Polylactic Acid Synthesis Process

Polylactic acid(PLA), a kind of aliphatic polyesters, bears wonderful biologic compatibility and biodegradable properties. PLA that can finally biodegrade into CO2 and H2O under the influence of microorganism, water, acid or alkali is harmless and non-toxic to the environment. As a thermoplastic polymer, the mechanical properties of PLA are between PS and PET, easy to be processed and molded in many methods. Processing equipment of general plastics, such as equipment for extrusion, injection and blow molding also suit for PLA. More using can be achieved by blended or co-polymerization with other general plastics. Besides, PLA can be processed by melt-spinning process. The fiber can be dyed easily. So the use of PLA will be very widely. The research of PLA will benefit economy and society.In this dissertation, D,L-lactic acid made in china is as raw material. Polymerization methods of PLA, including ring-opening polymerization of lactide, solution polymerization and melt polymerization of lactic acid, were studied systematically. This thesis includes two parts.(1) Two methods of direct polymerization of PLA were studied under low vacuum. The molecular weight influences of PLA, such as temperature, quantity of catalyst, time of polymerization and the kind of catalyst were discussed. IR, 'H-NMR and 13C-NMR were used to conform the structure of PLA.(2) Study the synthesis of lactide. The influences of quantity of catalyst, temperature, vacuum tightness, time of degradation on the yield of lactide were discussed. Then, synthesis of PLA used lactide as material. The influences of quantity of catalyst, temperature, time ofpolymerization on the molecular weight of lactide were also discussed.The products were characterized by IR, GPC, 'H-NMR, 13C-NMR, DSC.This thesis study the mechanism of synthesis lactide used D,L-lactic acid.The method of purification was reformed. The time of crystal was decreasedfrom four to three.This thesis reformed the method of pressurizer. It was confirmed that increased molecular weight of PLA and inhabited subsidiary reactions.