| In this dissertation, the technologic conditions of the preparation of PLA were studied. Lactide was prepared firstly. Using the lactide as raw material, the ring-opening of lactide to preparing PLA polymerization was researched.During the study of synthesing PLA by an indirect method, the lactide was synthesized by using of industrial monomer D,L-lactic acid. Taking the yield of product as an assessing standard, the orthogonal experiment was carried out for obtaining the best technological condition. Results were under the condition of mass fraction to lactic acid of Sn(Oct)2 4%, dehydration temperature 180℃, decomposing temperature 285℃, the highest yield of lactide reaching 84.6%. The yield of lactide reached 68.8% after recrystalization for one time, and its melting point ranged from 95.0℃ to 96.2℃. The yield of lactide reached to 59.2% and its melting point ranged from 125.2℃ to 126.5℃ after quintic recrystallization.During the studying of ring-opening polymerization of lactide to prepare PLA, the PLA was synthesized by using lactide prepared, and the technologic conditions of the synthesicing PLA were investigated. Taking the relative molecular weight of product as an assessing standard, the better technological conditions of synthesicing PLA were found through experiments. When ZnO was used as a catalysis, the technologic conditions were: mass fraction to lactide of ZnO 8%o, vacuum tightness 0.09MPa, polymeric temperature 170±5℃, polymeric time 7h, and the relative molecular weight of the synthesized PLA reaching 240,000. When Sn(Oct)2 was used as a catalysis, the technologic conditions were: mass fraction to lactide of Sn(Oct)2 3%, vacuum tightness 0.10MPa, polymeric temperature 170±5℃, polymeric time 7h, and the relative molecular weight of the synthesized PLA reaching 235,000. Finally IR and NMR were used to characterizing the products. |
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