35.3 Degradable Polymers

2026 Syllabus Objectives

By the end of these notes, you should be able to:

  1. Recognise that poly(alkene)s are chemically inert and can therefore be difficult to biodegrade.
  2. Recognise that some polymers can be degraded by the action of light.
  3. Recognise that polyesters and polyamides are biodegradable by acidic and alkaline hydrolysis.

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What is Biodegradation?

Biodegradation means being broken down naturally by living things — mainly bacteria and fungi — in the environment. When a material biodegrades, microorganisms (tiny living things too small to see) feed on it and break it apart into simpler, harmless substances.

Not all polymers (long-chain molecules made of repeating units) biodegrade easily. This is a major environmental problem, because plastic waste can last for hundreds of years in the ground or ocean.

Objective 1 — Poly(alkene)s Are Chemically Inert and Hard to Biodegrade

Poly(alkene)s are a group of addition polymers made from alkene monomers. Common examples include:

  • Poly(ethene) — used in plastic bags and bottles
  • Poly(propene) — used in food containers and ropes
  • Poly(chloroethene) (PVC) — used in pipes and window frames

Why Are Poly(alkene)s So Stable?

The backbone (main chain) of a poly(alkene) is made entirely of carbon–carbon single bonds (C–C). These bonds are:

  • Very strong — they require a lot of energy to break
  • Non-polar — the electrons are shared equally, so there is no part of the chain that is slightly positive or slightly negative

Because the chain has no weak spots and no electrically uneven areas, it is very hard for chemicals or microorganisms to attack it. Chemists describe this as being chemically inert, which simply means the polymer does not react easily with other chemicals.

Why Is This a Problem?

Because poly(alkene)s are chemically inert:

  • Bacteria and fungi cannot break them down — the enzymes (natural biological tools) that microorganisms use cannot grip onto and break the C–C bonds
  • These plastics persist (stay around) in landfill sites and oceans for hundreds of years
  • They cause serious harm to wildlife and pollute the environment

In short: The very property that makes poly(alkene)s useful (strength and stability) is exactly what makes them an environmental problem.

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