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Plastics - or polymers - fall into two main groups: Thermo and Thermoset plastics, a third group is called Elastomers.
Thermoplastics 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 moulded 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 moulding
Rotational moulding
Extrusion
Vacuum forming
Compression moulding
Details of these processes can be found in the technology file in the TEP CD VR files. See also materials selection and processes and Resistant materials 2, also in the Technology folder.
Thermo plastics include:
Name
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Properties
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Applications and Uses
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ABS- Acrylonitrile-butadiestryrene
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Strong, tough, hard, chemical resistant, durable. All process.
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Dash boards and car trim, toys, phones, handles, electrical products.
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Nylon ( polyamide)
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Tough, hard, light, self lubricating, chemical resistant, machines well, extrudable, injects well.
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Bearings, gears, rope, hinges and catches, engineering applications.
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Acetate - cellulose
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Tough stiff and hard, transparent and light, heat resistant.
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Tool handles, pen bodies, frames for glasses. Can be injection moulded.
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Acrylic- polymethlacrilate
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stiff, durable, insulator, machines well, polishes well scratches easily
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Car light covers, baths, shower trays, basins. can be line bent/vac formed/injection moulded with ease.
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Polypropylene
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Tough, light, chemical resistant.. Will scratch, quite soft.
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Containers, pots, plastic seats, ropes, nets. Very versatile.
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Polystyrene
expanded-
high impact-
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light, stiff, transparent, brittle, waterproof/resistant.
very light
very tough
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toys, electrical product cases, boxes
packaging
vacuum formings
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Polythene
Low density
High density
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Tough, flexible, soft, insulator, chemical resistant.
Hard, stiff.
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Packaging, bags,
tube, bottles, domestic appliances.
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PVC- Polyvinyl chloride
uPVC
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Stiff hard tough light
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cables and hoses sheet fabric
Gutters windows extrusions
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Thermoset plastics differ in that they are not re-mouldable. Strong cross links are formed during the initial moulding process that give the material a stable structure. They are more likely to be used in situations where thermal stability is required. They tend to lack tensile strength and can be brittle.
Name
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Properties
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Applications and Uses
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Urea formaldehyde
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Strong, insulator, brittle, hard, stiff.
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Electrical fittings. Handles and knobs
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Polyester resin
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Liquid raw state, stiff hard, insulator, chemical resistance, brittle without fibre reinforcement.
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Casting, bonding fibres- glass, Kevlar, carbon fibre.
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Epoxy resins-trade names include araldite.
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Good insulator, brittle chemical resistant.
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adhesives, bonding fibres, encapsulation.
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Melamine formaldehyde
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Hard, strong, heat resistant.
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adhesives, bonding fibres, encapsulation.
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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 plastic. These can include:
Stabilisers to prevent degradation due to moisture or UV light.
Lubricants such as sulphides and waxes to make the polymer easier to
form and self lubricating in use.
Pigments - often referred to as 'master batch' adding colours to the plastic.
Plasticisers - added to make the plastic les 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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