ABSTRACT
Poly(lactic acid) (PLA) is a plant-based, biodegradable plastic made from the fermented sugars of crops such as corn, beet, and sugarcane. The l-and d-isomers of lactic acid are used, either in combination or separately, to synthesize high-molecular weight PLA plastic, which is approved by the Food and Drug Administration for use in food packaging and biomedical applications. PLA has a glass transition temperature and melt temperature of about 55°C and 175°C, respectively. It is colorless, glossy, and rigid and has properties that are similar to polystyrene. It is an aliphatic polyester, which means that it lacks the highly stable, six-carbon rings typically associated with hard and extremely durable polyesters (such as polyethylene terephthalate), which are generally nonbiodegradable. In the presence of moisture and heat, PLA breaks down into smaller hydrocarbon compounds that can be absorbed and metabolized by microorganisms in a process called chemical hydrolysis. This process can take about six months to two years (Garlotta 2001).This is the primary reason that PLA is considered as an attractive substitute for petroleum-based plastics that are used in many single-use disposable packagings, which end up in landlls and pollute waterways for centuries. In the last several years, vast amounts of biodegradable solid PLA has been extruded for thermoforming and molding into food and beverage packaging applications. Solid PLA, however, requires more material and is heavier than plastic foams. As the food and lm packaging industries are looking for material that reduces the amount of polymer used, microcellular foams are considered a viable alternative to solid plastics.
