progress on cellulose nanofiber - filled thermoplastic...
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Progress on cellulose nanofiber-filled thermoplastic composites
Douglas J. Gardner, Yousoo Han, Alper Kiziltas, and Yucheng Peng
Session 5: The role of nanotechnology in green materials and sustainable
construction.
Overview
• Why cellulose nanofiber (CNF)-filled composites?
• UMaine’s cellulose nanocomposites research program
• Engineering thermoplastics• Thermoplastic starch carrier for CNF• Drying CNF without agglomeration• Challenges
Nanotech is 3rd Industrial RevolutionUS Gov. R&D in Nanotech = $1.5 billion/yrSurface of Nanos in 1 raindrop = 1 football fieldCellulose: Maine’s Niche to Compete in Nanotech
Stone Age ……. Bronze Age ………. Iron Age …….......... Nano Age?
“From the Sawmill to the Nanomill?”
Renewable resource and broad availability No impact of environmental pollution due to biodegradability No toxic by-products after combustion Low machine wear in processing Low density and high strength compared with inorganic fillers
Why cellulose nanofibrils?
Lignocellulose is a Renewable Resource Abundant in Maine
A Wealth of Cellulose Nanofibril (CNF) Architectures are Possible
Applications Range from Nano to Macro Components
bacterial cellulose nanofibrillated cellulose electrospun cellulose cellulose whiskers
Research Theme #1Synthesis of Nano-fibers
from Lignocellulose Sources
Objective: Produce inexpensive lignocellulosic-
based nanofibers with known and consistent properties.
Research Theme #2Functionalization of
Lignocellulose
Objective: Achieve precise control of nanofiber surface and interfacial chemistry to
obtain desired adhesion and dispersion.
Research Theme #3Materials
Characterization
Objective: Characterize cellulose nanofibril-derived
materials and determine structure/property relationships from nano- to macro- scales.
ResearchTheme #4Modeling and Visualization
Objective: Develop multi-scale micro- and nano-
simulation and visualization techniques to predict materials
performance.
Research Theme #5Structural Composites
Objective: Develop pilot-scale processes to utilize nanoscale lignocellulose derived fibers
and CNFs in structural composites.
Research Theme #6Smart Materials and
Devices
Objective: Develop nanoscale devices, structures, and films
for nanoelectronics, tissue engineering, sensing,
actuation, and separation membrane applications.
Nanoscale Imaging & Characterization Laboratory - LASST
Processing Lab for Cellulose Nanocomposites in Structural/
Off Shore Wind Applications - AEWC
Cellulose Nanofiber Production and Functionalization Laboratory - FBRI
Physical Infrastructure for Cellulose Nanotechnology
Because of the hydrophilic nature of cellulose nanofibrils many studies have focused on nanocomposites based on hydrophilic polymer matrices.
There have been very few research studies focusing on CNF in hydrophobic polymers such as PE and PP.
Challenges using CNF in Hydrophobic Polymers
Siro and Plackett, Cellulose 17, 459 (2010)
Why engineering thermoplastics (ETP)? ETP defined as materials which can be used structurally, typically
replacing metals, wood, glass, or ceramics. These high-performance polymers provide innovative solutions that
save weight and reduce costs.
Thermal stability The processing temperature of wood/natural fiber composites are
typically restricted to around 200 C. The earliest experiments to reinforce engineering thermoplastics
exhibited severe discoloration and pronounced pyrolyticdegradation.
Time (min)0 10 20 30 40 50 60 70
Mas
s C
han
ge
(%)
80
85
90
95
100
105
70 um WF50 um MCCNeat Nylon
Mas
s C
han
ge
(%)
Hea
t F
low
En
do
Up
(m
W)
Temperature (°C)0 100 200 300 400 500
0
20
40
60
80
100
60 um W.F50 um MCCDSC of PET-PTTDSC of Nylon 6
MCC decomposes
Wood decomposes
Isothermal TGA @ 250 °C
Methods-Production
ETPsMCC
Lubricant
High Speed Mixer
Melt BlendBrabender
Dry Ground Mixture
Injection Molding
ASTM Test Samples
nanofibrillated cellulose
Comparison of ETPC’s and Commodity Plastics
Mechanical Properties Melting Temperature
Temperature (°C)0 50 100 150 200 250
LDPE
HDPE
PP
PVC
PA
PET-PTT
Wood Degradation
Stiffness Enhancement of MCC-Filled ETPC’s Using Nanoclay
To investigate the reinforcement effects of Nanoclay on the stiffness of20% MCC- filled engineering thermoplastic composites.
To also investigate the effect of Nanoclay on the MCC/Nanoclay/PA 6composites thermal properties.
Thermoplastic Starch The literature is confusing and describes thermoplastic,
destructurized, gelatinized and plasticized starch. Structure is overcome with a combination of plasticizer,
heat and pressure to process the starch. Plasticization is the easiest and cheapest way to put
technological materials in a processable state.
