Effect of Nanotube Functionalization on the Properties of Single-Walled Carbon Nanotube/Polyurethane Composites

FABIÁN BUFFA; GUSTAVO A. ABRAHAM; BRIAN P. GRADY; DANIEL E. RESASCO

JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS

John Wiley & Sons, Inc.

Año: 2007 vol. 45 p. 490 - 501

0887-6266

A commercially available aliphatic thermoplastic polyurethane formulatedwith a methylene bis(cyclohexyl) diisocyanate hard segment and a poly(tetramethyleneoxide) soft segment and chain-extended with 1,4-butanediol was dissolved in dimethylformamideand mixed with dispersed single-walled carbon nanotubes. The propertiesof composites made with unfunctionalized nanotubes were compared with the propertiesof composites made with nanotubes functionalized to contain hydroxyl groups.Functionalization almost eliminated the conductivity of the tubes according to the conductivityof the composites above the percolation threshold. In most cases, functionalizedand unfunctionalized tubes yielded composites with statistically identical mechanicalproperties. However, composites made with functionalized tubes did have a slightlyhigher modulus in the rubbery plateau region at higher nanotube fractions. SmallangleX-ray scattering patterns indicated that the dispersion reached a plateau in theunfunctionalized composites that was consistent with the plateau in the rubbery plateauregion. The room-temperature modulus and tensile strength increase was proportionallyhigher than almost all increases seen previously in thermoplastic polyurethanes;however, the increase was still an order of magnitude below what has beenreported for the best nanotube–polymer systems. Nanotube addition increased thehard-segment glass transition temperature slightly, whereas the soft-segment glasstransition was so diffuse that no conclusions could be drawn. Unfunctionalized tubessuppressed the crystallization of the hard segment; whereas functionalized tubes hadno effect.