Synthesis Of Lactide And Poly(D, L-Lactide) From Lactic Acid Oligomers In The Processing Fluents

PLA(Poly Lactide) was a kind of wildly used synthetical material with wonderful biologic compatibility and biodegradable properties. When finally degradated,it become CO2 and H2O, which were harmless and non-toxic to environment. As advanced material, PLA can be wildly used in many field like agriculture, commodity chemistry and biomedicine.The raw material of PLA is Lactic acid, which obtained from starch with fermentation. The Lactide ring-opening polymerization is the most important way to produce PLA, which obtain high molecular weight product. The quality and the price of Lactide influence the final result.In this paper, synthesis of lactide from oligomer was discussed. Usually, the lactide synthesized from fresh lactic acid. But a lot of oligomer left after reactivity, which can be reused when finally hydrolyzed. This dissertation focused on the investigation of the hydrolyzing conduction and composition of oligomer, especially the rudimental catalyst, which was excessive because of reactivity cumulating. The best technical method of increasing the rate of product and reducing the acid content was investigated by means of orthodoxical experiment. The results showed the amount of catalyst was the only prominent factor that influenced the rate of the product and the acid amount in the experiment. The optimums of the reactivity condition was proved that the extra catalyst was 0.7%, the dehydration time was 2h, the proportion of fresh lactic acid and the oligomer was 2:1.The condition was tested in the production equipment, the acid amount reduced to 12.1%,which was close to the result of fresh lactic acid reaction system. In the end, the lactide produced from oligomer polymerized to poly(D,L-lactide), which was characterized by IR spectrum, TG and DSC. The structure of lactide and poly(D,L-lactide) produced from fresh lactic acid and oligomer were proved to be the same.