Toughened transparent poly(L-lactic acid)/poly(D-lactide)-b-poly (butadiene)-b-poly(D-lactide) blended film with balanced strength

Tough and transparent poly(L-lactic acid)/poly(D-lactide)-b-poly(butadiene)-b-poly(D-lactide) (PLLA/PDLA-PB-PDLA) film with balanced strength was obtained. The PDLA-PB-PDLA triblock copolymer was firstly synthesized by ring-opening polymerization (ROP) of D-lactide using bihydroyl-terminated polybutadiene as macroinitiator, and then the obtained triblock copolymer was mixed with PLLA in solution. The blended films kept in good transparence even when the loading of PDLA-PB-PDLA reached to 15 wt%. Meanwhile, the elongation at break of the PLLA/PDLA-PB-PDLA film increased by similar to 10 times without a significant reduction in tensile strength as compared with that of pure PLLA. The mechanical property was ascribed to the synergetic effect of the flexible PB chains and the stereocomplex crystals formed between PLLA matrix and PDLA chains. Salami-like dispersed-phase with nanometer scales was observed, which would contribute to the transparency of the blended film. The tensile fractured morphologies indicated that shear yield of the matrix and cavitation might be the major toughening mechanism of PLLA/PDLA-PB-PDLA film.

Automated summary

A tough and transparent film of poly(L-lactic acid)/poly(D-lactide)-b-poly(butadiene)-b-poly(D-lactide) (PLLA/PDLA-PB-PDLA) with balanced strength was obtained. The film was achieved by synthesizing PDLA-PB-PDLA triblock copolymer using ring-opening polymerization and then blending it with PLLA. The blended films exhibited good transparency even with a high loading of PDLA-PB-PDLA. The enhanced mechanical properties were attributed to the synergistic effect of flexible PB chains and stereocomplex crystals formed between PLLA matrix and PDLA chains.