The Study On The Synthesis Of L-Lactide

Poly(L-lactic acid)(PLLA); a kind of synthetical aliphatic polyesters, bears wonderful biologic compatibility and biodegradable properties, which is harmless and non-toxic to the environment as it can finally biodegrade into CO2 and H2O. Its raw material resource is L-lactic acid obtained from starch with fermentation. It has been used as one of the most important biomedical materials. At the same time, with physical mechanical properties similar to popular plastics, PLLA can substitute for them. Poly(L-lactic acid) will become an industrial material with considerable perspective. In this dissertation, the material of PLLA's polymerization, L-lactide was discussed.In this paper, L-lactide was synthesized by reduced pressure method. It included the synthesis of L-lactide, the purification of L-lactide and the L-lactide's analysis et. al.First, the paper studied the synthesis of L-lactide under reduced pressure . It showed that the results under reduced pressure were better . Its highest yield was up to 71.30% and the needed time was shorter. At the same time, the paper also studied the effects of the pressure , the temperature , the sort of catalyst and the catalyst concentration on the result . It showed that high vacuum can give high yield and in all used catalyst, ZnO was the best, and the temperature must be below 240Then, the paper studied the purification of crude L-lactide . Recrystallization and filter under reduced pressure were used . But they were unfit. The method which was based on the different physical properties of every component to purify the crude L-lactide was effective. The product was a colorless needle crystal. Its melting point was 95-96 and its optical purity satified need. Finally, the purified L-lactide was mensurated , the data accorded with the document.All of above results show, the L-lactic acid was initiated by ZnO under high vacuum to dehydrate and polymerize at 130~140 including the mensuration of L-lactide's melting point , L-lactide in 1 hour, and to decompose at 230~240 in 1.5 hours. Then it can give high yield.