The Synthesis Of High Molercular PDLLA

Polylactide is one of polymer materials that have good biocompatibility and no poisonousness can be degraded by organisms. The application of Polylactide and its copolymers is increasing in the fields of biomaterial, especially in the tissue engineering as scaffold material, carrier for pharmaceutical release and internal fixation of bone fracture. The development ofPLA and synthesis of its monomer-lactide are catching more attention in thisfield. The cost of lactide is one of the most important factors that hamper the PLA from widely use for a long time. In this paper a series of apparatus which can boost the product ratio to the utmost was focused on. Meanwhile the factors affecting the molecular weight of PLA in the polymerization were also discussed. Once the manufacture of polylactide is industrialized, it can be of wide application in the fields of medicine materials and degraded plastics without a doublt.This apparatus was designed based on summarizing the most synthetic processes of lactide presently. The reduced pressure distillation was choosed and improved to obtain lactide with high product ratio. The product ratio was increased to 45% from 30%. Furthermore, lactide was recycled from the ethyl acetate recrystallization solution, and structure was investigated with IR and UV spectrum. The result indicated that the process is suitable and feasible, and the product ratio is beyond 40%.Firstly, through analysis for the synthetic mechanism of lactide and according to improve the condition of synthetic process the factors related were studied in detail. These factors included the amount of activator, temperature and time of dehydration, temperature and time of depolymerization, pressure of the vessel et al. The optimal synthetic condition and process engineering were draw ultimately. The optimal dehydration temperature is 140℃, dehydration time is 4 hours, dehydration amount reach 94%, depolymerization temperature is 240℃, depolymerization time is 2 hours and finish at 270℃.Secondly, the recover of lactide from the ethyl acetate recrystallization solution reutilized the waste solution and heighten the general product ratio. The recovery process was analyzed and studied carefully. Moreover the two processaabove were compared in different aspects.Afterwards, the remnant lactic acid in lactide was measured by non-aqueous titration with sodium methoxide and the remnant water was surveyed by Karl-Fisher method. The melting point was investigated by Thiele tube and the characteristics of lactide were analyzed by IR, UV spectrum,TG and DSC respectively. The result indicated the purity of lactide which had been recrystallized thrice can reach 99.5%.Finally, the process of ring-opening polymerization of cyclic dilactides which has been purified was analyzed. The main factors which may affect the molecular weight of polylactide were studied in detail. The performance of PDLLA was investigated comprehensively. The results prove that the process is feasible.