Multiple synergies for enhancing the toughening efficiency: toward fully biodegradable polylactide-based engineering plastics with superior toughness, strength and heat resistance

Melt blending with biodegradable poly(butylene adipate-co-terephthalate) (PBAT) is a widely used approach for toughening poly(l-lactide) (PLLA). However, a high PBAT addition (30 wt%) is typically required to achieve supertoughness of PLLA, despite extensive efforts to improve toughening efficiency. Herein, the PLLA/PBAT blends were subjected to a simple one-pot melt blending with an epoxy-functional compatibilizer (ADR) and poly(d-lactide) (PDLA). The enhanced interfacial adhesion resulting from ADR-induced reactive compatibilization, combined with the elevated melt viscosity of the PLLA matrix caused by the generation of stereocomplex (sc) crystallites through PLLA-PDLA interactions, results in a morphological transition from a sea-island to a co-continuous structure. Concurrently, sc crystallites accelerate the PLLA matrix crystallization, achieving a highly crystalline matrix after brief melt crystallization. Owing to the synergistic effects of strong interfacial adhesion, co-continuous structure and highly crystalline matrix, the toughening efficiency of PBAT is markedly enhanced. Consequently, the notched impact strength of PLLA reaches 58.9 kJ/m² with only 15 wt% PBAT. Additionally, the reduced PBAT content coupled with increased matrix crystallinity endows the blend with high tensile yield strength (57.5 MPa) and heat resistance (Vicat softening temperature up to 156.4 °C). The comprehensive performance of the resulting blend surpasses that of certain commercially available non-biodegradable engineering plastics, potentially expanding the application of fully biodegradable polylactide-based alloys in engineering fields.