : 150-160°C .
Kawamoto, et al. J. Wood Sci. 2007, 53(2) &53(3)&27(2); J. Anal. Appl. Pyrolysis 2008, 81 (1), 88-94. Holzforschung 2008, 62 (1), 50. Ohashi, et al.. Org. Biomol.. Chem. 2011, 9 (7), 2481-2491
Kawamoto,et al, J. Wood Chem. Technol. 2007, 27 (2), 113-120.; Holzforschung 2008, 62 (1), 50
How does the Phenolic OH & its Derivatives Define the Thermal
Reactivity of Kraft Lignin ?
Effect of Heating Kraft Lignin & Derivatives 20 0C above Tg on Molecular Weight
Cui, C., et al. “Toward Thermoplastic Lignin Polymers; Part II: " BioResources 8(1), 864-886, (2013).
Since methylation of the Phenolic OH with Dimethyl Sulfate showed promising thermal stability…
• Is this stability permanent ? • Can the material withstand heating &
Cooling cycles ? • How does the Molecular Weight
Distribution of the material is affected by repeated Heated & Cooling Cycles?
• Polymer Processing Simulating Conditions (Measure Melt Torque, f(time) with a Lab Mini-extruder).
2nd Heating
3rd Heating
Minute Changes in the Mol. Wt Distributions are Indicative of the Sought Chemically Stable Melt Characteristics
Cui, C., et al. “Toward Thermoplastic Lignin Polymers; Part II: " BioResources 8(1), 864-886, (2013).
3500
3700
3900
4100
4300
4500
4700
4900
5100
1 2 3 4 5 6 7 8 9 10
Exrtrude
r force, N
Time, min.
Comparison of Torque ( N ) as a function of melt mixing time for Blends of PP with Non Derivatized (Un-Methylated) and Fully
Methylated Kraft Lignin 25% lignin
Methylated
Un-methylated
The melt stability of methylated Kraft Lignin has been verified using melt torque measurements
There is no melt stability for non-derivatized Kraft Lignin due to the onset of crosslinking reactions
A multitude of inter & intra molecular thermal events in Kraft lignin may be avoided by the selective and complete methylation of its phenolic OH groups. Thus preventing the phenoxy radicals & QM’s from forming and reacting .
Toward Carbon Fibers from Technical Lignin
Defining the Science & a Novel Approach aimed at Creating Carbon Fibers from Lignin Melts
S. Sen, et al. “Toward Thermoplastic Lignin Polymers; Part III: " Biomacromolecules (2013).
Since derivatization of the Phenolic OH allowed the modulation of the thermal stability…
Eventual aim: Carbon Fibers from Lignin
• Can one modulate thermal crosslinking? • Can one regulate the rate of Mol.
Weight Increase? • By introducing activated (thermally
labile) centers how does the Molecular Weight Distribution of the material is affected ?
Towards Reactive Extrusion Lignins
Kraft Lignin Chain Extension Chemistry via Propargylation, Oxidative Coupling & Claisen
Rearrangement
Biomacromolecules : http://dx.doi.org/10.1021/bm4010172,
Propargylation of lignin
Biomacromolecules : http://dx.doi.org/10.1021/bm4010172,
Initial Characterizations of Propargylated Lignin
60
80
100
120
140
1,000 2,000 3,000 4,000
98%
89%
68%
42%
22%
0% Cm-‐1
Intensity
Alkyne C-H stretching
Terminal alkyne CC stretching
NMR Spectroscopy
Alkyne proton
Alkyne carbon
1H
13C
FT-IR Spectroscopy
% of propargylation
20
Non-Condensed Phenolic -OH
Condensed Phenolic -OH
Aliphatic -OH
Reactivity of Lignin Hydroxyl Groups Towards Propargylation
• Initial reaction rate of the condensed phenolic –OHs are same as non-condensed phenolic –OHs
• However the rate of substitution slows down in non-condensed phenolic -OHs in the latter part
• Aliphatic –OHs remain unaffected during propargylation reaction
0.00
20.00
40.00
60.00
80.00
100.00
120.00
0.00 0.50 1.00 1.50 2.00 2.50
% of -‐OH remaining
Molar ratio of propargyl bromide to total phenolic -‐OH
0.00
20.00
40.00
60.00
80.00
100.00
120.00
0.00 0.50 1.00 1.50 2.00 2.50
% of -‐OH remaining
Molar ratio of propargyl bromide to total phenolic -‐OH
0.00
20.00
40.00
60.00
80.00
100.00
120.00
0.00 0.50 1.00 1.50 2.00 2.50
% of -‐OH remaining
Molar ratio of propargyl bromide to total phenolic -‐OH
Biomacromolecules : http://dx.doi.org/10.1021/bm4010172,
ASKL Starting Material
25% Propargylated
48% Propargylated
72% Propargylated
