Polymers

- New material- 1950s

- Known as hydrocarbons- made up of carbon and hydrogen

-polymers is correct name for any plastic material

Natural: animal and vegetable by-products

-cellulose is a natural material occuring in plant fibres and is mixed with acetic acid to produce acetate

-casein is by product of milk and is used to create buttons

Synthetic: oil, coal and natural gasses

Molecule chains are held together by weak bonds which can be broken by heat.

Heat allows molecules to slide over each other

When cools the bonds reform and the platic will retain its new shape

Advantages:

Can be repeated many times

can be recycled

Example: Acrylic

Perspex is the brand name. It has similar properties of glass but it is more impact resistant. It is easily machined and is commonly used for windows and car light lenses.

Long chain molecules but held together by rigid strong crosslinks.

-Heat causes strong chemical bonds which once formed cannot be broken

-makes plastic rigid, heat resistant but not recyclable

Example: Urea- Formaldehyde

A strong plastic which is hard and brittle, it is heat resistant and is a good electrical insulator. It is used for electrical components like plugs and sockets.

Good elasticity and can be distorted under pressure but will remain to their original shape when pressure is removed.

- Long chain molecules similar properties to springs

- When material is distorted the molecules also distort and when they are released they go back to their original shape.

- Coiled molecules give the elastomers their properties.

Example: Liquid Silicon Rubber (LDR)

This is a thermosetting elastomer made up of two components mixed together before being moulded into their products. It has the ability to maintain insulation and elastomeric characteristics over a wide temperature range (50 degrees-250).

Commonly used for babies bottle teats, baking trays and spatulas, medical equipment and electrical connectors.

Advantages of plastic:

• No natural defects
• Waterproof
• Some can be recycled
• Different colours
• Strong and lightweight
• Take any shape
• Non-toxic
• Raw materials are cheap
• No finishing needed
• Non corrosive
• Easy to clean
• Good insulators of heat and electricity