Synthesis And Properties Of Poly-lactic Acid And Copolymers

The synthesis of PLA and PCLA copolymers by ring-openingpolymerization has been systematically studied. The structure and propertieshave been characterized by means of Fourier transform infrared spectrum(FTIR) , differential scanning calorimetry (DSC) , thermogravimetry(TG) , tensile test and degradation test. The investigation results show thatthe polymerization temperature, the pressure of system and thedepolymerization temperature have obviously affected the yield of lactides.At a certain temperature range, the yield of lactides increases with theincrease of polymerization temperature and the pressure. The increase ofdepolymerization temperature contributes to the increase of the yield oflactides. The maximum yields of L-lactide and DL-lactide are 35% and 24%respectively.The experiment results of ring-opening polymerization of lactides show that the amount of initiator, polymerization temperature and polymerization time are the key factors that affect the molecular weight of PLA. The molecular weight of PLA increases with the increase of initiator at first and then decreases with further increase of the amount of initiator and the optimization procedure of synthesis of PLA is that the mol ratio of the initiator and monomer is 1:8000, the polymerization temperature is 130℃and the polymerization time is 48h. The highest molecular weight of PLA is 28×10⁴. The results of FTIR verify the structure and the results of DSC and TG show that the glass transition temperature of PLA is 62℃, the crystallintity is 42.3% and the thermal decomposition temperature is 299℃.The copolymer can be synthesized by use of Sn (Oct)₂ as the initiator, and the chain structure of copolymer has also been characterized. The experimental results of HNMR show that the compositions of copolymers are close to the feed ratio. The DSC, POM and XRD results show that with the increase of theε-CL content, the glass transition temperature and crystallinity decreases and the PCLA60 is completely amorphous. The yield strength decreases while the elongation at break increases with theε-CL content increasing. The degradation test indicates that the mass loss increases with an increase of theε-CL content.