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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.

Thermo plastics include:



Applications and uses


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


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.

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.



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

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