Transcript Document 7167815

Carbon Nanotube Polymer
Composites: A Review of Recent
Developments
Rodney Andrews & Matthew Weisenberger
University of Kentucky
Center for Applied Energy Research
Nanotube composite
materials are getting
stronger, but…
…not there yet…
Nanotube Composite Materials
• Engineering MWNT composite materials
• Lighter, stronger, tougher materials
• Lighter automobiles with improved safety
• Composite armor for aircraft, ships and tanks
• Conductive polymers and coatings
• Antistatic or EMI shielding coatings
• Improved process economics for coatings, paints
• Thermally conductive polymers
• Waste heat management or heat piping
• Multifunctional materials
High Strength Fibers
 To achieve a high strength nanotube fiber:
 High strength nanotubes (> 100 GPa)
 Good stress transfer from matrix to nanotube
 Or, nanotube to nanotube bonding
 High loadings of nanotubes
 Alignment of nanotubes (< 5° off-axis)
 Perfect fibers
 Each defect is a separate failure site
Issues at the Interface
 Interfacial region, or interaction zone,
can have different properties than the
bulk polymer:
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chain mobility,
entanglement density,
crosslink density
geometrical conformation
 Unique reinforcement mechanism
 diameter is of the same size scale as the
radius of gyration
 can lead to different modes of interactions
with the polymer.
 possible wrapping of polymer chains
around carbon
Bulk
interphase
nanotube
MWNT/Matrix Interface
 The volume of matrix that
can be affected by the
nanotube surface is
significantly higher than
that for traditional
composites due to the
high specific surface
area.
 30nm diameter
nanotubes have about
150 times more surface
area than 5 µm fibers for
the same filler volume
fraction
S nano-filler
1000
S 5µm fiber
800
600
400
200
0
0
20
40
60
80
Df (nm)
Ding, W., et al., Direct observation of polymer sheathing in carbon nanotube-polycarbonate
composites. Nano Letters, 2003. 3(11): p. 1593-1597.
100
Interphase Region
 Nanotube effecting crystallization of PP
 Sandler et al, J MacroMol Science B, B42(3&4), pp 479488,2003
Two Approaches for Surface
Modification of MWNTS
 Non-covalent attachment of molecules
 van der Waals forces: polymer chain wrapping
 Alters the MWNT surface to be compatible with the bulk polymer
 Advantage: perfect structure of MWNT is unaltered
 mechanical properties will not be reduced.
 Disadvantage: forces between wrapping molecule / MWNT
maybe weak
 the efficiency of the load transfer might be low.
 Covalent bonding of functional groups to walls and caps
 Advantage: May improve the efficiency of load transfer
 Specific to a given system – crosslinking possibilities
 Disadvantage: might introduce defects on the walls of the MWNT
 These defects will lower the strength of the reinforcing
component.
Polymer Wrapping
 Polycarbonate wrapping of MWNT (Ruoff group)
Ding, W., et al., Direct observation of polymer sheathing in carbon nanotubepolycarbonate composites. Nano Letters, 2003. 3(11): p. 1593-1597.
Shi et al - Polymer Wrapping
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Activation/etching of MWNT surface
Plasma deposition of 2-7 nm polystyrene
Improved dispersion
Increased tensile strength and modulus
Clearly defined interfacial adhesion layer
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Shi, D., et al., Plasma coating of carbon nanofibers for enhanced dispersion and interfacial bonding in polymer composites.
Applied Physics Letters, 2003. 83(25): p. 5301-5303.
Co-valent Functionalization
Epoxide terminated molecule and
carboxylated nanotubes
Schadler, RPI
Andrews, UK
Velasco-Santos et. Al.
