Study On New Techniques Of Synthesizing Lactide

Polylactide has attracted much attention due to its biodegradability, bioenvironmental compatibility and excellent mechanical properties. However, its applications is restricted by its high price. Since lactide is an indispensable material to prepare polylactide, reducing its cost will greatly extend application range of polylactide. To avoid the high cost in purifying lactic acid, lactide was prepared directly in the thesis from ethyl lactate and ammonium lactate, which are intermediate products in the manufacture of lactic acid. Therefore, the production technique of polylactide is simplified and the cost is reduced. Reaction dynamics of ethyl lactate was investigated first in this paper. The results show that polycondensation reaction of ethyl lactate obey second-order reaction kinetics and the nitrogen can prevent oxidation and drive the reaction to the right direction. It was also found that the yield of lactide was affected by catalyst system, flow rate of nitrogen, reaction temperature, oligomerization time and molecular weight of oligomers. The optimum conditions were obtained finally.Secondly, a lot of probes have been done to prepare lactide from ammonium lactate. The obtained results were as follows: (1) Ammonium lactate decomposition, which produces lactamide and water can't be ignored in the reaction. (2) Pretreatment procedure of total reflux was essential to attain successful reaction. (3) The use of rectification and nitrogen help ammonia to be separated from reaction system. (4) The added water can greatly improve the yield of lactide. A laboratory-scale reaction devices were chosen after a series of comparisons.Finally, the structure of lactide was characterized and the solvent effects on the recrystallization were compared between ethyl acetate and acetone. Some exploring experiments were carried out and a stable, accurate and highly sensitive HPLC method was constructed for quantitative analysis of lactide and ethyl lactate. The wide linear range, rapid analysis and good recurrence gave satisfying results about quantitative measurement of actual samples.