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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. Nanotube composite materials are getting stronger, but…. …not there yet…. Nanotube Composite Materials.

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carbon nanotube polymer composites a review of recent developments

Carbon Nanotube Polymer Composites: A Review of Recent Developments

Rodney Andrews & Matthew Weisenberger

University of Kentucky

Center for Applied Energy Research

nanotube composite materials
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
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:
    • 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
mwnt matrix interface
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.

interphase region
Interphase Region
  • Nanotube effecting crystallization of PP
  • Sandler et al, J MacroMol Science B, B42(3&4), pp 479-488,2003
two approaches for surface modification of mwnts
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
Polymer Wrapping
  • Polycarbonate wrapping of MWNT (Ruoff group)

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

shi et al polymer wrapping
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.

Co-valent Functionalization

Epoxide terminated molecule and

carboxylated nanotubes

Schadler, RPIAndrews, UK

velasco santos et al
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 Compositesthrough Chemical Functionalization. Chemistry of Materials, 2003. 15: p. 4470-4475.
in situ polymerization of pan
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
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.
baughman group
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
kearns et al pp swnt fibers
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
kumar et al
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
kumar pbo swnt fibers
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.
electrospun fibers
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
  • 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

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”