Polylactic acid (PLA) is produced without pollution, and the product is biodegradable, enabling it to cycle in nature, making it an ideal green polymer material.
Polylactic acid (PLA) exhibits good thermal stability, with a processing temperature range of 170–230℃. It also possesses good solvent resistance and can be processed in various ways, such as extrusion, spinning, biaxial stretching, and injection blow molding. PLA products are not only biodegradable but also possess good biocompatibility, gloss, transparency, hand feel, and heat resistance. Furthermore, they exhibit certain antibacterial properties, flame retardancy, and UV resistance, making them widely applicable as packaging materials, fibers, and nonwovens. Currently, they are primarily used in clothing (underwear, outerwear), industry (construction, agriculture, forestry, papermaking), and medical and health fields.
Before large-scale industrialization, PLA was priced at $1,000 per kilogram. Later, through industrialization research by Professor Ramani Narayan's research group at Michigan State University, large-scale production was achieved. This technology is now industrialized by Natureworks.
The largest manufacturer of PLA is NatureWorks in the United States, followed by Hisun Biotechnology in China, with current production capacities of 100,000 tons and 15,000 tons respectively. PLA has many applications, including extrusion, injection molding, film stretching, and spinning.
Preparation process
We will mainly discuss the more commonly used ring-opening polymerization method, and its process is roughly as follows:
1) Draw materials
Crushing corn and other husk crops to extract starch, which is then processed into unrefined glucose, has been replaced by advanced technologies that eliminate the crushing process, allowing for direct extraction of raw materials from large quantities of crops.
2) Fermentation
Glucose is fermented in a manner similar to that used in beer or alcohol production, and the fermented glucose is transformed into lactic acid, which is added to food and used in human muscle tissue.
3) Intermediate products
Lactic acid monomers are converted into an intermediate product—reduced water lactic acid, or lactide—through a special concentration process.
4) Aggregation
After being purified under vacuum, lactide monomers undergo ring-opening via a solvent-free dissolution process, which polymerizes the monomers.
5) Polymer modification
Because of the differences in molecular weight and crystallinity of polymers, there is a great deal of room for variation in material properties. Therefore, PLA is modified in different ways depending on the application.
