1. Carbon Nanotube Polymer Composites: A Review of Recent Developments
Rodney Andrews & Matthew Weisenberger
University of Kentucky
Center for Applied Energy Research

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

3. 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

4. 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

5. 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

6. 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, (11): p

7. Interphase Region Nanotube effecting crystallization of PP
Sandler et al, J MacroMol Science B, B42(3&4), pp ,2003

8. 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.

9. Polymer Wrapping Polycarbonate wrapping of MWNT (Ruoff group)
Ding, W., et al., Direct observation of polymer sheathing in carbon nanotube-polycarbonate composites. Nano Letters, (11): p

10. 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, (25): p

11. Co-valent Functionalization
Epoxide terminated molecule and
carboxylated nanotubes
Schadler, RPI Andrews, UK

12. 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, : p

13. 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

14. 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.

15. 20 wt% MWNT/Carbon Fiber

16. Baughman Group poly(vinyl alcohol) fibers tensile strength of 1.8GPa
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, : p. 703

17. 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, : p

18. Kumar et al SWNT/Polymer Fibers Fabricated fibers with 1 to 10 wt% NT
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

19. 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, : p
Kumar, S., et al., Synthesis, Structure, and Properties of PBO/SWNT Composites. Macromolecules, : p
Sreekumar, T.V., et al., Polyacrylonitrile Single-Walled Carbon Nanotube Composite Fibers. Advanced Materials, (1): p

20. 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

21. 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

22. Center for Applied Energy Research
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”

23. Questions???