ANALYSE PROGRESS IN THE DEVELOPMENT AND USE OF A NAMED BIOPOLYMER. THIS ANALYSIS SHOULD NAME THE SPECIFIC ENZYME USED OR ORGANISM USED TO SYNTHESISE THE MATERIAL. How is PLA developed into different plastics? Refer to processes used and conditions (equations, catalyst/enzyme, temp, pressure) how are the different plastics used? Structural Formula of PLA
Structural Formula of PLA
Biopolymers such as Polylactic Acid (PLA) are still in early stages of development. PLA is part of the ‘biopolyester’ group. It shows a large range of properties and therefore is one of the most promising biopolymers at the present and heading into the future. It is derived from renewable resources such as corn (biomass), which ultimately allows PLA to biodegrade under certain
conditions such as the presence of oxygen. PLA is produced from biomass products such as corn. The corn is harvested and then milled to extract starch from the raw materials. From the starch, dextrose (glucose) is produced. The dextrose is then fermented, transforming into lactic acid.
lactic acid + carbon dioxide
CH3CHOHCOOH + CO2
The lactic acid is then altered into a polymer by condensation polymerisation, forming long chain molecular compounds into PLA. Lactic acid has been produced on the industrial scale since the 19th century and is mainly used in the food industry, cosmetics, pharmaceuticals and animal feed. The synthesis of PLA is a multistep process which starts from the production of lactic acid and ends with polymerisation, with an intermediate step for the formation of the lactide. There are two main monomers used; lactic acid and lactide. Synthesis of PLA can follow three main routes: 1) Lactic acid monomers are directly condensation polymerised to yield a brittle polymer, unless external coupling agents are attached to increase chain length. This needs to occur at less than 200℃ as the enzyme catalyst will denature. In this process, water is a co-product which is expelled, causing chain length to transfer to a low molecular weight. 2) Azeotropic dehydrative condensation of lactic acid can yield high molecular weight PLA without the use of chain extenders. 3) The most common route to PLA is Ring Opening Polymerisation of lactide with various metal catalysts (typically tin octoate) in solution, in the melt, or as a suspension. The metal-catalysed reactions often triggers the conversion of an active substance into an inactive substance (racemization) of the PLA, reducing its chain rule (stereoregularity) compared to the starting material. Regular condensation polymerisation leaves PLA brittle, and so ROP is an interesting alternative to the use of plasticisers that are a possible health risk. Development into PLA has discovered that the biopolymer does not emit toxic fumes when incinerated, and so this presents a method for disposing plastics made from PLA. This does not pose health hazards and risks to societal use of the produced plastics. PLA can be recycled to monomer units by thermal depolymerisation (or hydrolysis) at 190-245℃. When purified, the monomer (either lactic acid or lactide) can be used for the re-manufacture of PLA with no loss of original properties. The SPI resin ID code of 7 indicates how and with what other plastics with similar densities it can be recycled. PLA is quickly becoming a popular alternative to traditional petroleum based plastics. It is poised to play a big role as a viable, biodegradable replacement to plastic grocery bags. Until recently, it was not feasible to use polylactides for packaging because of their high price (US $500/kg). PLA consumption in 2006 was only 60,000tonnes/year, and at present, only 30% of lactic acid is used for PLA production. Therefore PLA presents a high potential for development. As long as the basic monomers (lactic acid) are produced from renewable resources by fermentation, PLA complies...
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