PLA corn starch polylactic acid formation process video
Preparation method of polylactic acid
1) Direct polycondensation method
Polycondensation is the direct condensation of lactic acid monomers, 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 to form oligomers. Add the catalyst, continue to raise the temperature, and the polylactic acid with low relative molecular weight is polymerized into polylactic acid with higher relative molecular weight.
2) Two-step method
Lactic acid is made into cyclic dimer lactide, and then ring-opening polycondensation into polylactic acid. This technology is relatively mature, and the process of polylactic acid produced by NatureWorks in the United States is the process. The polylactic acid production technology jointly developed by China's Hisun and the Chinese Academy of Sciences is similar. The main process is that the raw material is fermented by microorganisms to obtain lactic acid, and then undergoes refining, dehydration oligomerization, high-temperature cracking, and finally polymerizes into polylactic acid.
3) Preparation of high molecular weight polylactic acid by reactive extrusion
Combining batch stirring reactor and twin-screw extruder for continuous melt polymerization experiments, polylactic acid with a molecular weight of 150,000 can be obtained from lactic acid through continuous melt polycondensation. A twin-screw extruder is used to further polycondense the low molar mass lactic acid prepolymer on the extruder to prepare higher molar mass polylactic acid. When the reaction temperature is 150°C, the amount of catalyst is 0.5%, and the screw speed is 75 r/min, the molar mass of polylactic acid can be quickly and effectively increased by the twin-screw reaction extrusion polycondensation method, and the dispersion coefficient of the reaction extrusion product is reduced. Uniformity improved. Through the comparison of DSC curves, it is found that the crystallinity of polylactic acid prepared by reactive extrusion polycondensation method is reduced, which is beneficial to improve the brittleness of polylactic acid materials during use.