Influence of filler size on the properties of poly(lactic acid) (PLA)/graphene nanoplatelet (GNP) nanocomposites

Poly(lactic acid) (PLA) composites reinforced with two types of graphite nanoplatelets varying in lateral size - small (GNP-S) and large (GNP-L)- were produced via melt compounding. Morphological, thermal, mechanical, and electrical properties were investigated to reveal the influence of particle size. Electron microscopy and X-ray diffraction showed well dispersed small GNP-S particles up to 10 wt.% loading, while large GNP-L particles started to agglomerate at loadings >= 7 wt.%. Addition of GNPs improved the Young's modulus of the composites by 10% and 24% for small and large nanoplatelets, respectively, the latter being among the highest reported for PLA/GNP systems. For GNP-L this larger increase could be partly explained by an increase in crystallinity while no such effect was observed for GNP-S. Conversely, GNP-L systems showed embrittlement while polymer yield was preserved for GNP-S. GNP-L resulted in a lower electrical percolation threshold. However, systems based on smaller GNP-S particles showed significantly enhanced conductivity and a reduction in percolation threshold after annealing. Heat distortion temperature (HDT) increased by up to 13 degrees C, with large GNP-L showing the slightly larger increase. Crown Copyright (C) 2016 Published by Elsevier Ltd. All rights reserved.