Polylactic Acid (PLA) is thermoplastic plastic using 100% plant-origin raw materials, and lends itself easily to injection molding, extrusion molding, and blow molding. In addition, it is a plastic resin that can be synthesized without using any petroleum based or chemical based raw materials. Furthermore, it has the excellent environmental characteristic that when this plastic is disposed of in soil, it is completely decomposed into water (H₂O) and carbon dioxide (CO₂) by the enzymes produced by the bacteria in the soil.

Although the presence of this plastic was confirmed more than ten years ago, the method of manufacturing it industrially on a large scale had not been established, and it was almost never specified for use in mass produced items. However, Cargill Dow LLC, which is a joint venture between Cargill Inc. and Dow Chemicals Inc. of USA, succeeded in developing an industrial method of mass manufacturing lactic acid, and it started to be sold in the market. At present, this company has changed its name to NatureWorks LLC and is expanding its business.

The raw material for the polylactic acid plastic is of vegetable origin as mentioned above. At present, starch or sugar (glucose) is being used. In other words, the raw materials will be corn or various tubers, sugarcane, sugar beets, etc. When using starch as the raw material, a reaction called hydrolysis occurs when water is added to starch, it chemically changes to glucose. This is the same reaction as that which occurs when we chew rice and it gradually tastes sweet.

Next, lactic acid bacteria (lactobacillus) are added to the glucose. These microorganisms called lactic acid bacteria have the ability to chemically convert glucose into lactic acid. Lactic acid is a material that is synthesized naturally inside the human body, and it has been known to cause muscle pain such as neck pain or shoulder pain when it accumulates in the muscles.

Next, by carrying out a treatment called dehydration reaction of this lactic acid, it is possible to change it into a material called lactide. There are two types of lactide, namely, L-lactide and D-lactide, but mostly it will be L-lactide. Although whether the result of reaction is L-lactide or D-lactide depends on the type of lactic acid bacteria, not many bacteria have been found that can be used for manufacturing D-lactide.

Next, by carrying out processing called ring opening polymerization of the above lactide, it is possible to obtain polylactic acid plastic.

Polylactic acid is a polymer and is thermoplastic. Therefore, it melts when heated to a high temperature and becomes a solid when cooled. The glass transition temperature is around 57°C. In other words, it is possible to mass produce items by injection molding using molds.

Injection molding of normal polylactic acid plastic can be made by setting the mold temperature to about 30°C to 40°C. Even the design of molds can be made once some experience has been gained. However, since the withstanding temperature of the molded items will be around 60°C, and since even their mechanical strength is also not high, the applications of the molded items will be limited to those satisfying these conditions. Transparent grades are also available. As a result of research in various companies, polylactic acid plastics are now being sold that can withstand temperatures of around 120°C. In the case of these grades, care should be taken during the mold design because the fluidity is bad, mold releasing is extremely bad, and also the cooling time becomes long. The scope of applications of polylactic acid plastics has become considerably wide due to the advent of the high heat resistant grade. Studies are now under way in various fields about the application of these plastics.