There are three major methods for the preparation of PLA polylactic acid

1. Direct polycondensation method (one-step method)

Direct condensation of lactic acid monomers is also known as one-step polymerization. In the presence of a dehydrating agent, the hydroxyl and carboxyl groups in the lactic acid molecule are dehydrated by heat and directly condensed into oligomers. A catalyst is added, the temperature continues to rise, and the low relative molecular weight of polylactic acid polymerizes into a higher relative molecular weight polylactic acid.

2. Two-step method

Lactic acid is used to form cyclic dimeric lactide, which is then opened and polycondensed into polylactic acid. This technology is relatively mature, and the main process is that the raw materials are fermented by microorganisms to obtain lactic acid, and then after refining, dehydration oligomerization, high-temperature cracking, and finally polymerization into polylactic acid.

3. Reaction extrusion to prepare high molecular weight polylactic acid

Polylactic acid with a molecular weight of 150,000 can be obtained by continuous melt polymerization experiments by combining batch stirring reactor and twin screw extruder. A twin-screw extruder is used to further polycondense the low molar mass of lactic acid prepolymer on the extruder to prepare a higher molar mass of polylactic acid.