Ceramics, Polymers & Composites (AQA GCSE Chemistry)

• Ceramics are non-metal solids with high melting points 
• They have widely used in construction materials and domestic appliances

Types of poly(ethene)

• The properties of a polymer depends on:
  • The monomers it is made from 
  • The conditions under which the polymer is made 
• Ethene can form high density (HD) poly(ethene) and low density (LD) poly(ethene)
• Low density poly(ethene) is made at high pressure and moderate temperature 
  • This is used for bags and bottles where flexibility is needed
• High density poly(ethene) is produced at lower temperatures and pressures and with the use of a catalyst
  • This polymer has a more rigid, solid structure and is used to produce water tanks, mouldings and drain pipes 

Thermosoftening and thermosetting polymers

• Polymers can also be divided into thermosoftening and thermosetting polymers
• Thermosetting polymers consist of chains which have strong cross-links between them
  • These polymers are strong and rigid structures that don’t melt when they are heated because lots of energy would be required to overcome the cross-links
  • They are commonly used in electrical plugs
• Thermosoftening polymers consist of individual, tangled chains with no cross-links between them
  • These polymers therefore have low melting points, can be melted and remoulded to form different shapes
  • They are commonly used to make packaging and plastic bottles

The structures of thermosetting and thermosoftening polymers

Thermosetting polymers have crosslinks between polymer chains, unlike thermosoftening polymers

• Composites are made from two components: reinforcement and matrix
• The reinforcement material is embedded in the matrix material which acts as a binder
• Common examples include:
  • Fibreglass 
  • Concrete
  • Carbon fibres
• Wood is an example of a natural composite
• The properties of composites depend on the reinforcement and matrix used so composites can be tailor engineered to meet specific needs
• For example, carbon fibres for example are extremely strong and low weight so used they are used in aviation, aeronautics and for making professional racing bicycles
• Steel reinforced concrete has immense tensile and compressive strength allowing it to be used as columns and supporting structures in construction

Composite	Reinforcement	Matrix	Properties
concrete	aggregate (sand and gravel)	cement	strong
fibreglass	glass fibres	polymer resin	low density and strong
carbon fibre	carbon fibres / carbon nanotubes	polymer resin	strong and light
wood	cellulose fibres	organic polymer

Diagram of concrete