Influences of poly(lactic acid)-grafted carbon nanotube on thermal, mechanical, and electrical properties of poly(lactic acid)

Abstract

Poly(lactic acid)-grafted multiwalled carbon nanotubes (MWNT-g-PLA) were prepared by the direct melt-polycondensation of L-lactic acid with carboxylic acid-functionalized MWNT (MWNT-COOH) and then mixed with a commercially available neat PLA to prepare PLA/MWNT-g-PLA nanocomposites. Morphological, thermal, mechanical, and electrical characteristics of PLA/MWNT-g-PLA nanocomposites were investigated as a function of the MWNT content and compared with those of the neat PLA, PLA/MWNT, and PLA/MWNT-COOH nanocomposites. It was identified from FE-SEM images that PLA/MWNT-g-PLA nanocomposites exhibit good dispersion of MWNT-g-PLA in the PLA matrix, while PLA/MWNT and PLA/MWNT-COOH nanocomposites display MWNT aggregates. As a result, initial moduli and tensile strengths of PLA/MWNT-g-PLA composites are much higher than those of neat PLA, PLA/MWNT, and PLA/MWNT-COOH, which stems from the efficient reinforcing effect of MWNT-g-PLA in the PLA matrix. In addition, the crystallization rate of PLA/MWNT-g-PLA nanocomposites is faster than those of neat PLA, PLA/MWNT, and PLA/MWNT-COOH, since MWNT-g-PLA dispersed in the PLA matrix serves efficiently as a nucleating agent. It is interesting that, unlike PLA/MWNT nanocomposites, surface resistivities of PLA/MWNT-g-PLA nanocomposites did not change noticeably depending on the MWNT content, demonstrating that MWNTs in PLA/MWNT-g-PLA are wrapped with the PLA chains of MWNT-g-PLA. Copyright (C) 2008 John Wiley & Sons, Ltd.