基于乳酸水溶液循环的聚乳酸水热解聚行为研究

Study on Hydrothermal Depolymerization of Polylactic Acid Based on Circulation of Aqueous Lactic Acid Solution

研究了聚乳酸(PLA)在180℃高温循环水热条件下的降解过程,分别采用质量变化、高效液相色谱(HPLC)测试、热失重分析(TG)、傅里叶变换红外光谱技术(FTIR)以及液相色谱-质谱联用仪(LC-MS)等比较了不同循环水热过程中PLA样品的质量损失、乳酸的生成、PLA材料的热失重过程以及化学结构的变化过程。结果表明,循环次数越多,PLA样品的失重过程越快,失重过程在180℃水热反应的40 min内完成;乳酸的生成速率随着循环次数的增多而加快,但最终产量基本相同,化学循环过程没有降低PLA的转化率,具有循环稳定性;随着水热过程的进行,水解后的PLA样品的稳定性增强,且循环次数越多,稳定性的增强速率越快;在水热过程中,PLA样品的羟基指数和羰基指数都呈不断增大的趋势,且增大速率随循环次数的增多而加快,即化学循环过程加速了PLA的水解降解。

The degradation behavior of poly(lactic acid)(PLA)was investigated at a high temperature of 180 °C under the circulating hydrothermal condition,and their weight variation,generation of lactic acid,thermal weight-loss process,and chemical structure were evaluated by mass-loss rate,high performance liquid chromatography,thermogravimetric analysis,Fourier-transform infrared spectroscopy and liquid chromatography-mass spectrometry. The results indicated that the greater the cycle number,the faster the weight loss of PLA. The weight loss process was completed within 40 minutes by a hydrothermal reaction at 180 ° C. The production rate of lactic acid was accelerated with an increase of cycle number,but there was almost no variation in final volume. The PLA conversion rate was not reduced by the chemical cycling process,indicating a good cycle stability. The stability of PLA was enhanced with the progress of hydrothermal process,and the more cycles resulted in a much better stability. In the hydrothermal process,the hydroxyl index and carbonyl index of PLA exhibited an increasing trend with an increase of cycle number,suggesting that the chemical cycle process could accelerate the degradation of PLA.