Supertoughened Polylactide Binary Blend with High Heat Deflection Temperature Achieved by Thermal Annealing above the Glass Transition Temperature

Through thermal annealing above the glass transition temperature, a supertoughened binary blend with the highest notched Izod impact strength of 98 KJ/m² was achieved, which was about 52 times of that of neat polylactide (PLA; 1.9 KJ/m²). The binary blend was composed of biocompatible and biodegradable PLA and ethylene–acrylic ester–glycidyl methacrylate terpolymer (EGMA) elastomer at the composition of 80/20 PLA/EGMA. For one toughened binary blend with the notched Izod impact strength of 94 KJ/m², its tensile elongation at break was kept above 120%. Moreover, this supertoughened binary blend also displayed a much higher heat deflection temperature for application. Thermal annealing induced crystallization of the PLA matrix in the blend, and a linear correlation between the notched Izod impact strength and crystallinity was revealed. The possible toughening mechanism for the PLA/EGMA 80/20 blend with thermal annealing was analyzed from the viewpoint of negative pressure effects, as imposed on EGMA elastomeric particles during the quench process and thermal annealing thereafter. Decreases of the glass transition temperatures for the EGMA elastomeric particles in the blend were observed for both the quench and thermal annealing processes, which originated from asymmetric thermal shrinkages between the EGMA elastomeric phase and PLA matrix phase.