Plastics
Sources of plastics
Natural
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.
| Name | Properties | Principal uses |
|---|---|---|
| Polyamide (Nylon) | Creamy colour, tough, fairlyhard, resists wear, self-lubricating, good resistance to chemicals and machines | Bearings, 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 well | Signs, covers of storage boxes, aircraft canopies and windows, covers for car lights, wash basins and baths |
| Polypropylene | Light, hard but scratches easily, tough, good resistance to chemicals, resists work fatigue | Medical equipment, laboratory equipment, containers with built-in hinges, 'plastic' seats, string, rope, kitchen equipment |
| Polystyrene | Light, hard, stiff, transparent, brittle, with good water resistance | Toys, especially model kits, packaging, 'plastic' boxes and containers |
| Low density polythene (LDPE) | Tough, good resistance to chemicals, flexible, fairly soft, good electrical insulator | Packaging, especially bottles, toys, packaging film and bags |
| High density polythene (HDPE) | Hard, stiff, able to be sterilised | Plastic bottles, tubing, household equipment |
Thermoset plastics can only be heated and shaped once.
Properties and uses of the thermoset plastics.
| Name | Properties | Principal uses |
|---|---|---|
| Epoxy resin | Good electrical insulator, hard, brittle unless reinforced, resists chemicals well | Casting and encapsulation, adhesives, bonding of other materials |
| Melamine formaldehyde | Stiff, hard, strong, resists some chemicals and stains | Laminates for work surfaces, electrical insulation, tableware |
| Polyester resin | Stiff, hard, brittle unless laminated, good electrical insulator, resists chemicals well | Casting and encapsulation, bonding of other materials |
| Urea formaldehyde | Stiff, hard, strong, brittle, good electrical insulator | Electrical fittings, handles and control knobs, adhesives |