92% Propargylated
98% Propargylated
Exo
Thermal Properties of the Propargylated Lignin
• The thermal stability increases significantly after propargylation
• The thermal stability keeps on improving marginally with the increase of degree of propargylation
• DSC traces show an exotherm with an onset and a maximum around 150 °C and 215 °C respectively
22
40
50
60
70
80
90
100
100 200 300 400 500 600
Wt %
Temperature ( C)
40
50
60
70
80
90
100
100 200 300 400 500 600
Wt %
Temperature ( C)
40
50
60
70
80
90
100
100 200 300 400 500 600
Wt %
Temperature (°C)
98%89%
68%43%22%
0
1
2
3
4
5
0 100 200 300
Heat flow
Temperature °C)
0%
Degree of Propargylation
DSC Traces
TGA Traces
The Versatility of the Installed Propargyl Groups Toward Chain Extension Chemistry
Biomacromolecules : http://dx.doi.org/10.1021/bm4010172,
Hydride shi, Benzopyran
Claisen Rearrangement
Thermal PolymerizaMon
Thermally Induced Polymerization of the Propargylated Lignin
Biomacromolecules : http://dx.doi.org/10.1021/bm4010172,
Bulk Thermal Polymerization of the Propargylated Lignin
• About 40 mg of the propargylated softwood kraft lignin samples were heated within the chamber of a thermogravimatric analysis apparatus (TGA) for predetermined times at predetermined (to optimize the molecular weight) temperatures under a nitrogen atmosphere
Temperature (°C)
Time (min)
Mn (g/mol)
Mw (g/mol)
PDI
Before thermal polymerization
0 0 1,500 2,160 1.44
Sample 1 150 10 2,100 5,200 2.53
Sample2 150 60 2,300 10,400 4.49
Sample 3 170 10 2,330 11,400 4.88
Sample 4 170 20 Gelation Confiden5al NCSU Informa5on to Solvay
KL 20% methylated 80% activated 150 °C, 10 min
KL 20% methylated
80% activated 150 °C, 60 min
KL 20% methylated 80% activated 150 °C, 10 min
KL 20% methylated 80% activated 170 °C, 10 min
KL 20% methylated
80% activated 150 °C, 60 min
KL 20% methylated 80% activated 150 °C, 10 min
The molecular weight distribution gradually increases with increasing temperature and time of heating
1, 2 3, 4 O
OOCH3
OCH3 L
L
1
2
3 4
Before bulk thermal PolymerizaMon reacMon
AOer bulk thermal PolymerizaMon reacMon
Biomacromolecules : http://dx.doi.org/10.1021/bm4010172,
Aliphatic –OH (mmol/g)
Total phenolic –OH (mmol/g)
Carboxylic –OH (mmol/g)
25% methylated 75% propargylated lignin 1.44 0.36 0.43
25% methylated 75% propargylated lignin after heating at 150 oC for 60 min
1.22 0.40 0.32
Stability of Aliphatic and Phenolic –OHs of Lignin after Thermal Polymerization
25% methylated 75% propargylated lignin
25% methylated 75% propargylated lignin
after heating at 150 0C
for 60 min
Confiden5al NCSU Informa5on to Solvay
Diacetylene
Terminal alkyne
13C NMR Spectrum
• 13C NMR spectrum of the polymer after the oxidative coupling reaction. The peaks of dialkyne carbons can be clearly seen between 68 to 72 ppm.
• Peaks between 85 to 91 ppm are due to unreacted terminal alkynes
Characterizations of the Coupled Propargylated Lignin
Lignin sample used for coupling reaction
Temperature (°C)
Time (h)
Mn g/mol
Mw g/mol
PDI
Coupling 0 98% propargylated 25 1 Gelation Before coupling 25% methylation 75%
propargylation 0 0 1,500 2,140 1.42
Coupling 1 25% methylation 75% propargylation
25 24 2,100 3,600 1.71
Coupling 2 25% methylation 75% propargylation
60 24 2,300 10,000 4.68
Coupling 3 25% methylation 75% propargylation
80 6 2,000 11,000 5.77
Coupling 4 25% methylation 75% propargylation
80 24 Gelation
Oxidative Coupling of the Propargylated Lignin
Oxidative coupling reaction was conducted at different temperature and for different time period (as shown in the following table)to optimize the molecular weight distribution
Biomacromolecules : http://dx.doi.org/10.1021/bm4010172,
Before Coupling
Coupling 1
Coupling 2
Coupling 3
Molecular Weight Distributions
• With the increase in time and temperatur of the reaction medium the molecular weight distribution curves shifts towards the higher molecular weight direction showing progression in the polymerization reaction
0
0.2
0.4
0.6
0.8
1
1.00E+001.00E+031.00E+06
Absorption (a.u.)
