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Thermoplastics and Thermosetting plastics
Plastics – or polymers – fall into two main groups: a Thermo and Thermoset plastic, a third group is called Elastomers.
Thermo plastics can be made ‘plastic’ and malleable at high temperatures. Modern thermo plastic polymers melt any where between 65 degrees C and 200+ degrees C. In this state they can be molded in a number of ways: They differ from thermo set plastics in that they can be returned to this plastic state by reheating. They are then fully recyclable.
These include: Injection molding, Rotational molding, Extrusion, Vacuum forming, and Compression molding.
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| Thermo plastics include: |
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Name |
Properties |
Applications and uses |
ABS-Acrylonitrile-butadiestryrene |
Strong, tough, hard, chemical resistant, durable. All process. |
Dashboards and car trim, toys, phones, handles, electrical products. |
Nylon- polyamide |
Tough, hard, light, self-lubricating, chemical resistant, machines well, extrudible, injects well. |
Bearings, gears, rope, hinges, and catches, engineering applications. |
Acetate- cellulose |
Tough, stiff and hard. Transparent and light weight, heat resistant |
Tool handles, pen bodies, frames for glasses. Can be injection molded. |
Acrylic- polymethlacrilate |
Stiff, durable, insulator, machines well, polishes well. Scratches easily. |
Car light covers, baths, shower trays, basins. Can be line bent/vacuum formed, injection molded with ease |
Polypropelene |
Tough, light weight, chemical resistant. Will scratch, quite soft. |
Containers, pots plastic seats, ropes, nets. Very versatile. |
Polystyrene – expanded – high impact |
Light weight, stiff, transparent, brittle, waterproof/resistant. Very light, very tough |
Toys, electrical product cases, boxes, packaging. |
Polythene – low density – high density |
Tough, flexible, soft, insulator, chemical resistant |
Packaging, bags, tube, bottles, domestic appliances |
PVC – polyvinyl chloride |
Stiff, hard, tough, light weight |
Cables and hoses, sheet fabric, gutters, windows, and extrusions. |
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| Thermoset plastics differ in that they are not re-moldable. Strong cross links are formed during the initial molding process that gibe the material a stable structure. They are more likely to be used in situations where thermal stability is required. |
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Name |
Properties |
Applications and Uses |
Urea formaldehyde |
Strong, insulator, brittle, hard, and stiff |
Electrical fittings. Handles and knobs |
Polyester resin |
Liquid raw state, stiff, hard, insulator, chemical resistance, brittle without fiber reinforcement |
Casting, bonding fibers with glass, Kevlar, carbon fiber |
Epoxy resins – trade names include araldite. |
Good insulator, brittle chemical resistant |
Adhesives, bonding fibers, encapsulation. |
Melamine formaldehyde |
Hard, strong, heat resistant |
Adhesives, bonding fibers, encapsulation |
| Phenolics |
Heat resistent, electrical properties, stiff, strong, outstanding durability, water resistent, corrosion resistent |
thermal insulation, sound dampening, electrical components, lighting components, automotive |
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Elastomers are a small group of polymers that display stretching and deforming at room temperatures – elastic and rubbers are examples of this group.
Additives are used in both forms of plastics. These can include:
- Stabilizers to prevent degradation due to moisture or UV light
- Lubricants such as sulphides and waxes to make the polymer easier to form
- Self-lubricating in use
- Pigments – often referred to as ‘master batch’, add colors to the plastic
- Plasticisers – added to make the plastic less hard or brittle
- Fillers – these can be added to enhance properties such as wear, strength, toughness, durability and talc and clay may be used to bulk out the plastic reducing costs.
- Flame retardants – to prevent combustion in materials such as domestic foams
- Blowing agents – to permit foams to be blown
- Anti – static agents – used to prevent the build up of electrical charge
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