3.4.9 Polymers - Biodegradability and disposal of polymers

Specification

Students should:
  • understand that polyalkenes are chemically inert and therefore non-biodegradable
  • understand that polyesters and polyamides can be broken down by hydrolysis and are, therefore, biodegradable (mechanisms not required)
  • appreciate the advantages and disadvantages of different methods of disposal of polymers
  • appreciate the advantages and disadvantages of recycling polymers

Properties of addition polymers

Addition polymers are polyalkenes. The molecules are saturated, as all of the bonds holding the carbon chain together are single. This makes them generally unreactive and chemically inert. This has both advantages and disadvantages. The advantage is that they are safe and durable, but this durability means that they do not biodegrade when left in the environment, making them a pollution hazard.

They are also difficult to dispose of and need to be burned under special conditions to avoid the formation of extremely toxic combustion by-products such as dioxins.


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Properties of condensation polymers

Condensation polymers all contain either the amide or ester linkages. These linkages make the polymers reactive towards both acids and bases, which cause the polymer structure to break down. This is called hydrolysis.

Hydrolysis

This means that condensation polymers are biodegradable and do not pose the same pollution hazard as addition polymers.


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Disposal of polymers

Non-biodegradable polymers are disposed of in three main ways:

Landfill is exactly what it sounds like. he polymers are buried in sites dedicated to waste. However, the amound of land available is limited and suitable sites often fill up rapidly.

Incineration of polymers releases a lot of heat energy, which can be used to generate electricity. However, there are problems with incineration. Carbon dioxide is produced, which adds to global warming. Toxic gases are also produced, unless the polymers are incinerated at high temperatures.

Recycling polymers is a good idea, but not always practical. Many polymers are mixed with other materials and paints or dyes and separation is difficult and expensive. Many polymers now carry labels to indicate how they should be recycled. The clear advantage of recycling is protection of useful hydrocarbon resources for the future.


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