Our ApproachBase Polymer
(Hydrophobic Matrix)Nanoscale Additive
(Filler, Dispersed Phase NC)Carrier System
(Thermoplastic Starch)
Hydrophobic Thermoplastic Compositeswith better dispersion and improved properties
Native Starch
WaterGlycerol
HeatPressure
Thermoplastic Starch (TPS)
NCHydrophilic
NC filled TPS
PolymerHydrophobic
Dispersed NC in Hydrophobic Matrix
NC NC in Hydrophobic Matrix Conventional Composite
Tensile Properties of the Composites
18
TPS and NCTPS filled PP composites showed comparable or lowertensile strength and modulus compared to control samples.
Group NamePP PP+S PP-TPS 5NCTPS 10NCTPS 15NCTPS
Tens
ile S
tres
s (M
Pa)
18
19
20
21
22
2304 Weeks8 Weeks
Group NamePP PP+S PP-TPS 5NCTPS 10NCTPS 15NCTPS
Ten
sile
Mo
du
lus
(GP
a)1.0
1.1
1.2
1.3
1.4
04 Week8 Week
Flexural Properties of the Composites
19
TPS and NCTPS filled PP composites showed comparable or lower flexuralstrength and modulus compared to control samples like tensile properties.
Group NamePP PP+S PP-TPS 5NCTPS 10NCTPS 15NCTPS
Flex
ural
Str
engt
h (M
Pa)
20
22
24
26
28
30
32
3404 Weeks8 Weeks
Group NamePP PP+S PP-TPS 5NCTPS 10NCTPS 15NCTPS
Fle
xura
l Mo
du
lus
(GP
a)0.8
0.9
1.0
1.1
1.204 Weeks8 Weeks
TGA and DTGA of Composites
20
TGA and DTGA results showed that thermal stability of compositesdecreased marginally with the addition of TPS and NCTPS.
Time(sec)0 1000 2000 3000 4000
Mass C
han
ge (
%)
0
20
40
60
80
100
TPS at 150°CTPS at 190°CTPS at 230°CTPS at 270°CS at 150°CS at 190°CS at 230°CS at 270°
SEM Micrographs of TPS-Based Comp.
The PP matrix was inert, we had no TPS–matrix interactions. From SEMobservation, we can visualize that the fibrils were embedded in TPS. This is due tostrong interactions between the cellulose fibrils and the plasticized starch matrix.
PP-T
PS
PP-5
NC
TPS
PP-1
0NC
TPS
PP-1
5NC
TPS
Challenges for scale-up of producing CNF• Major issue : Processing by classical
method (extrusion, injection) using cellulose micro-nanofibrils in dry state without any chemical modification.
• Scaling-up of homogenization technologies.
• Energy and enzymes consumption.• Reduction of clogging problems.• Controlling cellulose micro-nanofibrils
agglomeration.• Reduction of production costs.
Cellulose and Hydrogen Bonding
(Klemm et al. 1998)
(Wegner 2009)
Aggregation1) Inter and intra-molecular
hydrogen bonds2) van der Waals forces
Challenges• Aqueous nature of cellulose nanofibrils
because of the rich hydroxyl groups on the surface– Agglomeration
– Absorption of atmospheric moisture
– Poor compatibility between polar cellulose nanofibril and apolarpolymer matrix
Different morphologies of nanocellulose by different drying processes
Something like this?
Ideal dry form of cellulose nanofibrils for polymer processing with thermoplastics
Planned Surface Modification
• Methods• Physical
• Plasma
• Chemical• Esterification• Coupling agent treatment
(Selli et al. 2001)
Silane treated wood fibers for reinforcing fillers in thermoplastic composites
Silane 1:N-[3-(trimethoxysilyl)propyl]butylamine
Experimental ConceptSurface of cellulose or wood fiber treated with organic silanes which have two or more domains for fillers and matrices.
Silane 2:(3-Chloropropyl)triethoxysilane+ Cellulose
Experimental Results
Polyethylene
Flexural MOR, psi
control silane1 silane2 control silane1 silane2
Flexural MOE, psi
control silane1 silane2
Tensile strength, psi
control silane1 silane2
Tensile modulus, psi
control silane1 silane2
CTE, 10-2
control silane1 silane2
Water weight percent gain, %
Dispersion of CNF in compositesCellulose nanofibrils were dispersed in the wood-inorganic composite through a sodium silicate solution.
Fracture surface of wood-inorganic composite (5 wt. % of cellulose nanofibrils)
Conclusions• Thermoplastic-CNF composites with enhanced material
properties are possible.• Ongoing challenges for scale-up of utilizing cellulose
nanofibrils in hydrophobic thermoplastics will be the need for obtaining large quantities of CNF in the dry state.
• For the process of producing nano-fibrillated cellulose on the commercial scale, scale up of adequate homogenization technologies is still needed.
• Control of CNF agglomeration and scalable drying technologies is also a big challenge.
• Surface treatment of CNF via physical and/or chemical modification methods will be important to tailor CNF surfaces for application in specific polymer matrices.
Acknowledgements: The authors thank the Army Corp of Engineers ERDC, USDAWood Utilization Research Special Grant, and McIntire Stennis for funding support.