Give three examples of synthetic plastics
- Polypropylene – used in buckets, rope, clothing and chairs.
- Polycarbonate – a rigid and hard plastic used instead of glass and aluminium, because of its impact resistance.
- Polyester – used widely in the clothing industry. A versatile fabric which is combined with nylon.
How are synthetic plastics developed into products?
- Crude oil is extracted from the seabed.
- Oil is heated in a fractioning tower, and broken down into chemicals. - Chemicals are used to make plastic.
- Heat and pressure are applied to the plastic to shape it.
- Product is made.
Monomers combine to form chains of molecules called polymers. What happens as a polymer grows?
Its melting point increases and it becomes more rigid because of the links between each monomer molecule.
Describe thermoplastics
- They are mostly recyclable.
- They can be shaped and reshaped on the heat.
- They have plastic memory.
- They are made of a long polymer chains that have few cross links making them flexible under heat.
Describe thermosetting plastics
- They are initially set by heat.
- They cannot be reshaped once set.
- They are extremely durable and strong.
- They are common in powder or resin forms.
- They consist of polymer chains with the strong bonds between each chain. This is more a more rigid structure than a thermoplastic and heat improves the strength of the links.
Name three thermoplastics
- High density polythene
- Polypropylene
- Acrylic
Name three thermosetting plastics
- Epoxy resin
- Urea formaldehyde
- Phenol formaldehyde.
Name three stock forms of plastic
Powder, granules and sheets.
Name three additives and how they change the properties of a plastic
- Pigments – add colour to plastic.
- Plasticisers – make plastic less brittle and hard.
- Lubricants – improve the flowing quality making it easier to form.
When is vacuum forming used?
When identical products need to be mass produced.
How does injection moulding work?
This involves heating plastic granules to their melting point and then injecting them at high pressure through a nozzle into a mould.
How does blow moulding work?
This involves a mould closing and sealing a thin plastic tube called a parison. It also cuts to the required length.
Why do plastics require little to no surface finish?
They are self finishing and have excellent surface qualities.
Give three examples of natural plastics
Shellac – a resin produced by trees, used as a varnish and die.
Rosin – used as a resin to give grip to the bow of a string instrument such as a violin.
Bitumen – used as waterproof rendering for houses, roads and boats.
