Stereocomplexed Poly(lactide) Composites toward Engineering Plastics with Superior Toughness, Heat Resistance and Anti-hydrolysis

Abstract

Poly(lactide), PLA, suffers from brittleness and low heat deflection temperature (HDT), which limits its application as an engineering plastic. In this work, poly(L-lactide)/poly(D-lactide)/ethylene-vinyl acetate-glycidyl methacrylate random copolymer (PLLA/PDLA/EVM-GMA = 1/1/x) composites were prepared by melt blending, and the in situ formed EVM-g-PLA copolymers improved the compatibility between PLA and EVM-GMA. Subsequently, the blends were subjected to a two-step annealing process during compression molding, i.e. first annealing at 120 °C to rapidly form a certain amount of stereocomplex (sc) crystallites as nucleation sites, and then annealing at 200 °C to guide the formation of new sc crystallites. Both differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD) measurements confirmed the formation of highly stereocomplexed PLA products. Mechanical results showed that the PLLA/PDLA blend with 20 wt% of EVM-GMA had a notched impact strength up to 65 kJ/m2 and an elongation at break of 48%, while maintaining a tensile strength of 40 MPa. Meanwhile, dynamic mechanical analysis (DMA) and heat deflection tests showed that the PLA composite had an HDT up to 142 °C which is 90 °C higher than that of normal PLA products. Scanning electron microscopy (SEM) confirmed the fine dispersion of EVM-GMA particles, which facilitated to understand the toughening mechanism. Furthermore, the highly stereocomplexed PLA composites simultaneously exhibited excellent chemical and hydrolysis resistance. Therefore, these fascinating properties may extend the application range of sc-PLA material as an engineering bioplastic.