PLA Polylactide

Polylactic acid or polylactide (PLA) is a biodegradable polyester from fermented corn starch, cane sugar, wheat starch. It can be processed like most thermoplastics into fiber and film. PLA is often made into biodegradable plastic cups, but cannot hold hot liquids unless it is modified into PDLA or PLLA, which increases its melting and glass transition temperatures significantly.

In packaging PLA is used as biodegradable loose-fill, compost bags, sandwich packaging, and disposable cutlery. It is also used for biodegradable sutures, nappies, feminine hygiene products and disposable garments. PLA is more expensive than petroleum-based plastics, but its price has been falling as production increases.

NatureWorks is the world's biggest commercial manufacturer of PLA bioplastic. Its range of PLA consumer products can be found here. Technical data sheets, fact sheets and processing guides are available here.

Some of the Australian brands which use PLA for its bottles are

• Natures Organics haircare line
• Cool Change natural spring water

PLA is compostable and biodegradable in industrial composting conditions, but it will not degrade or disintegrate on the supermarket shelves. In order to degrade, PLA must be exposed to temperatures greater than 60°C and relative humidity greater than 90% (these heat and moisture conditions are optimal for naturally occurring microorganisms to act on the PLA) for approximately 60 to 80 days; after which it composts into carbon dioxide, water, inorganic compounds and biomass. Natureworks advises that PLA will NOT decompose in backyard or home composters (due to lack of temperature and inconsistent conditions). PLA will also not degrade in landfills, due to low oxygen and temperature drops. Industrial composters with carefully regulated temperature, moisture and turning are required.

There are some laboratory tests though which show that PLA can decompose into carbon dioxide and water, such as the one by University of Nebraska. Another study by Iowa State University and University of Costa Rica showed results of visible degradation, but did not claim complete decomposition. Suming Li & Michael Vert's chapter on biodegradation of aliphatic polyesters in the book Degradable Polymers: Principles and Applications claimed that "in particular, it is now well known that PLA polymers degrade completely and rather rapidly in a compost where the temperature is usually between 50 and 60C."

There's another discussion on this on the Greener Package knowledge exchange on sustianable packaging.