聚乳酸的合成及其热降解性研究

Study of synthesis and thermal degradation on polylactic acid

以L-乳酸为原料,通过预聚合和固相聚合合成了聚乳酸,并研究了其热降解性.实验结果表明：（1）预聚合的反应温度180℃,反应时间8h,采用复合催化剂,总用量在0.5%～0.7%之间;反应压强1000Pa,预聚物重均分子量在5000左右,熔点145℃～150℃.（2）固相聚合反应温度低于预聚物熔点5℃,时间30 h,可得重均分子量13.765万的聚乳酸.（3）聚乳酸产品干燥时间4h,熔融温度180℃,熔融时间20min,抗氧剂用量0.3%时,聚乳酸的降解率最小约为40%.

Polylactic acid was synthesized by pre-polymerization and solid- polymerization,and its thermal degradation was studied. The experiment results show that （1）The reacting temperature is 180℃,reacting time is 8h, using composite catalysts which total dosage is 0. 5% -0. 7%, reacting pressure is 1000Pa, the prepolymer molecular weight is about 5 000, and melting point is 145℃ - 150℃. （2）In solid- polymerization state,the reacting time is 30 h, the reacting temperature is 5℃ lower than prepolymer melting point, the polylactic acid whose molecular weight is 137 650 can be obtained. （3）The thermal degradation of polylactic acid is as follows ： the dry time is 4h, the melting temperature is 180℃, the melting time is 20 min, the antioxidant is 0.3%, the lowest rate of thermal degradation is about 40%.