What is PLA stands for? PLA (polylactic acid) is the most mature, the most widely used and the lowest price bio-based plastics, which will become the ecological environmental protection materials with broad application prospects in the future. PLA is very environmentally friendly and has no pungent smell during processing. PLA is suitable for blow molding, thermoplastic and other processing methods. Here we highlight everything you need to know about PLA, the types, applications, advantages and processes of polylactic acid.
PLA is the fermentation product of microorganisms L_ Lactate is a kind of polymer polymerized by monomer, which has the characteristics of biodegradability, biocompatibility and no environmental protection problems after degradation. It will become a promising ecological environmental protection material in the future. PLA is water-resistant but not high-temperature resistant. Although not water-soluble, microorganisms in the marine environment can also degrade them into carbon dioxide and water. This plastic is similar to transparent polystyrene, showing a good appearance (shiny and transparent), but it is hard. For brittle materials, modification is needed in most practical applications (for example, plasticizers are used to improve their flexibility). During the PLA injection molding, the base is not warped, so it can print more difficult models, so it is more suitable for printing large models.
There are several different types of Polylactic Acid to include Racemic PLLA (Poly-L-lactic Acid), Regular PLLA (Poly-L-lactic Acid), PDLA (Poly-D-lactic Acid), and PDLLA (Poly-DL-lactic Acid).
The thermal stability of PLA is good, the processing temperature is 170-230 ℃, and it has good solvent resistance. It can be processed in many ways, such as extrusion, spinning, biaxial stretching and injection blow molding. In addition to biodegradation, products made of PLA have good biocompatibility, glossiness, transparency, the hand feel and heat resistance, and have certain bacteria resistance, flame retardant and UV resistance. Therefore, they are widely used as packaging materials, fibers and non-woven fabrics. The products are mainly used in clothing (underwear, coat), industry (construction, agriculture, forestry, etc.) Paper) and medical and health.
Generally speaking, the process of polylactic acid (PLA) is based on lactic acid. At present, there are many kinds of synthesis methods, the more mature is the direct polycondensation of lactic acid, the other is the synthesis of lactide from lactic acid, and then ring-opening polymerization under the action of the catalyst. There is also a solid state polymerization method.
Direct PolymerizationOf Lactate
Since the 1930s-1940s, research has been started. However, the key technologies such as water removal in the reaction can not be solved well, so the molecular weight of the products is low (all below 4000), the strength is very low, and it is easy to decompose, and it is not practical.
In order to make the reactants further polycondensate at 220-260 ℃ and 133pa, the relative molecular weight of PLA above 4000 is obtained by heating up the lactic acid in inert gas and reducing pressure slowly. However, the reaction time of the method is long, the product will aging and decompose, discolor and uneven at later high temperature. The solution polymerization method was used by Mitsui chemical company to directly polymerize the lactic acid to produce PLA.
The main characteristic of direct method is that the synthetic PLA does not contain catalyst. Therefore, when the polycondensation is carried out to a certain extent, the system will have equilibrium state, which needs to be broken by heating and pressure, and the reaction conditions are relatively harsh. In recent years, through the innovation and improvement of technology, direct polymerization has made some progress. It should be applied in the industrial production in the near future with the continuous maturity of technology.
Open Loop Polymerization
Open loop polymerization is a more widely used production method in the world. As early as the middle of the 20th century, researchers of a company used open-loop polymerization to obtain high molecular weight PLA. In recent years, the research on the synthesis of PLA mainly focused on the ring opening polymerization of lactide.
Boehringer Ingelheim company in Germany produced the PLA series products in the market under the commercial name; The polylactic acid produced by Cargill company in the USA has been processed by melt spraying and spun-bond, and the medical meta textile products have been developed. The open-loop polymerization is mainly based on stannous octanoate as initiator, with a molecular weight of millions, high mechanical strength and two steps of polymerization and separation.
– The first step is to prepare lactide by dehydration and cyclization;
-The second step is to prepare the poly (lactide) by ring opening polymerization;
However, the purity of catalyst and monomer of this open loop polymerization method is very high when polymerization. Even the very small impurities will make the molecular weight of PLA lower than 100000. Moreover, polymerization conditions such as temperature, pressure, catalyst type and amount, reaction time will greatly affect the molecular weight of PLA. Therefore, the synthesis of high molecular weight PLA is a technical difficulty.
Solid State Polymerization
This method is to get the low molecular weight resin obtained by direct polymerization under the condition of vacuum and temperature between TG and TM to improve its polymerization degree and molecular weight, thus improving the strength and processing performance of the material. The common open-loop polymerization method has the following processes:
-After the corn and other shell, crops are crushed, the starch is extracted from the materials, and then the starch is made into unsound glucose. Now many high-tech have overcome the process of subtracting crushing, and directly extract raw materials from a large number of crops.
– Glucose is fermented in a similar way to beer or alcohol, and glucose fermentation becomes similar to the lactate added in human muscle tissue.
– The intermediate product transforms the monomer of lactate into the intermediate product, water-reducing lactate, i.e. lactide, by special concentration process.after vacuum purification, the polymerization of the monomer is completed by a solvent free dissolution process.
– Polymer modification: because of the difference of molecular weight and crystallinity of polymer, the change space of material properties is very large. Therefore, PLA is modified differently due to different products.