Study On Synthesis Of Poly(lactic Acid) By Melt Polycondensation And Modification Of PLA By In Situ Polymerization

Polylactic acid (PLA) has been the research focus of macromolecule chemistry with its wonderful biologic compatibility and biodegradable properties.The conventional produce of PLA is a ring-opening polymerization, but this method limits its widespread application because of the long route and the high cost. How to control the process route and reduce material costs are the main factors to expand the application of PLA. Using L-LA that resists heat as raw material, we studied on the synthesis of polylactic acid by low-cost technology to realize its widely applications.PLA prepared by direct melt polycondensation is still limited in applications due to its low molecular weight, intrinsic brittleness, and poor thermal stability. Accordingly, we study on the effect of triphenyl phosphite (TPPi) enhancing the intrinsic viscosity of PLA, and the modification of PLA by in situ polymerization process with the plant fibers that graft MAPP after alkali treatment as modifier. Expect for the costs of PLA are reduced, while the performance of PLA.are improved.First of all, the melt condensation polymerization conditions for the polylactic acid had been discussed such as types and dosage of catalysts, prepolymerization, the reaction time and temperature, TPPi, which was the fundamental theory for the preparation of the modification of PLA by in situ polymerization process with the plant fibers. After the optimum conditions of high molecular weight Poly(lactic acid)(PLA) polymers by melt polycondensation were confirmed, the modified and unmodified plant fibers were added to the reaction system behind the prepolymerization of lactic acid, then the polymerization conditions remain unchanged. Then several instruments such as infrared spectrum (IR), gel permeation chrom- atography (GPC), tensile testing machine, differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), scanning electron microscope(SEM) and so on had been employed in this study. The effect of the addition of modified and unmodified plant fibers and their content on the molecular weight and structure of polylactic acid and properties of the composites including mechanical properties, thermal properties and degradation properties was discussed. Besides, the color of the composites was investigated. The results showed that when the content of plant fibers modified with MAPP is 0.2%, the product's color was shallow, meanwhile, the properties of the product was superior. At the moment, the tensile strength, the elongation at break, the temperature of starting thermal-decomposition increased by 14.07%, 21.35%, 9.75% than pure PLA, respectively. But the impact strength reduced by 5.26%. According to study on the thermal and water degradation of product, the degradation character- istic of product decreased with the addition of modified plant fibers. Whereas the ma- terial's vicat softening temperature is approximately 38℃, it could be used as the fixed material of bone fracture.