Synthesis、Modification And Properties Study Of High Molecular Weight Poly Lactic Acid

Poly lactic acid(PLA) has attracted much attention due to its advantage such as biodegradable, biocompatibility, renewable and so on. This thesis studies the process of synthesis high weight molecular PLA for the problems of the process of synthesis PLA in the current by direct polymerization and lactide ring-opening polymerization. And some progress has been achieved.High molecular weight PLA was synthesized successfully via dehydration gradually melt polycondensation method from 80 wt% industrial L-lactic acid by using Stannous caprylate/Stannous chloride/p-toluene sulfonic acid as composite catalyst, and in the presence of molecular sieves type 5A as dehydrating agent. It found that the specific rotation and the molecular weight slowly increase first then decreased if long time recation, and with the molecular weight increase that the glass-transition, the starting and ending temperature increased first then decreased slowly and weeny dipping and heaving tendency. A high-quality polymer of PLA can be obtained in optimum process condition and its weight-average molecular weight exceeds 1.6×105 which is with the advantages of lighter color, short reaction time, low cost, simple preparation technology and narrow molecular weight distribution.80 wt% L-lactic acid as raw materials, stannous caprylate as the catalyst, the lactide ring-opening polymerization and got sticky average molecular weight 5.1×105 of PLA.Obtained the optimum technological conditions for synthesis of lactide, its yield up to76.7%. Researched synthetic optimum process conditions for the synthesis of high molecular weight PLA. Fourier transform infrared spectrum characterization and analysis of the synthesis of lactide and poly lactic acid. Analyzed by DSC and TG in differenttimes for the purification of the purity of lactide, the results demonstrate that the purity is higher after the three times for the purification of lactide. And analyzed under the different synthesis temperature synthesis of poly lactic acid too. Suggests that synthetic poly lactic acid is good under 130 ℃ heat stability. The degree of crystallinity of PLLA is biggest when polycondensation temperature at 140 ℃ and crystallite size is largest at130 ℃ that were characterized via by X-ray Diffraction(X-RD). its sticky average molecular weight exceeds 5.1×105 which is with advantage of high molecular, narrow molecular weight distribution, short reaction time, high yield, and low cost.88 wt% L-lactic acid as raw materials, Sulfamic acid/stannous caprylate as the catalyst, triphenyl phosphite(TPP) as antioxidants and the reagent of promote polymerization, via by microwave radiation synthesis weight-average molecular weight2.95 × 104 and molecular weight distribution 1.19(Mw/Mn) of heat-resistant PLA.Studied the impact factors of catalyst dosage, temperature and reaction time on the synthesis high molecular weight PLA. It is concluded that the initial degradation temperature increased about 100 ℃ after adding antioxidants and no other functional groups are lead up. With reaction time or temperature increased, yield and specific rotation gradually reduced. These research provides the experimental basis for low cost prepared high molecular weight and narrow molecular weight distribution PLA. Not only have certain academic significance, but it has potential application value.Graphene oxide(GO) was prepared by Hummers method, and then graphene oxide is grafted by poly lactic acid. With graphene oxide and grafted graphene oxide are blended with poly lactic acid solution respectively, and their solvent was volatile into film at house temperature. The late stage was studied by UV light on the degradation of poly lactic acid in two different samples. Showed that the grafted graphene oxide and poly lactic acid blend samples with good mechanical properties, but its hydrophilicity,inhibit photocatalytic degradation are worse than graphene oxide and poly(lactic acid)blends samples.