Study On Direct Synthesis Of Polylactic Acid, Preparation And Properties Of Polyvinyl Alcohol/Polylactic Acid Composites

Polylactic acid (PLA) has attracted much attention in medical and pharmaceutical applications owing to their wonderful biologic compatibility and biodegradability. Direct polycondensation is expected to have wide applications because of its shorter procedure and simpler process than ring-opening polymerization of lactide. However, their applications are sometimes interfered with the high hydrophobic property and a slow hydrolytic degradation rate. Thus, studies on the modification of PLA is important both theoretically and practically. This thesis includes two parts:1. In the study, lactic acid was used as the monomer, the syntheses of polylactic acid via melt polycondensation were investigated. The molecular weight influencing factors of PLA, such as temperature, time of polymerization, pressure, the kinds and quantities of catalyst were studied in details. The viscosity-average molecular weights of polymers were determined. Their structure was confirmed by IR. The compound catalyst SnOct₂/ toluene-p-sulfonic acid which has high activation was selected.The results showed that the optimum conditions of the polycondensation were that: reaction time 12h,reaction temperature 170℃,vacuum of 0-300 Pa, with SnOct₂ of 0.5% and toluene-p-sulfonic acid of 0.2%. High molecular-weight PLA (12400) can be gained by the direct melt polycondensation from lactic acid.2. On the view of material design, polyvinyl alcohol (PVA), with rich hydroxyl groups, was selected as the second component to improve the hydrophilit of PLA and accelerate its degradation. The blend film was obtained by solvent casting. The factors influencing properties of PLA/PVA composites, such as ratios of PLA and PVA , temperature, time, the kinds and quantities of co-solvent were studied in details. Moreover, the degradation properties of the film in normal saline etc. and the thermal degradation of PLA/PVA were also studied. At last, the structure, crystallizing property and degradable property of PLA/PVA were characterized by DSC, XRD, IR and SEMo The experiment results showed that DMSO is the best co-solvent for PLA and PVA, the hydropbilit and degradation rate of PLA/ PVA Composites were improved in different extent and could be adjusted by changing the compositions of the blends.