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Cellulose- and Chitin-Based Coatings and Films
Carson Meredith
Professor
Chemical & Biomolecular Engineering
Georgia Tech
Atlanta, GA
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One Motivation - Packaging
• 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
www.foodproductiondaily.com
• 10% is flexible plastic
• 27% is rigid plastic
• Nearly all of these are petroleum-derived barrier
poly(ethylene terephthalate) (PET)
plastics
poly(vinylidene chloride))
Chem. Soc. Rev. 2011, 40, 5266-5281
Chem. Soc. Rev. 2014, 43, 588-610
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Motivation
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Other Motivations
• 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
Futuris
American
Process
GaTech
CAU
Swinburne
USDA-FPL
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Cellulose in wood and plant structures
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Estimated cellulose
nanocrystal
Like carbon fiber,
potential for highstrength
but 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, 2001
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Chitin
Hierarchical architecture in nature
Lobster
exoskeleton
•
Lobster exoskeleton: chitin and proteins assemble into hierarchical structures
•
Exoskeleton consists of chitin nanofibers
Acta Materialia 2005, 53: 4281
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Bio-derived gas barrier materials
Key figure is
permeability, P
Q = vol / time
A = area
h
Δp = pressure change
P = DS
Qh
P=
AΔp
Units: [cm3 µm m−2 d−1 kPa−1]
1 Barrer = [10−11 cm3 cm cm−2 s−1 mmHg−1]
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Bio-derived gas barrier materials
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.
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Bio-derived gas barrier materials
Cellulose nanofibers show promise as barrier films
PO2 = 0.17 cc um / m2 d kPa
Untreated CNF
PO2 = 0.01 cc um / m2 d kPa
175 °C Treated CNF
Nair , Zhu, Deng, Ragauskas
Sustainable Chemical Processes 2014
Sharma et al.,
RSC Advances 2014
(Group of Prof. Yulin Deng)
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Bio-derived gas barrier materials
Only a few reports of barrier films involving chitin:
• Regenerated chitin films plasticized with glycerol
PO2 = 0.003 barrer (35 °C) Journal of Materials Chemistry A
2013, 1 1867
• Composite of chitin nanowhiskers coated on PLA
PO2 = 0.001 barrer International Journal of Biological
Macromolecules 2012, 50, 69
• No pure chitin films with high barrier properties
(prior to our work)
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Challenges for both cellulose and chitin in
applications
• Insolubility
Organic Solvents
Atalla, R. H. and Isogai, A., in Polysaccharides : structural diversity
and functional versatility, 2005
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Challenges for both cellulose and chitin in
applications
Insolubility
•
• Approaches to process cellulose / chitin
Regeneration: 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
Chitin
Purified
Mechanical
chitin/water shearing nanofiber/water
dispersion
Chitin nanofiber (20 nm)
(pH 4)15, 4614
Wu and Meredith Biomacromolecules 2014,
Purified chitin (micro-size particles)
0.5 wt.% of chitin
Zeta potential curve of chitin
nanofiber
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13C
CP-MAS solid state NMR
of purified chitin from crab
shells
Degree of acetylation = 92.4%
Wu and Meredith Biomacromolecules 2014, 15, 4614
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Morphology of Chitin
pH 4.1
pH 7.0
Before
homogenizer
After
homogenizer
(35 passes)
Wu and Meredith Biomacromolecules 2014, 15, 4614
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Rheological Properties of Dispersions
ChNF/water
pH of 4.1
35 passes in homogenizer
ChNF/water
pH of 4.1
4 passes in homogenizer
Wu and Meredith Biomacromolecules 2014, 15, 4614
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Films from Chitin Nanofibers
Wu and Meredith Biomacromolecules 2014, 15, 4614
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Mechanical Properties
Chitin nanofiber (ChNF) Film
Biomacromolecules 2014, 15, 4614
Cellulose (CNC) Film
ACS Appl. Mater. Interfaces 2013, 5,
4640−4647
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Gas permeabilities in ChNF films
Kinetic
Permeability
diameter (Å)
(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
0% relative humidity
Wu and Meredith Biomacromolecules 2014, 15, 4614
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ChNF Compared to Other Films
PE
PP
PET
ChNF
EVOH
CNF
0 % RH
PO2 (barrer)
0.75-4.73
0.75-1.52,
0.015-0.076
0.006
1.5x10-5
1x10-7
PCO2 (barrer)
11.7-14.6
4
0.3
0.018
Duan et al. Journal of Materials Chemistry A 2013, 1, 1867
Gholizadeh et al. Mater. Des. 2007, 28, 2528
Jarus et al. Polymer 2002, 43, 2401
Tsai et al. Adv. Mater. 2005, 17, 1769
Wu and Meredith Biomacromolecules 2014, 15, 4614
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Chitin-based porous materials
(a)
(b)
(c)
1 mm
1 µm
Can we mimic and improve upon this intricate natural structure?
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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
Pore size: 59.2±7.6 μm
•
Chitin nanofiber (20nm)/water dispersion: liquid nitrogen freezing
(sample bottom touched the liquid nitrogen)
Wu and Meredith, ACS Macro Letters, 2014, 3, 185
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Freeze drying: freezing rate effect
Pore size: 59.2±7.6 μm
•
Chitin nanofiber(20nm)/water dispersion: liquid nitrogen freezing
Pore size: 96.2±12.0 μm
•
Chitin nanofiber(20nm)/water dispersion: -80 OC freezing
Wu and Meredith, ACS Macro Letters, 2014, 3, 185
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Freeze drying: freezing rate effect
Pore size: 3.2±0.4 μm
•
Chitin nanofiber(20nm)/water dispersion: -20 °C
Enlarged top SEM image
Wu and Meredith, ACS Macro Letters, 2014, 3, 185
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Composites
CNC-Filled Epoxy
with Meisha Shofner (MSE)
Xu, Girouard, Schueneman,
Shofner, Meredith, Polymer, 2013
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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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