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Scientists develop new polymers and modify existing polymers.
Polylactic acid (PLA) is a bioplastic that is biodegradable. It can be used to make sandwich containers, plastic cups and plastic cutlery. PLA is made from cornstarch. In the USA large amounts of maize are grown and used to make cornstarch, which has many uses. To make PLA the cornstarch is fermented with microbes to make lactic acid, which is then polymerised.
The structure of PLA is -(-O-CH(CH3)CO-)-
a i Give one way in which the structure of PLA is different from the structure of poly(ethene).
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ii Give one way in which the structure of PLA is similar to the structure of poly(ethene).
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iii Suggest what is meant by bioplastic.
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iv Suggest two reasons why PLA was developed.
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b Copper was considered to be the most suitable material to use for hot water pipes. PEX is now used as an alternative material for hot water pipes. PEX is made from poly(ethene). Copper is extracted from its ore by a series of processes.
1 The low-grade ore is powdered and concentrated.
2 Smelting is carried out in an oxygen flash furnace. This furnace is heated to 1100°C using a hydrocarbon fuel. The copper ore is blown into the furnace with air, producing impure, molten copper.
3 Oxygen is blown into the impure, molten copper to remove any sulfur. The copper is cast into rectangular slabs.
4 The final purification of copper is done by electrolysis.
Suggest the possible environmental advantages of using PEX instead of copper for hot water pipes.
(6)
