Uses and Environmental Issues of Polymers

This page covers content standard 12.4 of the Form 5 Polymers chapter: uses and environmental issues of polymers. Having learned what polymers are and how they are made, you now weigh their benefits against their costs. The exam asks you to link uses to properties, to explain why plastics are an environmental problem, and to suggest ways to reduce that problem. This standard often appears as a structured or essay-style question, so clear reasoning matters.

Uses linked to properties

Synthetic polymers have replaced many traditional materials because they combine several useful properties: they are light, strong, cheap to make, waterproof, resistant to chemicals, durable, good electrical and heat insulators, and easily moulded into any shape. The key skill is to link each use to a property.

Polymer	Use	Property that makes it suitable
Polythene	Plastic bags, films	Light, flexible, waterproof
PVC	Pipes, cable insulation	Tough, waterproof, good insulator
Polypropene	Containers, ropes	Strong, resistant to chemicals
Polystyrene	Packaging, disposable cups	Light, good heat insulator
Nylon	Ropes, fishing line, textiles	Strong, hard-wearing
Perspex	Windows, lenses	Transparent, does not shatter easily

When you answer a “why is this polymer used for X” question, always name the property, not just the use.

Why polymers harm the environment

The very properties that make plastics useful, durability and resistance to attack, also make them a problem when they are thrown away.

• Non-biodegradable. Most synthetic polymers are non-biodegradable: microorganisms cannot break them down. They therefore remain in the environment for a very long time.
• Accumulation of waste. Because they do not rot, plastics pile up as litter and fill up landfill sites. Discarded plastic can block drains, and plastic in rivers and the sea harms aquatic life when animals swallow it or become trapped.
• Toxic gases from open burning. Burning plastic in the open is not a safe solution. Incomplete combustion releases carbon monoxide (CO), a toxic gas; complete combustion still produces carbon dioxide (CO₂), a greenhouse gas; and burning PVC releases hydrogen chloride (HCl), an acidic, corrosive gas, along with other harmful substances.

Ways to reduce the problem

You should be able to suggest sensible steps, often remembered as the three Rs:

• Reduce, use fewer plastic items; for example, bring your own bag instead of taking new plastic bags.
• Reuse, use containers and bottles again rather than throwing them away after one use.
• Recycle, collect and reprocess plastics into new products, saving raw materials and reducing waste.
• Use biodegradable or photodegradable polymers, newer plastics that can be broken down by microorganisms or by sunlight.
• Dispose of plastics properly, send them to controlled facilities rather than burning them in the open or dumping them.

Worked example

Question. A piece of polythene is burned completely. The repeating unit of polythene is, CH₂, CH₂, (formula C₂H₄), and it burns according to: C₂H₄ + 3O₂ → 2CO₂ + 2H₂O. Calculate the volume of carbon dioxide, measured at room conditions, produced when 14 g of polythene undergoes complete combustion. [Relative atomic masses: H = 1, C = 12; molar volume of gas = 24 dm³ mol⁻¹]

Step 1, Find the Mr of the repeating unit.

Mr of C₂H₄ = (2 × 12) + (4 × 1) = 24 + 4 = 28

Step 2, Find the moles of repeating units burned.

moles = mass ÷ Mr = 14 g ÷ 28 g mol⁻¹ = 0.5 mol

Step 3, Use the equation ratio. From C₂H₄ + 3O₂ → 2CO₂ + 2H₂O, 1 mol of C₂H₄ gives 2 mol of CO₂, so:

moles of CO₂ = 0.5 × 2 = 1.0 mol

Step 4, Convert moles of CO₂ to a volume. Using the molar volume, 24 dm³ mol⁻¹ (= 24 dm³ mol⁻¹) at room conditions:

volume = moles × molar volume = 1.0 mol × 24 dm³ mol⁻¹ = 24 dm³

Answer. Complete combustion of 14 g of polythene produces 24 dm³ of carbon dioxide at room conditions. Note that in the open air, incomplete combustion would also release toxic carbon monoxide, which is why open burning of plastic is discouraged.

Practice question

Question. Synthetic polymers such as plastic bags are causing serious waste problems in Malaysia. (a) Explain why these polymers remain in the environment for a long time. (b) State why open burning is not a good way to get rid of them. (c) Suggest two ways to reduce plastic waste.

Answer. (a) The polymers are non-biodegradable, microorganisms cannot break them down, so they do not rot and stay in the environment for a very long time. (b) Open burning releases toxic gases such as carbon monoxide, and burning PVC gives off acidic hydrogen chloride, polluting the air. (c) Any two of: reduce the use of plastic (e.g. reusable bags), reuse containers, recycle plastics, or use biodegradable polymers.

Exam tip

For a “uses” question, always pair the use with the property that justifies it, for example, “PVC is used for pipes because it is tough and waterproof.” For an “environmental” question, the single most important word is non-biodegradable, and you should be able to define it. When asked about burning, name the actual harmful gases, carbon monoxide (toxic), carbon dioxide (greenhouse gas) and, for PVC, hydrogen chloride (acidic), rather than saying vaguely that it “makes pollution.” Finish with concrete reduce, reuse, recycle measures. In Paper 2 essay questions, a clear structure, uses with properties, problems with reasons, then solutions, earns marks steadily.

Where this fits

This is content standard 12.4 of the Polymers chapter, and it closes the chapter by applying everything to real life. The synthetic polymers you weigh up here, polythene, PVC, polypropene, are the same ones introduced in natural and synthetic polymers (12.1) and made by the polymerisation you studied in 12.2. Practise the combustion calculation and the essay structure on the chapter worked examples page, and check the exact wording for environmental answers on the common mistakes page. In our online 1-to-1 SPM Chemistry lessons, taught in English from RM50/hr, a one-to-one teacher can help you structure the Paper 2 essay so that uses, problems and solutions each score.

Quick recap

• Synthetic polymers are used because they are light, strong, cheap, waterproof, durable and easily moulded, link each use to a property.
• The main problem is that most plastics are non-biodegradable, so they accumulate as waste.
• Open burning releases carbon monoxide (toxic), carbon dioxide (greenhouse gas) and, from PVC, hydrogen chloride (acidic).
• Manage waste by reduce, reuse, recycle, using biodegradable polymers and disposing of plastics properly.