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Cellulose- and Chitin-Based Coatings and Films
Carson MeredithProfessor
Chemical & Biomolecular EngineeringGeorgia TechAtlanta, GA
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One Motivation - Packaging
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• 1.3 billion tons of food, 1/3 of the world’s production, is spoiled each year before it gets to a consumer’s table.
• 2012 food/beverage packaging market $276 billion
• 10% is flexible plastic• 27% is rigid plastic• Nearly all of these are petroleum-derived barrier
plastics
www.foodproductiondaily.com
Chem. Soc. Rev. 2011, 40, 5266-5281Chem. Soc. Rev. 2014, 43, 588-610
poly(ethylene terephthalate) (PET) poly(vinylidene chloride))
Motivation
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Other Motivations
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• Composites• Light-weight applications in transportation
sector• Futuris / American Process / Swinburne /
Forest Products Laboratory / Clark Atlanta University Collaboration
• Adhesives• Foams and porous materials
• Lightweighting• Insulative• Battery electrodes
FuturisAmericanProcess
GaTechCAUSwinburneUSDA-FPL
Cellulose in wood and plant structures
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Estimated cellulosenanocrystal
Like carbon fiber,potential for high-strengthbut light-weight
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Chitin
• 2nd most abundant polysaccharide
(1010-1011 tons each year)
• Structure similar to cellulose
• Ability to be functionalized
• Biocompatible
• Remarkable affinity to proteins
• Renewable
Kohr E. Chitin: fulfilling a biomaterials promise. Elsevier Science, 20017
Chitin
Hierarchical architecture in nature
• Lobster exoskeleton: chitin and proteins assemble into hierarchical structures• Exoskeleton consists of chitin nanofibers
Lobsterexoskeleton
Acta Materialia 2005, 53: 4281 8
Bio-derived gas barrier materials
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P =
Q = vol / time
A = area h
Δp = pressure change
P = DS
QhAΔp
1 Barrer = [10−11 cm3 cm cm−2 s−1 mmHg−1]
Key figure ispermeability, P
Units: [cm3 µm m−2 d−1 kPa−1]
Bio-derived gas barrier materials
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High aspect-ratio composites used to increase diffusion path length
Barrier P difficult to achieve defects at interfaces dispersion of filler
Recyclability impacted
Chitin and Cellulose nanofibers offer an advantage if used in neat form.
Bio-derived gas barrier materials
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Nair , Zhu, Deng, RagauskasSustainable Chemical Processes 2014
Cellulose nanofibers show promise as barrier films
Sharma et al., RSC Advances 2014(Group of Prof. Yulin Deng)
PO2 = 0.01 cc um / m2 d kPa
PO2 = 0.17 cc um / m2 d kPaUntreated CNF
175 °C Treated CNF
Bio-derived gas barrier materials
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Only a few reports of barrier films involving chitin:
• Regenerated chitin films plasticized with glycerolPO2 = 0.003 barrer (35 °C)
• Composite of chitin nanowhiskers coated on PLA PO2 = 0.001 barrer
• No pure chitin films with high barrier properties (prior to our work)
International Journal of Biological Macromolecules 2012, 50, 69
Journal of Materials Chemistry A 2013, 1 1867
Challenges for both cellulose and chitin in applications
• InsolubilityOrganic Solvents
Atalla, R. H. and Isogai, A., in Polysaccharides : structural diversityand functional versatility, 2005 13
Challenges for both cellulose and chitin in applications• Insolubility
• Approaches to process cellulose / chitinRegeneration: dissolution followed by precipitation
• strong acids, bases or volatile organic solvents• disrupts intrinsically high crystallinity
Extraction and dispersion of nano-fibers Follow by assembly into film during drying
