| Poly(lactic acid)(PLA) is a kind of aliphatic polyesters. As one of the completelydegradable environmental friendly materials, its raw material is lactic acid obtainedfrom fermentation of starch. Its mechnical characteristics are as excellent as popularplastics in use, in addition, after use, it can degrade into carbon dioxide and water innature, which avoids "White Pollution". In recent years, the demand of environmentalprotection has arisen people's attention on the study of poly(lactic acid), making it analternative of popular plastics and bringing a broader prospect to its applications.Using lactic acid as momer to prepare PLA, direct polymerization methodrequires a shorter flow, a simpler technology and a lower cost, having a broaderprospect compared with ring-opening polymerization. In this part the influences of itsreaction time and temperature, types and dosage of catalysts and concentration ofsolution on the molecular weight of poly(lactic acid) were investigated. In this study,the best process parameters to get higher molecular weight of PLA were listed asfollows: for every 100g lactic acid, 0.4g SnCl2 were added as catalyst; thepolymerization temperature was 140℃; the ratio of toluene to lactic acid is 4: 1; thepolymerization process lasted 25h. Chemical structure of PLA was characterized byFT-IR, 1H-NMR, and 13C-NMR. The DSC curves of PLA showed that its Tg was54.3℃and its Tm was 163.8℃, and its Xc was 13.9% indicating a higher thermalstability. In addition, the biodegradability of PLA was studied, showing that itsdegrading rate reached 74% in 12 weeks.The best process parameters of preparing lactide were that prepolymerizationtemperature was 160℃; prepolymerization process lasted 6h; depolymerizationtemperature was 220℃; depolymerization process lasted 2h; percentage of catalyst was2.0%; the highest production rate of lactide was 40.2%. When lactide was purified byethyl acetate for 4 times, it was pure enough to polymerize to be PLA.When preparing PLA by ring-opening polymerization of lactide, the best processparameters to get the highest molecular weight were that 0.04% Sn(Oct)2 as catalyst; the first stage temperature was 130℃and its reaction process lasted 1h, while thesecond stage temperature was 160℃and its reaction process lasted 12h. The DSCcurves of PLA showed that its Tg was 63.4℃and its Tm was 166.2℃, and its Tc was113.4℃。Photos of PLA by polarization microscope showed a sphere crystal.In order to obtain cheap and good physical and mechanical propertiesbiodegradable polyester materials, PETA was synthesized by direct and indirectpolymerization. The changes of biodegradation rate of different components of PETAare analyzed. PETA50 possesses the highest biodegradation rate. In alkali buffersolution, the biodegradation rate of PETA was the highest, which reached to 7.8% in50 days; in acid buffer solution it took second place, which reached to 6.4% in 50 days;in natural soil, it possessed the lowest biodegradation rate, which reached to 3.1% in50 days. The chemical structure of PETA was characterized by FT-IR. The thermalstability of PETA was characterized by TGA, which shows that with the increasegroups of lactic acid, its thermal stability declines.Toluene-p-sulfonic acid was chosen as catalyst in the synthesis of lactic acidglycol ester, the best dosage of which was 8% to lactic acid; the best ratio of alcohol toacid is 3:1; the appropriate reaction temperature ranged from 140 to 142℃; the bestester reaction time was 2h, the most appropriate dosage of dehydration reagent was30g. Drop-by-drop charging lactic acid to reaction system contributed to the increaseof production rate of lactic acid glycol ester. Average production rate of lactic acidglycol ester under best process parameters was 96.8%. The best process parameters ofsynthesizing lactic acid glycol ester testified by orthogonal test were that reactiontemperature was 140℃; reaction time was 2h; catalyst dosage 8%; ratio of lactic acidto glycol was 3:1. The orders of factors of production rate are listed by their influentialdegrees from the highest to the lowest as reaction temperature, ratio of raw materials,dosage of catalyst and reaction time. The boiling point of lactic acid glycol ester bydistillation was 225℃. Lactic acid glycol ester was characterized by FT-IR and1H-NMR.In this paper, the degradable rate and the change of molecular weight of differentratio polyblends PET/PLA that were prepared by solution blends were investigated.Experiment finds that the degradable rate of the membrane of PET/PLA (9:1) ishighest among others in the same situation; the highest degradable rate of the composites membranes occurred in base solutions; the order of molecular weight issimilar to the degradable rate. |
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