Dissertation
Dissertation > Industrial Technology > Chemical Industry > Synthetic resins and plastics industry > General issues > Basic theory

Research on Synthesis Process of Polylactic Acid

Author YouXinQiang
Tutor WeiShunAn
School Chongqing University
Course Chemical Engineering and Technology
Keywords Lactide Polylactic Acid High-yield technology Synthesis process Technology discussion and optimization
CLC TQ320.1
Type Master's thesis
Year 2012
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Polylactic Acid (PLA) is a kind of environmental friendly high molecular material,which has been extensively studied and applied because of its favorablebiodegradability and biocompatibility. But in the preparation process of PLA,there areproblems such as low production rate and purification difficulty of lactide,lowmolecular weight of PLA,which restricts the industrialization process of PLA. Theresearch status at home and abroad,and preparation method has been illustrated in thethesis. Based on the ring-open polymerization method of lactide,the process parameters arestudied and optimized systematacially at the following two sections: the increasement oflactide production rate and the preparation of high molecular PLA.In the first section,the preparation technology of lactide which used zinc oxide asthe catalyst and L-lactic acid (technical grade) as the raw material was studied andoptimized in this study on the catalyst dosage, polymerization temperature,polymerization time and agitator speed who significantly influence the yield of lactide.The final experiments witness that: catalyst dosage0.75%wt, polymerizationtemperature range170℃~230℃,polymerization time3.5h and agitator speed range300rpm~600rpm. The experiment results,of which the qualitative analysis wasconducted by gas chromatograph and trace water monitor,showed that the yield of rawlactide could steadily achieve82.95%from72.4%. The melting point and molecularstructure of lactide after4times recrystallization with ethyl acetate as solvent wascharacterized by differential thermal analysis and infrared spectrometer.In the second section,the synthesis process of PLA which was prepared byblending of L-lactide and D,L-lactide was studied. The effects of the content of D,L-lactide,catalyst dosage,polymerization temperature,polymerization time andvacuum degree on the viscosity average molecular weight (Mv) of PLA wereinvestigated respectively. The final outcome is that: content of D,L-lactide25%wt,catalyst dosage0.1%,polymerization temperature150℃,polymerization time22hand vacuum degree-0.096MPa. The weight average molecular weight (Mw) of PLAreached1.15×105by GPC. And the molecular structure and thermal property of PLAwas characterized by infrared spectrometer and differential thermal-thermal gravitationanalysis.Through the experiment and characterization of products,not only the production rate of lactide is increased gradually,but also the feasibility of PLA prepared by twokinds of lactides and the effect of mixing ration on the molecular of PLA,usefulexploration is made for the industrialization of PLA.

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