Polylactic acid
Encyclopedia : P : PO : POL : Polylactic acid
Polylactic acid or Polylactide (PLA) is a biodegradable, thermoplastic, aliphatic polyester derived from lactic acid. It can be easily produced in a high molecular weight form through ring-opening polymerization using a stannous octoate catalyst, but for laboratory demonstrations tin(II) chloride is often employed.
Due to the chiral nature of lactic acid several distinct forms of polylactide exist: poly-L-lactide (PLLA) is the product resulting from polymerization of lactid acid in the L form. PLLA has a crystallinity around 37%, a glass transition temperature between 50-80° C and a melting temperature between 173-178° C. The polymerization of a mixture of both L and D forms of lactic acid leads to the synthesis of poly-DL-lactide (PDLLA) which is not crystalline but amorphous. Polylactic acid can be processed like most thermoplastics into fiber (for example using conventional melt-spinning processes) and film. PLA is currently used in a number of biomedical applications, such as sutures, dialysis media and drug delivery devices, but it is also evaluated as a material for tissue engineering. Being biodegradable it can also be employed in the preparation of bioplastic, useful for producing loose-fill packaging, compost bags, food packaging and disposable tableware. In form of fibers and non-woven textiles PLA also has many potential uses, for example as upholstery, disposable garments, awnings, feminine hygiene products and nappies.
PLA is particularly attractive as a sustainable alternative to petrochemical-derived products, since the lactate from which it is ultimately produced can be derived from the fermentation of agricultural by-products such as corn starch or other starch-rich substances like maize, sugar or wheat. PLA is more expensive than many petroleum-derived commodity plastics, but its price has been falling as more production comes online. The degree to which the price will fall, and the degree to which PLA will be able to compete with non-sustainable petroleum-derived polymers, is uncertain.
In December 2005, NatureWorks LLC (Natureworksllc.com), a wholly-owned subsidiary of Cargill Corporation, was the primary producer of PLA in the United States.
Other biodegradable polymers:
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