Views:179 Author:Site Editor Publish Time: 2019-06-23 Origin:Site
Polylactic acid is a polymer obtained by polymerizing lactic acid as a main raw material which is sufficient and can be regenerated. The production process of polylactic acid is non-polluting, and the product can be biodegraded to achieve circulation in nature, so it is an ideal green polymer material. In addition to biodegradability, products made of polylactic acid have characteristics of biocompatibility, gloss, transparency, hand and heat resistance. Currently, PLA is mainly used in clothing, industry construction, agriculture, forestry, medical and other fields. There are mainly three methods of PLA manufacturing.
Under the action of a catalyst, lactic acid molecules directly synthesize polylactic acid by polycondensation reaction. The method has low cost, high yield, and can obtain a relatively pure product without separating substances, but the obtained product is not relatively high in molecular weight.
An organic solvent is added to the reaction system which is capable of dissolving the polymer but does not participate in the reaction, and can form an azeotrope with the water in the reaction system. Then the azeotropic reflux can continuously remove water from the reaction system, which ensures that the reaction proceeds in the positive direction to synthesize polylactic acid. Solution polymerization requires a large amount of solvent and is susceptible to environmental pollution.
First, the lactic acid is melt-polycondensed to obtain a low-molecular prepolymer which is further polymerized at a temperature higher than its glass transition temperature and lower than its melting point, then obtains a polymer having a relatively high molecular weight Lactic acid. The polylactic acid prepared by this method has a relatively high molecular weight, but ittakes a long time.
The biomedical industry is the earliest application area of polylactic acid. Polylactic acid is highly safe for human body and can be absorbed by tissues. In addition to its excellent physical and mechanical properties, it can also be used in biomedical fields, such as disposable infusion tools, disposable surgical sutures, drug-relieving packaging agents, and artificial fractures, tissue repair materials, artificial skin, etc. Polylactic acidigh with high molecular weight has very high mechanical properties and has been used as a substitute for stainless steel in Europe and the United States. It is widely used as a new type of orthopedic internal fixation material such as bone nails and bone plates, which can be absorbed and metabolized by the human body. The patient was relieved of the second surgery.
Extrusion grade resin is the mainapplication of PLA which is mainly used for packaging fresh fruits and vegetables in large supermarkets. This type of packaging has become an important member of the European market chain. Secondly, it is used to promote safe, energy-saving and environmentally friendly packaging of electronic products. In these applications, PLA's high transparency, high gloss, high rigidity and other advantages are reflected, which is now the leading direction of PLA applications. In addition, the application of extrusion grade resin in horticulture has begun to gain attention, and it has been applied in the fields of slope greening and sandstorm control.
Polylactic acid is harmless to the human body, which makes polylactic acid unique in the field of disposable articles such as disposable tableware and food packaging materials. Its ability to fully biodegrade is also in line with the high environmental requirements of countries around the world, especially the European Union, the United States and Japan.