Analysis of the hydrolysis behavior of poly(lactic acid) (PLA) and prediction of molecular weight distribution changes via the kinetic Monte Carlo method

Poly(lactic acid) (PLA) is a biobased and biodegradable plastic derived from natural resources. In this study, the degradation mechanism of PLA during hydrolysis was experimentally verified, and a computational strategy was constructed to predict its degradation behavior. The reaction rates and solid-state structure of PLA during hydrolysis were measured, and the hydrolysis behavior of the crystalline and amorphous phases was investigated. The results indicated that the molecular chains were randomly cleaved in the amorphous phase but were cleaved only on the folding surface of the lamellar crystals in the crystalline phase. Furthermore, the degradation behavior of amorphous and semicrystalline PLA during hydrolysis was modeled and simulated using the kinetic Monte Carlo method. The specific degradation behavior of the crystalline phase was described by considering the distribution of lamellar crystals and the dependence of the degradation rate on the molecular chain position. With this model, the molecular weight distribution and weight loss of PLA can be predicted. This study is the first to construct a degradation model based on a solid-state structure that can predict not only the average molecular weight but also the molecular weight distribution.