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Design & Technology

Materials

Plastics

Sources of plastics

Natural

Two yellow rubber ducks (actually made from plastic) floating on soapy water.

Natural sources of plastics include:

  • plants - from which cellulose can be extracted
  • trees - from which latex, amber and resin can be extracted
  • animals - from which horn and milk (used to make glues) are obtained
  • insects - from which shellac (used to make polish) is obtained

Synthetic

Synthetic plastics are chemically manufactured from:

  • crude oil
  • coal
  • natural gas

Thermoplastics and thermoset plastics

Plastics are divided into thermoplastics and thermoset plastics.

Thermoplastics can be heated and shaped many times.

Properties and uses of thermoplastics.

NamePropertiesPrincipal uses
Polyamide (Nylon)Creamy colour, tough [tough: Able to withstand blows or sudden shocks without breaking. ], fairly hard [hard: Able to resist wear, scratching and indentation. ], resists wear, self-lubricating [lubricating: Oiling or reducing friction. A lubricant is anything which reduces the friction between two surfaces. ], 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, brittlebrittle: If something is brittle it is easily broken. in small sections, good electrical insulatorinsulator: Material that is a poor conductor of electricity or heat., 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 fatigue [work fatigue: Weakening of a material as a result of prolonged or repeated stress on it. ]Medical 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

Thermoset plastics can only be heated and shaped once.

Properties and uses of the thermoset plastics.

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 resinStiff, hard, brittle unless laminated, 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

Back to Resistant materials index

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