Constructing segregated structure with multiscale stereocomplex crystallites toward synchronously enhancing the thermal conductivity and thermo-mechanical properties of the poly(l-lactic acid) composites

Abstract

Based on the rapid development of electronic device performance, heat dissipation has become an urgent problem in packaging materials relating to polymeric composites. Meantime, the severe environmental pollution and energy crisis have also become great problems. Therefore, the development of renewable polymers with high thermal conductivity is a considerable way to reduce the dependence on petroleum-based polymers. Here, we report a convenient method for the preparation of renewable high thermal conductivity composites. Firstly, the stereocomplex crystallites (SCs) granules are prepared through the melt blending of poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA) at a mass ratio of 1:1. Then, the PLLA/graphene nanoplatelets (PLLA/GNP) composite is coated on the surface of the SC granules by solution blending. Finally, the segregated and double-percolated structures with multiscale SCs form in the PLLA/GNP@SC composites through the compression molding method. The results show that the thermal conductivity of the PLLA/GNP@SC composites are much better than that of the PLLA/GNP composite under the same load of GNPs. The thermal conductivity of the PLLA/GNP@SC composite containing only 2 wt % GNPs reaches 0.96 W m−1K−1, which is 336.4% and 71.4% higher than those of the pure PLLA (0.22 W m−1K−1) and the PLLA/GNP (0.56 W m−1K−1) composite, respectively. The PLLA/GNP@SC composites also exhibit good mechanical properties at high temperatures due to the formed SC microcrystals at the interface between segregated SC granules and continuous PLLA/GNP phase. Moreover, the PLLA/GNP@SC composites also exhibit ultrahigh thermal resistance, flame retardance, and electrical conductivity. This work provides a new way for manufacturing the green multifunctional high thermal conductivity composite.