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3.12.2Organic Chemistry

Biodegradability and Disposal of Polymers — Oxford AQA International A Level Chemistry Revision Notes & Topical Questions

5 min read 4 parts Lesson 45 of 55

📚 Oxford AQA International A Level Chemistry Hub / Topical Revision
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Part 1 of 4Why Polymers Persist

3.12.2 Biodegradability and Disposal of Polymers
Why Polymers Persist
Addition polymers
  • Poly(alkenes) have a carbon backbone of non-polar C–C and C–H bonds that is chemically inert and not attacked by water or enzymes.
Not biodegradable
  • Micro-organisms cannot break the saturated carbon chain, so these polymers remain in landfill for many years.
Condensation polymers
  • Polyesters and polyamides have polar C=O bonds in the chain that attract nucleophiles such as water.
Hydrolysis
  • Acid, alkali or enzymes can hydrolyse the ester or amide links, so some are biodegradable or photodegradable.

Part 2 of 4Disposal Methods

Landfill
  • Cheap and simple, but it uses land and many polymers stay for decades without breaking down.
Incineration
  • Burning waste polymers produces heat that can generate electricity, but it releases CO₂, which adds to global warming.
Toxic gases
  • Burning some polymers makes harmful gases, such as HCl from PVC, so scrubbers must remove them from the exhaust.
Recycling
  • Sorted plastics can be melted and remoulded, which saves crude oil and energy, but mixed plastics are hard to sort.
Feedstock recycling
  • Polymers are broken back into monomers or small molecules and used to make new polymers, which suits polyesters such as PET.

Part 3 of 4Sustainable Alternatives

1
Biodegradable polymers such as poly(lactic acid) are made from renewable plant materials and break down by hydrolysis of ester links.
2
Using renewable feedstocks reduces the demand for crude oil, a finite fossil resource.
3
Photodegradable plastics contain groups that absorb sunlight and break the chain, but they may leave small fragments in the soil.
4
Choosing a disposal method needs a balance between energy cost, atmospheric pollution, land use and the value of the recovered material.

Part 4 of 4Exam Checklist & Tips

3.12.2 – Key Points for the Exam

  • Biodegradable Able to be broken down by micro-organisms into simpler substances.
  • Incineration Disposal by burning, often with energy recovery.
  • Feedstock recycling Breaking polymers into chemicals to use in making new materials.
  • Hydrolysis Breaking of a bond by reaction with water.

Common Mistakes

  • Saying all polymers are biodegradable; addition polymers made from alkenes generally are not.
  • Forgetting that burning plastic gives CO₂ and sometimes toxic gases like HCl.
  • Saying recycling uses no energy; sorting, melting and processing all need energy.
  • Explaining non-biodegradability by size alone instead of by the unreactive non-polar C–C chain.

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