Biodegradability (A2 Only)
Chemistry: AQA A Level, topic 6.6.2
Disposal and Biodegradability of Polymers
Polymers can be disposed of in different ways depending on their properties. Polyalkenes are non-biodegradable. But polyesters and polyamides are biodegradable.
Disposal: incineration
- Incineration is burning the polymers to produce energy for electricity.
- This reduces landfill space. But toxic gases are released and greenhouse gases are produced.
Disposal: recycling
- Recycling saves raw materials, which is important when considering that many polymers are produced from crude oil.
- But polymers need to be separated and organised - an expensive process.
Disposal: landfill
- Landfill is the most common method of disposal of waste in the UK.
- Many landfills are now reaching full capacity.
- It is worse for polyalkenes because they biodegrade very slowly.
- More biodegradable polymers, such as polyesters and polyamides, are better.
Biodegradability of polyalkenes
- Polyalkenes are made up of strong carbon-carbon and carbon-hydrogen bonds and so biodegrade slowly in landfill sites.
- We say they are non-biodegradable.
Biodegradability of polyesters and polyamides
- Polyesters and polyamides can be broken down by hydrolysis and so are biodegradable.
- This reactivity is due to weak polar bonds in the polymer chain.
- Nucleophiles, such as water, can break down the polyester or polyamide chains.
- The hydrolysis reaction can be achieved in either base (OH-) or acid (H+).
- The acidic hydrolysis produces the original monomers.
- Basic hydrolysis produces the salt of the dicarboxylic acid monomer.
Test yourself on Biodegradability (A2 Only)
What of the following is NOT a negative of incineration?