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Functionalization and in situ polymerization of PMMA
COOH and COO- functionalities
in situ polymerization with methyl methacrylate
increase in mechanical properties for both nanotube
composites compared to neat polymer
 improvements in strength and modulus of the
functionalized nanotube composite compared to
unfunctionalized nanotubes
 The authors conclude that “functionalization, in
combination with in situ polymerization , is an excellent
method for producing truly synergetic composite materials
with carbon nanotubes”
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Velasco-Santos, C., et al., Improvement of Thermal and Mechanical Properties of Carbon Nanotube
Composites through Chemical Functionalization. Chemistry of Materials, 2003. 15: p. 4470-4475.
In Situ Polymerization of PAN
 Acrylate-functionalized
MWNT which have been
carboxilated
 Free-radical
polymerization of
acrylonitrile in which
MWNTs are dispersed
 Hope to covalentely
incorporate MWNTs
functionalized with acrylic
groups
Strong Matrix Fiber Interaction
 SEM images of fracture surfaces indicate excellent
interaction with PAN matrix, note ‘balling up’ of
polymer bound to the MWNT surface. This is a result
of elastic recoil of this polymer sheath as the fiber is
fractured and these mispMWNTs are pulled out.
20 wt% MWNT/Carbon Fiber
Baughman Group
 poly(vinyl alcohol) fibers
 containing 60 wt.% SWNTs
 tensile strength of 1.8GPa
 80GPa modulus for pre-strained fibers
 High toughness
 energies-to-break of 570 J/g
 greater than dragline spider silk and Kevlar
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Dalton, A.B., et al., Super-tough carbon-nanotube fibres. NATURE, 2003. 423: p. 703
Kearns et al – PP/SWNT Fibers
 SWNT were dispersed into polypropylene
 via solution processing with dispersion via ultrasonic energy
 melt spinning into filaments
 40% increase in tensile strength at 1wt.% SWNT
addition, to 1.03 GPa.
 At higher loadings (1.5 and 2 wt%), fiber spinning
became more difficult
 reductions in tensile properties
 “NTs may act as crystallite seeds”
 changes in fiber morphology, spinning behavior
 attributable to polymer crystal structure.
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Kearns, J.C. and R.L. Shambaugh, Polypropylene Fibers Reinforced with Carbon Nanotubes.
Journal of Applied Polymer Science, 2002. 86: p. 2079-2084
Kumar et al
 SWNT/Polymer Fibers
 PMMA
 PP
 PAN
 Fabricated fibers with 1 to 10 wt% NT
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Increases in modulus (100%+)
Increases in toughness
Increase in compressive strength
Decrease in elongation to break
Decreasing tensile strength
Kumar – PBO/SWNT Fibers
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high purity SWNT (99% purity)
PBO poly(phenylene benzobisoxazole)
10 wt% SWNT
20% increase in tensile modulus
60 % increase in tensile strength (~3.5 GPa)
 PBO is already a high strength fiber
 40% increase in elongation to break
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Kumar, S., et al., Fibers from polypropylene/nano carbon fiber composites. Polymer, 2002. 43: p. 17011703.
Kumar, S., et al., Synthesis, Structure, and Properties of PBO/SWNT Composites. Macromolecules, 2002.
35: p. 9039-9043.
Sreekumar, T.V., et al., Polyacrylonitrile Single-Walled Carbon Nanotube Composite Fibers. Advanced
Materials, 2004. 16(1): p. 58-61.
Electrospun Fibers
 (latest Science article)
 Leaders in Field
 Frank Ko – Drexel University
 ESpin Technologies (TN)
 Ko has done extensive work for DoD
 Reasonable strengths, but poor transfer
fibril to fibril
 Not a contiguous graphite structure
Conclusions
 Nanotubes are > 150 GPa in strength.
 Strain-to-break of 10 to 20%
 Should allow 100 GPa composites
 Challenges still exist
 Stress transfer / straining the tubes
 Controlling the interface
 Eliminating defects at high alignment
 Work is progressing among many groups
Acknowledgements
University of Kentucky
Center for Applied Energy Research
 Financial Support of the Kentucky Science and Engineering
Foundation under grant KSEF-296-RDE-003 for “Ultrahigh
Strength Carbon Nanotube Composite Fibers”
Questions???