Polylactic acid (PLA) is a biodegradable plastic primarily made from renewable biomass resources. Due to its excellent degradability, biocompatibility, and processing adaptability, it has received widespread attention globally in the context of promoting green and low-carbon development. As a typical bio-based polymer, PLA can not only decompose into carbon dioxide and water under specific environmental conditions, but also re-enter the carbon cycle through plant photosynthesis, thus being considered one of the important alternatives to traditional petroleum-based plastics.
PLA is synthesized using lactic acid as the monomer. Lactic acid is mainly obtained through fermentation of crops rich in starch or sugars, such as corn, sugarcane, and cassava. The fermented lactic acid is dehydrated to form lactide, which is then subjected to ring-opening polymerization to produce long-chain polylactic acid. Depending on the polymerization process and stereochemistry, PLA materials with different crystallinity and properties can be obtained. High L-isomers impart higher crystallinity and heat resistance, while copolymerization modification can adjust its flexibility and degradation rate to meet diverse application needs.
From a performance perspective, PLA possesses advantages such as good transparency, a wide processing window, and moderate tensile strength and modulus. It can be manufactured into films, sheets, fibers, packaging containers, and disposable tableware through various conventional plastic processing techniques, including injection molding, extrusion, blow molding, and thermoforming. However, its glass transition temperature is approximately 55–65℃, and its melting point is approximately 150–170℃, resulting in relatively limited heat resistance. Furthermore, it is prone to accelerated hydrolysis in humid or high-temperature environments, which to some extent limits its direct use in high-temperature load-bearing or long-term outdoor applications.
PLA's outstanding advantage lies in its biodegradability. Under industrial composting conditions (temperature 58±2℃, humidity above 50%, aerobic environment), it can be gradually decomposed into lactic acid by enzymes secreted by microorganisms, and then converted into carbon dioxide and water, with the entire cycle typically lasting several months to a year. However, in non-composting environments such as the ocean or ambient-temperature soil, the degradation rate slows significantly; therefore, its environmental benefits need to be assessed in conjunction with specific application scenarios.
In industrial applications, PLA is widely used in food packaging, disposable tableware, express delivery cushioning materials, medical surgical sutures, and drug delivery carriers, with significant advantages, particularly in scenarios emphasizing low carbon footprint and compostability. Furthermore, its mechanical properties and degradation controllability can be further optimized by blending with biodegradable polymers such as polycaprolactone (PCL) and polyhydroxyalkanoates (PHA), or by combining it with natural fibers.
Overall, PLA represents an important direction in the development of bio-based and biodegradable plastics. Its renewable raw materials and ability to return to nature after use align with global strategic needs for plastic reduction and carbon neutrality. In the future, with breakthroughs in raw material diversification, performance improvements, and controllable degradation technologies, PLA is expected to achieve functional replacement of traditional plastics in more fields and provide solid support for building a sustainable materials system.