Study On The Preparation Of Green Polylactic Acid And Its Modification Material

As a green material, poly lactic acid (PLA) and its modification pruducts have attracted much attention due to its renewability, fully degradability, good biocompatibility and processibility. PLA can be modified by other materials to obtain products with good performance for different applications. So PLA and its modification products can be considered as a substitute for universal material which has the most probability of industrial prospect.There are two ways to synthesize PLA: one is the direct polymerization, the other is ring-opening polymerization. Currently the main produce of PLA is synthesized through ring-opening polymerization. But this whole process is quite complex, and the intermediate of the reaction, lactide needs to be very pure, leading to the higher cost of producing PLA. Moreover, the wide applications are restricted by its poor elasticity. Many researches are focused on the direct polymerization of PLA nowadays, but satisfactory result has not been achieved. The direct polymerization of PLA mainly includes the following four methods: the melt polycondensation, the melt/solid polycondensation, solution polymerization and the chain-extending polymerization. This research mainly includes the synthesis of PLA through melt polycondensation, chain-extending polymerization and the preparation of poly urethanes(PUs) based on PLA which are modified by castor oil. A series of poly urethanes based on PLA modified by castor oil have been successfully prepared, they have different performance and has promising applications in different areas.The main content and conclusions are divided into four parts. In the first part, PLA with high molecular weight, Mw=5.6×104, was synthesized by melt polycondensation, when the amount of SnCl2·2H2O is 0.6wt% and the SnCl2·2H2O/TSA=1(molar ratio). In the second part, PLA with high molecular weight was used as a raw material, HDI as a chain-extending reagent, PUs based on PLA modified by castor oil were obtained through bulk polymerization. The results indicate that the inherent viscosity of PUs first decrease then increase with the increase of castor oil. In the third part, PLA with low molecular weight was modified by castor oil through solution polymerization, and TDI or MDI were used as a chain-extending reagents. By measuring the inherent viscosity, the inherent viscosity of PUs is very low. The fourth part includes two steps. At first, hydroxyl terminated lactic acid prepolymers have been prepared by the melt polycondensation of lactic acid and 1, 4-butanediol; then, the prepolymers are modified by castor oil through solution polymerization to obtain poly urethanes based on PLA modified by castor oil, and HDI used as the chain-extending reagent. The highest tensile strength of the PUs film is 31.2MPa, or the highest elongation at break of the PUs film is 176%. PUs with different performances can be adjusted.