Plastics (polymers)

Plastics (polymers)

1. Group of materials made up of long chains of hydrogen and carbon atoms in combinations with other atoms

2. Sources of plastics

   • Animal and vegetable by-products used for semi synthetic polymers
     • cellulose mixed with acetic acid for cellulose acetate for OHP slides
     • Casein which is by-products of milk to make buttons
   • Coal, oil, gas are sources of purely synthetic plastics
     • Gained from thermal cracking and are carbon based

3. Types of plastics

   • Thermoplastics- can be reheated and remoulded
   • Thermosets- undergo a permanent change which makes them permanently rigid
   • Elastomers- have good elasticity, can be put under pressure but return to original shape after

4. Properties

   • good electrical and thermal conductors
   • good strength to weight ratio
   • good atmospheric and chemical corrosion resistance
   • low melting temp
   • lightweight
   • can be self coloured, opaque or translucent

5. Additives- materials added to the powder prior to processing (give bulk or condition the material)

   • Fillers- reduce bulk of plastic, cheaper than plastics (sawdust, wood flour, crushed quartz, limestone) they increase strength/hardness by improving brittleness
   • Flame retardants- reduce risk of combustion, they create a chemical reaction when combustion has begun, they release agents which stifle the combustion.
   • Anti-static agents- reduce effects of static charges
   • Plasticiser- improve moulding properties they reduce the softening temperature and make the plastic less brittle
   • Stabilisers- reduce effects of ultraviolet light