Simultaneous Enhancement of Mechanical, Rheological, Heat Resistance, and Thermal/Electrical Properties of Poly(L-lactide)/Poly(D-lactide)/Carbon Fibers Composites

In this work, poly(L-lactide) (PLLA)/poly(D-lactide) (PDLA)/carbon fiber (CF) composites with different PDLA content were prepared by simple melt blending. The stereocomplex (SC) crystallites were in situ formed. The effects of CFs and SC crystallites on the morphology, crystallization, rheological behaviors, mechanical properties, heat resistance, thermal and electrical conductivity of composites were investigated. The SC crystallites acted as nucleating agents of PLLA to accelerate the crystallization of PLLA, improve the degree of crystallinity, and refine spherical crystals, which led to a more homogeneous and dense dispersion of CFs. For the PLLA/PDLA/CF composite with 10 wt% PDLA, attributing to the synergistic effect of CFs and SC crystallites, vicat softening temperature (VST) was increased by about 100 ℃ over neat PLLA. The thermal conductivity increased from 0.21 W (mK)⁻¹ of neat PLLA to 0.47 W (mK)⁻¹, and surface resistivity decreased dramatically by about 8 orders of magnitude. More importantly, an increases of 156% and 29.2% were achieved in the tensile modulus and strength of composite with 10 wt % PDLA compared to neat PLLA. Melt viscosity and elasticity were also significantly improved with the addition of CFs and PDLA. The unusual combination of the improved mechanical and rheological performances, thermal resistance, thermal and electrical conductivity established in the degradable composites meets the properties required for a wider range of PLLA applications.