Study On Synthesis Of Poly(Lactic Acid)

The poly(L-lactide)(PLLA) synthesis process has been studied in this paper. First ofall, lactic acid oligomer was gotten from lactic acid by direct melt polycondensation, whichwas going to prepare the PLLA by further chemical reaction. Influence factor of the reactioncondition was studied and also the structure and properties of productions were investigatedby means of FT-IR, DSC, TG, tensile test and contact angle measurement.(1) The optimal impurity-removing technology was obtained by studying the influenceof condition’s parameter on the impurity process with nitrogen protection then heating uplactic acid to100℃for40minat the rate of5℃/min. it can obtain82wt%lactic acid.(2) The purified lactic acid and stannous octoate/TSA were used as raw material andcomposite catalyst accordingly to synthetize lactic acid oligomer by direct meltpolycondensation. Via studying the reaction productions that were made from differentconditions and parameters, it can get the optimal reaction condition: the amount of stannousoctoate and TSA were both0.4wt%, reaction under180℃for8hunder nitrogenprotection can make the highest molecular weight of production.(3) The PLLA was synthesized from lactic acid oligomer which got from direct meltpolycondensation and stannous octoate/TSA by solid-state polycondensation. The optimalreaction condition and parameter was conclusive by studying the influence factors onproduction which is: lactic acid oligomer was first heat treatmented for2h at105℃, andthen reacting for20h at150℃. Molecular weight and melting point of PLLA werebothhigher than lactic acid oligomer.(4) Epoxy soybean oil (ESO) was reacted with lactic acid oligomer. Then I studied theinfluence of the amount of ESO, reaction temperature and time on production. Through thestudy, I can get the optimal reaction condition that is: when the mass fraction of ESO was4wt%with reacting for7h at150℃, the molecular weight of copolymer PLLA-ESO couldscore the highest value. Comparing with lactic acid oligomer, PLLA-ESO copolymer’sweight loss temperature and tensile strength were lower while the hydrophilicity propertyand elongation-at-break were increased.