目的 研究PLA在酸性条件下降解及其机理。方法 通过在酸性水溶液中降解不同时间， 得到一系列不同相对分子质量的PLA， 利用黏度法、 凝胶色谱以及红外光谱对PLA的降解机理进行研究。结果 PLA的数均分子量随降解时间的增加逐渐减小， 失重率和降解率逐渐升高， 在降解23 d后， 产物的数均分子量从4050降至2490， 失重率从9.9%升至75.1%， 降解率从98.3%提高至99.0%。降解过程中， PLA的相对分子质量分布系数基本保持不变， 一直维持在1.25左右。结论 在降解过程中， 酯键的断裂是PLA初步降解的主要方式， H+浓度的升高有利于催化酯键的断裂， 加剧PLA降解。

Objective To study the acid degradation of PLA and to investigate its mechanism. Methods A series of PLA with different molecular weights were obtained after different degradation time in acidic aqueous solution, followed by viscometric determination, GPC and FTIR to analyze its degradation mechanism. Results The number-average molecular weight of PLA gradually decreased with the increasing degradation time, while the weight-loss rate and degradation rate gradually increased. After 23 d degradation, the number-average molecular weight of PLA diminished from 4050 to 2490, while the weight-loss rate and degradation rate accumulated from 9.9% and 98.3% to 75.1% and 99.0%, respectively. The molecular weight distribution coefficient remained stable at about 1.25 during the degradation. Conclusion The main initial degradation of PLA was the fracture of ester bond, which was accelerated by the concentration enhancement of H+. As a result, degradation of PLA was exacerbated.