In‐situ experimental study on the hydrolysis and pyrolysis processes of polylactic acid

Abstract

In order to better understand the hydrolysis and pyrolysis process of polylactic acid (PLA), we carried out in‐situ experiments by observing the decomposition process of PLA at high temperature (up to 285°C) in both aqueous and anhydrous environments through fused silica capillary reactor (FSCR) combined with Raman spectroscopy analysis. By analyzing the strength change of characteristic peaks of PLA with increasing temperature, it was found that the initial melting temperature of PLA, in both the hydrolysis and pyrolysis processes, is around 170°C. Based on infrared spectroscopy analysis, it was found that the products of PLA pyrolysis are CO2, CH3CHCO, and CH3CHO, indicating that the pyrolysis process of PLA results from a free radical reaction. By comparing the Raman peak area ratios at different peak positions at different temperatures, it was found that the hydrolysis process of PLA mainly involves breaking the COC and CCO bonds of PLA, producing lactic acid, ethanol, CO2, and H2O. The hydrolysis reaction rate of PLA increases with the increase of temperature and exhibits a slow‐fast‐slow S‐shaped trend. The kinetic process of hydrolysis of PLA was well described using the Logistic model. The activation energy for the hydrolysis (Q) of PLA is 18.1 kcal∙mol−1 in the temperature range of 250–285°C. The results of this study provide important insights and crucial parameters for the production and application of PLA.