Biodegradable Bio-based Transparent Polylactic Acid Particle

Synthesis of Polylactic Acid method and process
1.Polylactic Acid production is based on lactic acid as raw material, the traditional lactic acid fermentation mostly with starchy raw materials, at present, the United States, France, Japan and other countries have developed the use of agricultural by-products as raw materials for the fermentation production of lactic acid, and then the production of polylactic acid.
Direct polycondensation method
Condensation method is the lactic acid monomer for direct condensation, also known as one-step polymerization method. In the presence of dehydrating agent, the hydroxyl and carboxyl groups in the lactic acid molecule are dehydrated by heat, and oligomers are synthesized by direct condensation. Add catalyst, continue to raise the temperature, low relative molecular mass of polylactic acid polymerization into higher relative molecular weight of polylactic acid.
Two-step process
Make lactic acid to generate a ring dimer propylene glycol ester, and then ring-opening polycondensation into polylactic acid. This technology is more mature, the main process is the raw material by microbial fermentation to produce lactic acid, and then after refining, dehydration oligomerization, high temperature cracking, and finally polymerization into polylactic acid.
Preparation of high molecular weight PLA by reaction extrusion
The combination of intermittent stirring reactor and twin-screw extruder is used to carry out continuous melt polymerization experiments to obtain PLA with molecular weight up to 150,000 made from lactic acid by continuous melt polycondensation. Higher molar mass PLA was prepared by further polycondensation of low molar mass lactic acid prepolymer on the extruder using a twin-screw extruder. The molar mass of PLA could be increased quickly and effectively by twin-screw reaction-extrusion polycondensation at a reaction temperature of 150 °C, a catalyst dosage of 0.5%, and a screw speed of 75 r/min, and the dispersion coefficient of the reaction-extruded product decreased and the homogeneity became better. Comparison of the DSC curves showed that the crystallinity of PLA obtained by reaction extrusion polycondensation was reduced, which was beneficial to improve the brittleness of PLA materials in the process of use.
2.Process
(1) Material extraction
Shell crops such as corn are crushed and starch is extracted from them, and then the starch is made into unrefined glucose. Many high technologies have overcome the process of subtracting the milling and extracting raw materials directly from a large number of crops.
(2) Fermentation
Glucose is fermented in a manner similar to the production of beer or alcohol, and glucose is fermented into lactic acid similar to that added to food for use in human muscle tissue.
(3) Intermediate products
Lactic acid monomer is converted into an intermediate product, lactic acid with reduced water, or propyl lactate, by a special concentration process.
(4) Polymerization
After the monomer of propylene glycol ester is purified by vacuum, a solvent-free dissolution process is used to complete the ring-opening action, so that the monomer is polymerized.
(5) Polymer Modification
Due to the different molecular weight and crystallinity of Polymers, there is a lot of room for change in material properties, so PLA is modified in different ways for different applications.

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(1)Polymers：The advantage of Polymers is that they can be easily formed into the desired shape using a variety of techniques such as solution casting, melt moulding, or machining. As a result, polymer-based implants are relatively inexpensive to manufacture. Polymers can also react so that different chemical molecules can attach to the surface of the implant, making it more compatible with the body's surroundings.

(2)Catalysts And Auxiliaries：A catalyst is a substance that changes the rate of reaction in a chemical reaction while its own composition and quality remain unchanged after the reaction. A catalyst that speeds up a reaction is called a positive catalyst (Positive Cata-lyst), and one that slows it down is called a negative catalyst (Negative Catalyst) or retardant. Generally speaking, catalysts are positive catalysts.

Auxiliary agent refers to the industrial and agricultural production, especially in chemical production, in order to improve the production process, improve product quality and yield, or to give the product some unique application performance, usually need to add some auxiliary chemicals. It is a large class of important auxiliary raw materials in chemical production, can give the product with special properties, improve the use of finished products; can accelerate the speed of chemical reaction, improve product yield; can save raw materials, improve processing efficiency, widely used in the chemical industry.