Polylactic Acid Synthesis Process

In this dissertation, the synthetic processes of polylactic acid (PLA) by ring-opening polymerization of lactide were studied. High purity with high yield lactide was prepared by optimal technological conditions of the prepartion of lactide, and then the preparation process of PLA by ring-opening polymerization of lactide made in lab was studied.For the study of preparing the lactide, the optimal technological conditions of preparing high purity with high yield lactide were researched. The suitable molecular weight of oligomeric lactic acid was studied by controlling the time of dehydration and the amount of catalyst.Then the optimal experiment was carried out for obtaining the best technological conditions. Results showed that under the optimal conditions such as using 3.0mL Sn(Oct)2 as catalyst, initial decomposing temperature 150℃, dehydration temperature 180℃,7mL glycerol as diluent and ultimate decomposing temperature 250℃, the highest yield of crude lactide reached 85.7%. Results showed that the yield of lactide reached 64.8% when Ethanol used as solvent, and its melting point ranged from 127.4℃to 128.3℃after three times of recrystallization.For the study of ring-opening polymerization of lactide to synthesize PLA, the catalyst system was purified by using the method of vacuum distillation, Then the optimal experiment was carried out for obtaining the best technological conditions:the ampoules as the reaction vessel, n(M):n(I)= 6000:1, the reaction was temperature 130℃, reaction time was 48h, the intrinsic viscosity of the product was 2.31dL/g, and the relative molecular mass was 316,000, (using chloroform as solvent, Ubbelohde viscometer measurement, (25.0±0.1)℃, [η]=2.21×10-4Mv0.77). In order to simulate industrial production, the industrial nitrogen was used to instead the high vacuum. The results showed that molecular weight can be up to 288,000.It could be a good direction for the industrial production.