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The properties of plastics are determined by the polymers that constitute the unit. Based on this, plastics can be modified into biodegradable products by varying the constituents synthetically. Their chemical structures vary due to the substituting polyesters in the polymer chain. Let’s study about the chemical differences and structure of green plastics; PHA and PLA. Amylose and Amylopectin are the major polymer components of starch. In the link structure, all identical chain points are connected to –CH2OH group.
The oxygen in the ring structure chain facilitates degradation when reacted with water. Any hybrid variety can be produced with two components: renewable natural polymer (starch) and petroleum based synthetic polymer (PCL). • Polylactide (PLA) is a bioplastic basically made from starch, the basic building material. Here lactic acid (CH3CHOHCOOH) is produced through fermentation where microorganisms convert sugar feedstock into lactic acid.
The lactic acid thus isolated is depolymerized to lactide and by Ring-opening polymerization with catalysts it is converted into Polylactide polymer of high molecular weight. Based on the particle size, the rate of biodegradability and transparency varies. They find use in soluble fibers, compose bags and renewable products. • Polyhydroxyalkanoates (PHA) polymers are produced naturally by microorganisms directly from sugar feedstock. The polymer is isolated, purified and processed. These components can be controlled by varying the ratio of sugar feedstock.
Synthesized PHA is copolyester composed of 3-hydroxy fatty acids hydroxybuterate, hydroxyvalerate and hydroxyhexanoate. In all PHAs the hydroxyl substituted carbon atom is steriochemical -R configuration. Since they are composed of short chain and long chain length –R groups, they are used for a variety of commercial applications. References Journal of Applied Microbiology, 2007, Pp 1437-1449 Stevens, E. S. , Green Plastics: An introduction to the New Science of Biodegradable Plastics, Princeton University Press, 2003