Weight average molecular weight distribution (Mw) g/mol
0
0.2
0.4
0.6
0.8
1
1.00E+001.00E+031.00E+06
Absorption (a.u.)
Weight average molecular weight distribution (Mw) g/mol
0
0.2
0.4
0.6
0.8
1
1.00E+001.00E+031.00E+06
Absorption (a.u.)
Weight average molecular weight distribution (Mw) g/mol
0
0.2
0.4
0.6
0.8
1
1.00E+001.00E+031.00E+06
Absorption (a.u.)
Weight average molecular weight distribution (Mw) g/mol
Biomacromolecules : http://dx.doi.org/10.1021/bm4010172,
Thermal Properties after Oxidative Coupling Reaction
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100 200 300 400 500 600
Wt %
Temperature (°C)
0% Propargylated
25% Propargylated
48% Propargylated
92% Propargylated
72% Propargylated
98% Propargylated
(A)
Biomacromolecules : http://dx.doi.org/10.1021/bm4010172,
Toward Heat Stable Poly (Arylene Ether)
Sulfone-Lignin Heat Stable Copolymers
Why Poly (Arylene Ether Sulfones) • Ease of preparation, • Ease of functionalization, • Thermal & chemical stability • Relatively low cost • Excellent mechanical performance.
ACS Sustainable Chemistry , Argyropoulos et al December 2013
Copolymerization of Kraft Lignin with DifluoroDiphenyl Sulfone (DFDPS)
0
0.2
0.4
0.6
0.8
1
1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06
22% Methylated KL-DFDPS Co-Polymer
Starting Kraft Lignin
71% Methylated KL-DFDPS C0-Polymer
63% Methylated KL-DFDPS C0-Polymer
38% Methylated KL-DFDPS Co-Polymer
Size Exclusion Chromatographic Analyses of Methylated Kraft Lignin DFDPS Co-Polymers .
Typical Step growth polymerization Mol wt. distribution shapes are observed, progressively moving to higher molecular weights
Thermal Degradation Analyses of Methylated Kraft Lignin DFDPS Co-Polymers
DFDPS
71% Methylated KL-‐DFDPS Co-‐Polymer
38% Methylated KL-DFDPS Co-Polymer
35.0
45.0
55.0
65.0
75.0
85.0
95.0
100 150 200 250 300 350 400 450 500 550
KL-DFDPS Co-Polymer
Kraft lignin
Heat stabilities up to 270 0C are observed for these Kraft Lignin DFDPS Copolymers with Tg values at least 100 0C lower
Differential Thermal Scans of Methylated Kraft Lignin DFDPS Co-Polymers .
Tg,172 °C
Tg,170 °C
Tg,166 °C Tg,147 °C
ACS Sustainable Chemistry , Argyropoulos et al December 2013
Glass Transitions Temperature (Tg) as Function of Molecular Weight for a Series of Kraft Lignin –DFDPS Co-Polymers
90
147
166 170
60
80
100
120
140
160
180
1200 3900 5900 6800
Tg , °C
Molecular Weight , g/mol
100 % Lignin
74 % Lignin
69 % Lignin
86% Lignin
ACS Sustainable Chemistry , Argyropoulos et al December 2013
Conclusions
• The selective methylation of the phenolic OH is pivotal in
controlling the thermal stability of technical Lignin
• Molecular Weight Distribution & Melt Extrusion Torque
measurements offer a detailed way of understanding
such thermal events
• Lignin propargylation/methylation offers a versatile new
avenue towards lignin chain extension, reactive extruding
and carbon fiber precursors.
Conclusions
• Thermoplastic Co-polymers of Polyarylene ether Sulfones
with Kraft Lignin have been synthesized displaying :
- Typical Step Growth Mol. Weight Distributions
- Excellent Thermal Stability
- Predictable Mol. vs Wt. Tg Relations
Strategic Decisions • Treating Lignin with respect will pay off • Focus & capitalize on current limitations • Expand into Hardwood & Biorefinery
Lignins • Work with Specific Lignin for specific
high value applications • Work with Industry to bring these to
further development
Acknowledgments • Solvay Specialty Polymers • Domtar Inc. Plymouth NC • King Abdul Aziz University, Centre for
Advanced Materials Research, Jeddah, Saudi Arabia.