INDUSTRIAL PRODUCTION OF HIGH‐MOLECULAR‐WEIGHT POLY(LACTIC ACID)

Polymers based on lactic acid (PLA) are the most promising category of polymers made from renewable resources. The properties of lactic-acid-based polymers vary to a large extent depending on the ratio between, and the distribution of, the two stereoisomers or other co monomers. From a chemistry point of view, lactic acid can form PLA by means of the reaction of the hydroxyl and carboxylic acid groups of lactic acid. The formation of lactide cannot be excluded, but to suppress the lactide formation and increase the first-pass yield of the polycondensation reaction of lactic acid, the lactide can be returned back to the reaction mixture. Traditional polycondensation catalysts are strong acids, and organometallic compounds are also commonly used catalysts. In azeotropic dehydration, the same principle stages as in direct melt condensation of lactic acid are present, with the exception that the last high viscosity melt-polycondensation stage is eliminated because the polycondensation is performed in solution.