Chem Chp 21.4-21.5

Why are plastics used?

Relatively cheap

Easily moulded into various shapes

Light, tough, and waterproof

Durable (resistant to decay, rusting and chemical attack)

What does it mean when plastics are non-biodegradable

It means that they cannot be broken down by bacteria and other living organisms in the soil, so it is very hard to dispose plastics after they are used.

What are the environmental problems caused by the disposal of plastics?

Land pollution - Plastics do not decompose, so burying plastics in landfills leads to an increasing amount of built-up waste

Water pollution - Plastic in the sea can endanger sea animals, as it can be mistaken for food and be choked on. Plastics also clog up rivers and drains, which might be breeding grounds for mosquitoes

Air pollution - Plastics are mostly flammable, so when they are incinerated, poisonous gases are produced. e.g. PVC produces corrosive hydrogen chloride gas (acidic) on combustion

What are the 2 ways to recycle plastics?

Physical method

Chemical method

Before recycling occurs, what must happen? And why?

Pre-treatment of plastic, as not all plastics can be recycled

What does pre-treatment of plastic waste involve?

1) Sorting by different methods (e.g. manual sorting, sorting by density)

2) Washing to remove contaminants

3) Shredding or grinding into smaller pieces

In the physical method of recycling plastics (mechanical recycling), …

the chemical composition of the recycled plastic remains unchanged

What happens in mechanical recycling?

After pre-treatment, small pieces of plastics like poly(ethene) are melted, cooled, pulled into long, thin strands, and cut into pellets, which can be made into new products.

In the chemical method of recycling plastics, …

plastic waste is converted into different raw materials through different chemical reactions