Polylactic acid production is based on lactic acid as raw material, the traditional lactic acid fermentation mostly used starch raw materials, the United States, France, Japan and other countries have developed agricultural and sideline products to produce lactic acid fermentation, and then production of polylactic acid.
The production process of polylactic acid from lactic acid is: method
⑴ Direct Condensation method Condensation method is the direct condensation of lactic acid monomer, also known as one-step polymerization method. In the presence of the dehydrating agent, the hydroxyl group and the carboxyl group are dehydrated by heat and directly shrink into the low polymer.
By adding the catalyst, the low molecular weight polylactic acid is polymerized into a higher relative molecular mass polylactic acid.
⑵ Two Step The lactic acid is formed by the cyclic dimer lactide, and then the polycondensation is condensed into polylactic acid. This technology is more mature, the United States NatureWorks Company to produce polylactic acid technology is the process.
China's sea is jointly developed with the Chinese Academy of Sciences Polylactic acid production technology is similar to this, the main process is the raw material by microbial fermentation of lactic acid, and then after refining, dehydration low poly, high-temperature pyrolysis, the final polymerization of Chengzu lactate.
Preparation of high molecular weight polylactic acid by ⑶ reaction extrusion By using the combination of intermittent stirring reactor and twin-screw extruder, a continuous melting polymerization experiment is carried out to obtain polylactic acid, which is made of 150000 molecular weight by continuous melting polycondensation. A high molar mass of polylactic acid was prepared by using a twin-screw extruder to further polycondensation the low molar mass of lactic acid Prepolymer on the extruder. When the reaction temperature is 150 ℃, the catalyst dosage is 0.5% and the screw speed is r/min, the molar mass of polylactic acid can be improved quickly and effectively by the double screw reaction extrusion polycondensation, and the dispersion coefficient of the reaction extrusion product is reduced and the uniformity becomes better.
Through the comparison of DSC curves, it is found that the crystallinity of polylactic acid obtained by reactive extrusion polycondensation is decreased, which is beneficial to improve the brittleness of polylactic acid material in the process of use.
1) Sampling The corn and other shell crops are crushed, the starch is extracted, then the starch is made into the refined glucose.
Much of the technology has been overcome by subtracting the crushing process and directly extracting raw materials from a large number of crops.
Glucose is fermented in a manner similar to beer or alcohol, and glucose is fermented to form lactic acid, which is similar to food added to the human muscle tissue.
3) Intermediate Type Products
The lactic acid monomer is transformed into intermediate product-----------------------lactide.
After the monomer is purified by vacuum, the action of the Open loop is completed by a dissolution process without solvent, so that the monomer is polymerized.
5) Polymer Modification Because the molecular weight of the polymer and the crystallinity of different, can make the material characteristics of the change of space is very large, so because of different applications of products, the PLA do different modifications.