Study on the atomic scale of thermal and thermo-oxidative degradation of polylactic acid via reactive molecular dynamics simulation

Abstract

The reactive force field molecular dynamics (ReaxFF-MD) simulations were performed on polylactic acid (PLA) for the first time to understand its thermal and thermo-oxidative degradation mechanisms. The main degradation products of PLA observed in actual experiments were well reproduced by ReaxFF-MD simulations. The results showed that the initial thermal degradation pathway for the PLA was the homolytic cleavage of CO bond next to the ester group, followed by CO bond breaking in the ester group and CC bond cleavage. Carbon monoxide, carbon dioxide and acetaldehyde were the major volatile products generated following the thermal degradation after being initiated by the homolytic scission. In thermo-oxidative degradation simulation, the alkyl peroxide and hydroperoxide were formed, which degraded into alkoxyl and hydroxyl radicals, resulting in the increase of the lower carbon fraction (C1–4). This study would provide meaningful theoretical guidance for the mechanisms of thermal and thermo-oxidative degradation of PLA.