polylactic acid lactic acid method

⑴ direct polycondensation
Polycondensation is to direct condensation of lactic acid monomer, also called polymerization step. The presence of a dehydrating agent, lactic acid molecules in the hydroxyl and carboxyl groups heat dehydration, direct polycondensation oligomers. Adding a catalyst, lactic acid powder, low molecular weight polylactic acid polymer with a higher molecular weight of polylactic acid.
⑵ two-step
The cyclic dimer of lactic acid lactide, and then into a ring-opening polycondensation polylactic acid. This technology is more mature, the U.S. company NatureWorks polylactic acid production process is the process technology. China Sea being developed jointly with the Chinese Academy of polylactic acid production technology calcium lactate, the main process raw materials by microbial fermentation of lactic acid, and then after purification, dehydration oligomeric, pyrolysis, and finally aggregated into polylactic acid.
⑶ reactive extrusion prepare high molecular weight polylactic acid
A batch-type stirred reactor and a twin-screw extruder combined continuous melt polymerization experiments, obtained from a lactic acid obtained by the continuous melt-polycondensation of the molecular weight of polylactic acid 150000. Twin-screw extruder of the low molar mass of lactic acid prepolymer further condensation in an extruder to prepare a high molar mass of the polylactic acid. The reaction temperature is 150 ℃, the amount of catalyst was 0.5%, a screw speed of 75 r / min when the double-screw extruder polycondensation reaction rapidly and effectively increase the molar mass of the polylactic acid, and the reaction product was dispersed reduced coefficient of extrusion, uniformity better. The DSC curve by comparison, obtained by reactive extrusion of the polylactic acid polycondensation process crystallinity decreased, polylactic acid material which is to improve the performance in the course of a greater brittleness is beneficial.