Heat resistant and thermally conductive polylactide composites achieved by stereocomplex crystallite tailored carbon nanofiber network

Abstract

As a renewable and environmentally friendly polymer, poly(L-lactic acid) (PLLA) has immense feasibility to replace traditional thermoplastics. However, the present application of PLLA as an engineering plastic in microelectronic devices still faces some obstacles, such as poor heat resistance and low thermal conductivity. In the present work, a facile solution compounding processing was employed to comprise poly(D-lactic acid) (PDLA) and carbon nanofibers (CNFs) into PLLA composites. Microstructure characterizations showed that the presence of PDLA not only induced a large amount of stereocomplex crystallites (SCs) but also promoted denser CNF network in the composites. Consequently, in contrast to the PLLA/CNF samples, the PLLA/PDLA/CNF samples showed largely promoted heat resistance and thermal conductivity. At 50 wt% PDLA and 20 wt% CNFs, the sample showed the heat resistant temperature (HRT) of 196.7 °C, about 56.7 °C greater than that of the PLLA/CNF (20 wt%), and the thermal conductivity of 2.34 Wm-1K−1, 1014% greater than that of the PLLA. The mechanisms were largely ascribed to the SCs formation, which promoted the stacking of CNFs to a certain extent. Specifically, SCs organized into a compact physical network at relatively high PDLA content, which exhibited a ‘locking’ effect on dispersion of CNFs, leading to the efficient lap of thermally conductive filler in the composites. This work indicates that in-situ forming SCs is a promising strategy for regulating the filler’s thermal conductive network in PLLA-based polymer, and the composites may be alternative engineering plastics of the future.