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

                                     

…not there yet…

Nanotube composite materials are getting stronger, but…

Nanotube Composite MaterialsNanotube Composite MaterialsNanotube Composite MaterialsNanotube Composite Materials• Engineering MWNT composite materialsEngineering MWNT composite materials

• Lighter, stronger, tougher materialsLighter, stronger, tougher materials• Lighter automobiles with improved safetyLighter automobiles with improved safety• Composite armor for aircraft, ships and tanksComposite armor for aircraft, ships and tanks

• Conductive polymers and coatingsConductive polymers and coatings• Antistatic or EMI shielding coatingsAntistatic or EMI shielding coatings• Improved process economics for coatings, paintsImproved process economics for coatings, paints

• Thermally conductive polymersThermally conductive polymers• Waste heat management or heat pipingWaste heat management or heat piping

• Multifunctional materialsMultifunctional materials

High Strength FibersHigh 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

Bulk

interphase

nanotube

MWNT/Matrix InterfaceMWNT/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

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S nano-filler S 5µm fiber

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Df (nm)

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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 WrappingPolymer 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.

Shi et al - Polymer WrappingShi 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

Schadler, RPIAndrews, UK

Epoxide terminated molecule and carboxylated nanotubes

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 Composites through Chemical Functionalization. Chemistry of Materials, 2003. 15: p. 4470-4475.

In Situ Polymerization of PANIn Situ Polymerization of PAN Acrylate-functionalized Acrylate-functionalized

MWNT which have been MWNT which have been carboxilated carboxilated

Free-radical Free-radical polymerization of polymerization of acrylonitrile in which acrylonitrile in which MWNTs are dispersedMWNTs are dispersed

Hope to covalentely Hope to covalentely incorporate MWNTs incorporate MWNTs functionalized with acrylic functionalized with acrylic groupsgroups

Strong Matrix Fiber InteractionStrong 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 Fiber20 wt% MWNT/Carbon Fiber

Baughman GroupBaughman 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 FibersKearns 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 alKumar 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 FibersKumar – 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 FibersElectrospun 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

ConclusionsConclusions 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

AcknowledgementsAcknowledgements

University of KentuckyCenter for Applied Energy

Research

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

Questions???Questions???