Monomer preparation The monomer is mainly fermented by glucose in lactic acid bacteria.
Polymerization method of polylactic acid
Polylactic acid has two synthetic methods, namely, the open loop polymerization of lactide (the cyclic dimer of lactic acid) and the direct polymerization of lactic acid. One is decompression in the solvent by direct polymerization of lactic acid, namely: lactic acid → prepolymer → polylactic acid, direct polycondensation of lactic acid by the refined lactic acid polymerization directly, is the earliest and simplest method.
The process of the method is simple, but the molecular weight of the polymers is low, the molecular weight distribution is wide, and the processing performance of the polymer is not enough to meet the needs of the fiber-forming polymers, and the polymerization reaction is more than 180C, the polymers are easily oxidized and coloured, and the application is limited. Another method is under normal pressure with cyclic polylactic acid as raw material polymerization (lactide open loop polymerization), namely: lactic acid → prepolymer → ring dimer → polylactic acid. The production process of lactide open loop polymerization is as follows: first, the lactic acid dehydration is made into lactide, and the lactide is prepared by cyclic polymerization. The process and purification of lactic acid is the key and difficult point of preparing lactide, which can be used to get high molecular weight polylactic acid and to meet the requirements of fiber-forming polymers and bone fixation materials.