High Melt Performance Poly (lactic acid) with Dual Hybrid Long Branching Chains Prepared by Chain Degradation and Restructuring

Abstract

Long chain branched structure (LCBs) is the critical to upgrade the poly (lactic acid) (PLA) melt performance, while introducing LCBs via chain restructuring by melt transesterification features higher-efficiency, environment-friendly and gel-free properties. However, severe degradation associated with excessive transesterification renders the branching reaction non-dominant, resulting in a significantly narrow processing window for LCBs formation. Herein, a new strategy, dual hybrid branching (DHB), was put forward to overcome the challenges. Specifically, surface-aminated nano-ZnO (SAN-ZnO) was applied as a transesterification accelerant to prepare LCB-PLA via melt transesterification between high molecular weight PLA and low molar mass monomer trimethylolpropane triacrylate (TMPTA) in an internal mixer. Moreover, amidogens on the surface of SAN-ZnO was capable to collect the degraded PLA chains (PLA-COOH) and in situ react with their carboxyl thermal groups via amidation. Benefiting from DHB to facilitate LCBs formation and restrain excessive degradation, the melt performance of PLA, especially the melt strength, was obviously improved to over 37 cN compared with pristine PLA (4 cN), and the cold crystallization occurred earlier owing to the DHB chain structure.