Ceramics, Composites and Polymers as Materials — AQA GCSE Chemistry (Separate)
Different materials have different properties that make them suitable for particular uses.
Polymers
The properties of a polymer depend on the monomers used and the conditions under which it is made. For example, ethene can form:
- Low density (LD) poly(ethene) — made at high pressure; flexible, used for bags and films.
- High density (HD) poly(ethene) — made with a catalyst at lower temperature/pressure; more rigid.
Thermosoftening polymers melt when heated and can be remoulded (chains held by weak intermolecular forces). Thermosetting polymers have cross-links between chains, so they do not melt when heated.
Ceramics
Ceramics include glass and clay ceramics:
- Soda-lime glass is made by heating sand, sodium carbonate and limestone.
- Borosilicate glass is made from sand and boron trioxide and melts at a higher temperature.
- Clay ceramics (e.g. pottery, bricks) are made by shaping wet clay and then firing it at a high temperature.
Ceramics are generally hard, brittle and insulators.
Composites
A composite is made of two materials: reinforcement (fibres or fragments) held in a matrix (binder). Examples: fibreglass, carbon fibre, concrete and wood. Composites combine the useful properties of both materials.
Exam tips
- Polymer properties depend on monomers and reaction conditions (LD vs HD poly(ethene)).
- Thermosoftening = remeltable; thermosetting = cross-linked, doesn't melt.
- Ceramics (glass, clay) are hard, brittle insulators.
- A composite = reinforcement + matrix (e.g. fibreglass, concrete).