Disposal of Addition Polymers

Addition polymers — such as poly(ethene) (bags, bottles), PVC (pipes, window frames), PTFE (non-stick coatings) and polystyrene (packaging) — are everywhere in modern life. They are cheap, strong and unreactive, which makes them brilliant materials to use — but a real headache to throw away.

The core idea the examiner wants is one word: non-biodegradable.

What 'non-biodegradable' means. A biodegradable material can be broken down by microorganisms (bacteria and fungi) in the soil. A banana skin rots in weeks because microbes can digest it. Addition polymers cannot be digested by microbes, so they do not rot — they just stay in the environment for hundreds of years.

Why microbes cannot break them down (the chemistry):

• Addition polymers have a long, all-carbon C–C backbone held together by strong covalent bonds.
• This backbone has no functional groups (no reactive –OH, –COOH or amide groups) for microbes' enzymes to attack.
• So the polymer is chemically unreactive — it does not react with water, acid, alkali or the chemicals microbes use.

Because they are so unreactive and long-lasting, addition polymers build up as litter, fill landfill sites and end up in rivers and oceans, where they harm wildlife.

The disposal problem in one line: the very properties that make addition polymers useful (cheap, strong, unreactive) are exactly what make them an environmental problem when we try to get rid of them.

There are three main ways to dispose of waste plastics, and each has advantages AND problems. Exam questions almost always ask you to evaluate them — so learn one good point and one drawback for each.

Route	What happens	Advantage	Main problem(s)
Landfill	Plastic is buried in large pits	Simple and cheap	Takes up space; land is finite; plastic persists for hundreds of years
Incineration	Plastic is burnt	Releases heat → generates electricity; reduces volume	Produces CO₂ (greenhouse gas) and toxic gases (e.g. HCl from PVC)
Recycling	Plastic is sorted, melted and re-moulded	Saves crude oil; reduces waste	Must be sorted into types (difficult/costly); quality can fall

Key idea: none of the routes is perfect. A good answer states the benefit of a route and its drawback, then makes a judgement.

Burning waste plastic — incineration — is attractive because the energy released can be used to heat water, make steam and generate electricity, and it greatly reduces the volume of waste. But there are serious problems with the gases produced.

Problem 1 — carbon dioxide. All plastics contain carbon, so burning them releases carbon dioxide (CO₂), a greenhouse gas that adds to climate change.

Problem 2 — incomplete combustion. If there is not enough oxygen, burning gives carbon monoxide (CO) — a toxic gas that is poisonous because it stops the blood carrying oxygen.

Problem 3 — PVC releases hydrogen chloride. This is the favourite exam point. PVC = poly(chloroethene) contains chlorine atoms. When PVC is burnt, the chlorine is released as hydrogen chloride (HCl) gas:

$\text{PVC (contains Cl)} \xrightarrow{\text{burn in air}} \text{CO}_2 + \text{H}_2\text{O} + \text{HCl}$

• HCl is acidic and toxic — it is corrosive and contributes to acid rain.
• This is why PVC must NOT be burnt in ordinary fires; modern incinerators need special equipment ('scrubbers') to remove the HCl from the waste gases.

Watch the wording: ordinary addition polymers such as poly(ethene) and poly(propene) contain only carbon and hydrogen, so burning them gives only CO₂ and water — not HCl. HCl is specific to PVC (and other chlorine-containing plastics). Do not write that 'all plastics give off HCl'.

Recycling means collecting waste plastic, sorting it by type, then washing, melting and re-moulding it into new products.

Advantages of recycling:

• Saves crude oil — plastics are made from crude oil (a finite resource), so re-using them conserves it.
• Reduces waste sent to landfill and reduces litter.
• Saves energy compared with making new plastic from scratch.

Problems with recycling:

• Plastics must be sorted into separate types — different polymers cannot be melted together, and sorting is difficult, slow and costly.
• The quality of the plastic falls each time it is recycled, so it cannot be recycled endlessly.
• Some plastics are mixed with other materials or contaminated with food, making them hard to recycle.

Better solutions — reduce, reuse, innovate. Because every disposal route has problems, the best answers focus on creating less waste in the first place:

• Reduce — use less plastic; avoid single-use items (bags, straws, bottles). A plastic-bag charge cut bag use sharply.
• Reuse — use items again (refillable bottles, reusable shopping bags) instead of throwing them away.
• Develop biodegradable polymers — new plastics that can be broken down by microbes (e.g. made from plant starch). These rot away naturally and do not persist for hundreds of years.

Exam framing. A typical 4WSD0/1C answer on improving plastic disposal: 'Use biodegradable plastics so they break down naturally', OR 'recycle to save crude oil', OR 'reduce single-use plastic to cut waste at source'. Always link your suggestion to why it helps the environment.