Improvement in melt flow property and flexibility of poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide) by chain extension reaction for potential use as flexible bioplastics

Poly(L-lactide) (PLLA) is a biodegradable bioplastic that has been widely investigated for use instead of petroleum-based plastics. However, its practical applications have been limited by its brittleness. Herein, a high molecular weight triblock copolymer of poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide) (PLLA-PEG-PLLA) was synthesized by ring-opening polymerization of L-lactide using stannous octoate and PEG as the initiating system. The effect of an epoxy-based chain extender on the thermal properties, melt flow index (MFI), phase morphology and tensile properties of the PLLA-PEG-PLLA were investigated and compared to PLLA homopolymer. Chain-extended PLLA-PEG-PLLA and its films were prepared by reactive melt blending and compression molding, respectively. The flexible PEG blocks significantly improved both crystallization of PLLA blocks and strain at break of PLLA-PEG-PLLA films. The chain extension can decrease MFI of both the PLLA and PLLA-PEG-PLLA but their crystallizabilities were suppressed. All the PLLA-PEG-PLLA films with and without chain extension had no phase separation. The tensile properties of PLLA-PEG-PLLA films increased by the chain extension. The results showed that the chain-extended PLLA-PEG-PLLA have potential for use as highly flexible bioplastics. (c) 2018 Elsevier Ltd. All rights reserved.