Carbon Nanotube Polymer Composites: A Review of Recent Developments

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Carbon Nanotube Polymer Composites A Review of
Recent Developments

• Rodney Andrews Matthew Weisenberger
• University of Kentucky
• Center for Applied Energy Research

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Nanotube composite materials are getting
stronger, but
not there yet
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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

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High Strength Fibers

• To achieve a high strength nanotube fiber
• High strength nanotubes (gt 100 GPa)
• Good stress transfer from matrix to nanotube
• Or, nanotube to nanotube bonding
• High loadings of nanotubes
• Alignment of nanotubes (lt 5 off-axis)
• Perfect fibers
• Each defect is a separate failure site

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Issues at the Interface

• Interfacial region, or interaction zone, can have
  different properties than the bulk polymer
• 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

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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

Ding, W., et al., Direct observation of polymer
sheathing in carbon nanotube-polycarbonate
composites. Nano Letters, 2003. 3(11) p.
1593-1597.
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Interphase Region

• Nanotube effecting crystallization of PP
• Sandler et al, J MacroMol Science B, B42(34), pp
  479-488,2003

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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.

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Polymer Wrapping

• Polycarbonate wrapping of MWNT (Ruoff group)

Ding, W., et al., Direct observation of polymer
sheathing in carbon nanotube-polycarbonate
composites. Nano Letters, 2003. 3(11) p.
1593-1597.
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Shi et al - Polymer Wrapping

• Activation/etching of MWNT surface
• Plasma deposition of 2-7 nm polystyrene
• Improved dispersion
• Increased tensile strength and modulus
• Clearly defined interfacial adhesion layer
• 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.

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Co-valent Functionalization
Epoxide terminated molecule and carboxylated
nanotubes
Schadler, RPIAndrews, UK
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Velasco-Santos et. Al.

• 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
• 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.

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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

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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.

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20 wt MWNT/Carbon Fiber
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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
• Dalton, A.B., et al., Super-tough carbon-nanotube
  fibres. NATURE, 2003. 423 p. 703

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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.
• Kearns, J.C. and R.L. Shambaugh, Polypropylene
  Fibers Reinforced with Carbon Nanotubes. Journal
  of Applied Polymer Science, 2002. 86 p.
  2079-2084

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Kumar et al

• SWNT/Polymer Fibers
• PMMA
• PP
• PAN
• Fabricated fibers with 1 to 10 wt NT
• Increases in modulus (100)
• Increases in toughness
• Increase in compressive strength
• Decrease in elongation to break
• Decreasing tensile strength

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Kumar PBO/SWNT Fibers

• 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
• Kumar, S., et al., Fibers from polypropylene/nano
  carbon fiber composites. Polymer, 2002. 43 p.
  1701-1703.
• 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.

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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

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Conclusions

• Nanotubes are gt 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

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Acknowledgements

• Financial Support of the Kentucky Science and
  Engineering Foundation under grant
  KSEF-296-RDE-003 for Ultrahigh Strength Carbon
  Nanotube Composite Fibers

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Questions???