Plastics

Plastics are materials made from polymers. A polymer is a very long chain built from many small, repeating molecules called monomers. Think of snapping lots of identical paperclips into one long chain.

Monomers, polymers, and how plastics form

Addition polymerisation: many small alkene molecules (like ethene) join to make one long chain, for example poly(ethene) used in bags and bottles.

Condensation polymerisation: two different monomers join and a small molecule (often water) is removed each time. PET (a polyester used in drink bottles) is made this way.

Note: Plastics are usually synthetic (made by people). Natural polymers also exist, like proteins in your body.

Useful properties of plastics

• Lightweight but strong (good for packaging)
• Waterproof and do not corrode
• Electrical insulators (safe cable coatings)
• Easily moulded when soft to many shapes

Disposal and environmental challenges

• Landfill: many plastics are not biodegradable, so they stay in the ground for a very long time, taking up space.
• Oceans: plastic waste can trap animals or be eaten by them; it can break into tiny pieces called microplastics.
• Burning: can produce toxic and acidic gases that harm health and the environment.

Recycling and PET

Plastics can be recycled by melting and reshaping (works best for many thermoplastics). PET is special because it can also be chemically turned back into its monomers and then re-polymerised to make new PET. This is called chemical recycling.

Smart use

• Reduce: use fewer single-use plastics
• Reuse: refill bottles and bags
• Recycle: check symbols; not all plastics are accepted

Common misconceptions

• “All plastics are recyclable” – different types need different methods; some are hard to recycle.
• “Biodegradable plastic disappears quickly” – many need special conditions and do not break down in the ocean.
• “Burning solves the problem” – it can release harmful gases.