Polylactic acid (PLA)

Polylactic acid (also called polylactide, PLA) is a second major biodegradable-plastic alternative, distinguished from PHB/PHAs by being an aliphatic polyester rather than a purely bacterial fermentation product, and by being derived from plant-based, renewable agricultural feedstocks - corn starch, cassava root, or sugarcane - rather than being synthesised directly by microorganisms. Chemically, PLA production starts from two related monomer building blocks: lactic acid itself, and a cyclic diester of lactic acid called lactide. The dominant industrial production route is ring-opening polymerisation of lactide, carried out in solution using a metal catalyst, typically tin octoate, which links many individual lactide monomers together into the long polymer chain that gives PLA its plastic-like physical properties; this particular metal-catalysed reaction produces roughly equal amounts of the two mirror-image (stereoisomeric) forms of lactic acid in the resulting polymer. Like PHB, P …