摘要
聚乳酸是一种具有优良的生物相容性和可生物降解性的聚合物，随着高分子材料聚乳酸及其共聚物在生物材料领域，特别是作为组织工程支架材料、药物释放材料和骨折内固定件的应用日益广泛，其研制与开发日益受到人们的重视，同时聚合单体丙交酯也越来越受到重视。长期以来丙交酯的成本一直是制约聚乳酸推广应用的最重要的因素之一，本文致力于设计出一套能最大限度降低丙交酯成本的工艺过程，并对丙交酯聚合过程中影响聚乳酸分子量的因素进行了初步探讨。可以相信，聚乳酸一旦工业化，它在医用材料和降解塑料方面将有难以估量的应用前景。
本文在总结了目前众多聚乳酸单体——丙交酯的合成技术的基础上，选用减压蒸馏工艺并加以改进，设计出最佳的实验装置，使丙交酯的产率从30％提高到45％，并对重结晶后的母液进行有效的回收，回收率也能达到40％，对回收后的丙交酯进行了测试分析，证明了回收过程的可行性。
首先，从改善合成丙交酯反应的条件入手，通过对丙交酯合成反应的机理分析，对反应过程中催化剂用量、种类、脱水温度、时间、压力、解聚温度、时间、压力等做了详细的研究，得出最佳的合成条件和工艺过程。脱水温度，140℃；脱水时间，4小时，使脱水量达到94％左右；解聚温度，240℃；解聚时间，2小时；终止温度，270℃。
其次，回收重结晶母液使损失在乙酸乙酯中的丙交酯得到循环利用，对回收工艺过程进行了周密分析和探讨，并比较了以上两种过程的异同。
然后，用甲醇钠非水滴定法测定丙交酯中残存乳酸，卡尔-费休法测定丙交酯中残存水的含量，用提勒管测定精制丙交酯熔点，用红外吸收光谱、紫外光谱、差热分析对合成的丙交酯以及回收的丙交酯进行表征。结果表明重结晶三次后丙交酯纯度在99.5％以上。
最后，对精制后的丙交酯本体开环熔融聚合过程进行分析，对反应过程中聚合温度、聚合时间以及引发剂用量做了详细研究，并对PDLLA的性能进行多种测试分析，证明工艺过程是可行的。
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 of
PLA and synthesis of its monomer-lactide are catching more attention in this
field. 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 processa
above 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.
引文
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