Polylactide/exfoliated graphite nanocomposites with enhanced thermal stability, mechanical modulus, and electrical conductivity

We have prepared a series of polylactide/exfoliated graphite (PLA/EG) nanocomposites by melt-compounding and investigated their morphology, structures, thermal stability, mechanical, and electrical properties. For PLA/EG nanocomposites, EG was prepared by the acid treatment and following rapid thermal expansion of micron-sized crystalline natural graphite (NG), and it was characterized to be composed of disordered graphite nanoplatelets. It was revealed that graphite nanoplatelets of PLA/EG nanocomposites were dispersed homogeneously in the PLA matrix without forming the crystalline aggregates, unlike PLA/NG composites. Thermal degradation temperatures of PLA/EG nanocomposites increased substantially with the increment of EG content up to ~3 wt %, whereas those of PLA/NG composites remained constant regardless of the NG content. For instance, thermal degradation temperature of PLA/EG nanocomposite with only 0.5 wt % EG was improved by ~10 K over PLA homopolymer. Young's moduli of PLA/EG nanocomposites increased noticeably with the increment of EG content up to ~3 wt %, compared with PLA/NG composites. The percolation threshold for electrical conduction of PLA/EG nanocomposites was found to be at 3-5 wt % EG, which is far lower graphite content than that (10-15 wt % NG) of PLA/NG composites.