• Acid hydrolysis• Peroxide oxidation (TEMPO)• Grinding result in gelling suspensions• Ultrasonication cannot extract most crystalline α form• High-pressure homogenization Our approach
Chitin nanofibers (ChNFs): Wu and Meredith Biomacromolecules 2014, 15, 4614
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Chitin Nanofiber Generation
Crab shell
Chitin purification:deproteination and dimineralization
Purified chitin/water
Chitin nanofiber/water
dispersion
Mechanical shearing
Chitin nanofiber (20 nm)(pH 4)
Zeta potential curve of chitin nanofiber
Purified chitin (micro-size particles)
0.5 wt.% of chitin
Wu and Meredith Biomacromolecules 2014, 15, 4614 15
13C CP-MAS solid state NMR of purified chitin from crab shells
Degree of acetylation = 92.4%
Wu and Meredith Biomacromolecules 2014, 15, 4614 16
Morphology of Chitin
Beforehomogenizer
Afterhomogenizer(35 passes)
pH 4.1 pH 7.0
Wu and Meredith Biomacromolecules 2014, 15, 4614 17
Rheological Properties of DispersionsChNF/water
pH of 4.135 passes in homogenizer
ChNF/water pH of 4.1
4 passes in homogenizer
Wu and Meredith Biomacromolecules 2014, 15, 4614 18
Films from Chitin Nanofibers
Wu and Meredith Biomacromolecules 2014, 15, 461419
Mechanical Properties
ACS Appl. Mater. Interfaces 2013, 5, 4640−4647
Chitin nanofiber (ChNF) Film Cellulose (CNC) Film
Biomacromolecules 2014, 15, 4614
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Gas Kinetic
diameter (Å)
Permeability
(barrer)
H2 2.89 0.024
CO2 3.30 0.018
O2 3.46 0.006
N2 3.64 0.0034
CH4 3.80 0.0027
Gas permeabilities in ChNF films
0% relative humidityWu and Meredith Biomacromolecules 2014, 15, 4614 21
PO2 (barrer) PCO2 (barrer)PE 0.75-4.73 11.7-14.6PP 0.75-1.52, 4PET 0.015-0.076 0.3ChNF 0.006 0.018EVOH 1.5x10-5
CNF 1x10-7
0 % RH
Duan et al. Journal of Materials Chemistry A 2013, 1, 1867Gholizadeh et al. Mater. Des. 2007, 28, 2528Jarus et al. Polymer 2002, 43, 2401Tsai et al. Adv. Mater. 2005, 17, 1769
ChNF Compared to Other Films
Wu and Meredith Biomacromolecules 2014, 15, 4614 22
Chitin-based porous materials
Can we mimic and improve upon this intricate natural structure?
1 µm1 mm
(a) (b) (c)
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Freeze drying: freezing rate effect • Starting materials: chitin nanofiber (20nm)/water dispersion
• Processing approach:
Step 1. freeze this dispersion at different conditions: liquid nitrogen, -80 °C,
-20 °C, -20 °C (slow) (freezing rate: liquid nitrogen>-80 °C >-20 °C)
Step 2. sublimation of ice crystals by freeze drier
• Chitin nanofiber (20nm)/water dispersion: liquid nitrogen freezing(sample bottom touched the liquid nitrogen)
Pore size: 59.2±7.6 μm
Wu and Meredith, ACS Macro Letters, 2014, 3, 18524
Freeze drying: freezing rate effect
• Chitin nanofiber(20nm)/water dispersion: liquid nitrogen freezing
• Chitin nanofiber(20nm)/water dispersion: -80 OC freezing
Pore size: 96.2±12.0 μm
Pore size: 59.2±7.6 μm
Wu and Meredith, ACS Macro Letters, 2014, 3, 18525
Freeze drying: freezing rate effect
Enlarged top SEM image
• Chitin nanofiber(20nm)/water dispersion: -20 °C
Pore size: 3.2±0.4 μm
Wu and Meredith, ACS Macro Letters, 2014, 3, 18526
CompositesCNC-Filled Epoxy
with Meisha Shofner (MSE)
Xu, Girouard, Schueneman, Shofner, Meredith, Polymer, 2013 27
Conclusions
– CNFs and ChNFs extracted via chemical/mechanical processes
– Formed direct into neat CNF or ChNF films • Low permeability• High transparency • Good mechanical properties.
– Developed process for nanoporous chitin foams via freeze drying
– Useful for high-strength composites
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Acknowledgements• GT Renewable Bioproducts Institute• USDA (Greg Schueneman)• Jie Wu, former Ph.D. Student• Natalie Girouard, current Ph.D. Student• Michael Avidano, undergrad researcher• Meisha Shofner, MSE
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