Study On The Preparation Of Polylactic Through Solution Polycondensation

Polylactic is one kind of biodegradable polymer materials with renewable resources such as corn starch as its raw materials. Polylactide has many outstanding properties including non-toxic, non-irritative, excellent biocompatibility, high bioabsorption, biodegradability and also has excellent physical and mechanical properties.In this paper, the D, L-lactic acid was choosed as monomer to synthesis the polylactic acid through the method of direct polymerization method. This method could greatly simplify the preparation technology and shorten the preparation period of polylactic acid.As the monomer, the D, L-lactic acid was firstly treated by the process of pre-dehydration. Some influence factors during this process, such as the drying time, temperature, pressure and vacuum dehydration, were carefully investigated and the optimal parameters were obtained as follow: first decompression dehydration to lactic acid temperature under 80℃, the process of vacuum is keeping -0.03MPa ,by this way we can make the emergence of lactic acid monomer is completely free of water, and provides favorable conditions for the next lactic acid directly polymerization process.Based on the above experimental results, some other influencing factors on the molecular weight and the color of polylactic acid products were also discussed, which including the selection and dosage of solvent, the catalyst type and dosage, the time needed for polymerization, polymerization temperature, the system, the polymerization reaction system, vacuum polymerization late molecular sieve dehydration and the reaction atmosphere.The optimal parameter on the synthesis of polylactic acid was as follow: the polymerization catalysts is no ferrie sulfate-potassium thiosulfate, the amount of lactic acid is monomer 25 % of its weight, polymerization time is for 24h, the polymerization temperature is 160 degree and the polymerization vacuum - 0.09 MPa. According to the best technological conditions for the synthesis of polylactic acid, the viscosity average molecular weight of polylactic was near 20,000. Through the polymer products of infrared spectrum analysis, proofing the synthetic products is polylactic.