Thermosoftening plastics and thermosetting plastics

There are two main categories of plastic:

  • Thermosoftening (also called thermoplastics) are plastics which will soften when heated and can be reshaped.
  • Thermosetting plastics are plastics do not soften on heating. They are used when resistance to heat is important (eg kettles, plugs, laptop chargers etc).

The properties and uses of some common thermosoftening plastics are shown in the table below.

NamePropertiesPrincipal uses
Polyamide (Nylon)Creamy colour, tough, fairly hard, resists wear, self-lubricating, good resistance to chemicals and machinesBearings, gear wheels, casings for power tools, hinges for small cupboards, curtain rail fittings and clothing
Polymethyl methacrylate (Acrylic)Stiff, hard but scratches easily, durable, brittle in small sections, good electrical insulator, machines and polishes wellSigns, covers of storage boxes, aircraft canopies and windows, covers for car lights, wash basins and baths
PolypropyleneLight, hard but scratches easily, tough, good resistance to chemicals, resists work fatigueMedical equipment, laboratory equipment, containers with built-in hinges, 'plastic' seats, string, rope, kitchen equipment
PolystyreneLight, hard, stiff, transparent, brittle, with good water resistanceToys, especially model kits, packaging, 'plastic' boxes and containers
Low density polythene (LDPE)Tough, good resistance to chemicals, flexible, fairly soft, good electrical insulatorPackaging, especially bottles, toys, packaging film and bags
High density polythene (HDPE)Hard, stiff, able to be sterilisedPlastic bottles, tubing, household equipment

The properties and uses of some common thermosetting plastics are shown in the table below.

NamePropertiesPrincipal uses
Epoxy resinGood electrical insulator, hard, brittle unless reinforced, resists chemicals wellCasting and encapsulation, adhesives, bonding of other materials
Melamine formaldehydeStiff, hard, strong, resists some chemicals and stainsLaminates for work surfaces, electrical insulation, tableware
Polyester resinLaminated, good electrical insulator, resists chemicals wellCasting and encapsulation, bonding of other materials
Urea formaldehydeStiff, hard, strong, brittle, good electrical insulatorElectrical fittings, handles and control knobs, adhesives