Thermosetting plastics (thermosets) refer to a range of polymer materials that cure, through the addition of energy, to a stronger form. The energy may be in the form of heat (generally above 200 degrees Celsius), through a chemical reaction (two part epoxy, for example), or irradiation. Thermoset materials are usually liquid or malleable prior to curing, and designed to be molded into their final form, or used as adhesive.
Thermoset polymer resins can be transformed into plastics or rubbers by cross-linking. Energy and catalysts are added that cause the molecular chains to link into a rigid, 3-D structure. A thermoset material cannot be melted and re-molded after it is cured.
Thermoset materials are generally stronger than thermoplastic materials. They are also better suited to high temperature applications. They are not easily recyclable like thermoplastics, which can be melted and re-molded.
Examples of thermosets
- Natural Rubber
- Bakelite (used in electrical insulators and plastic wear)
- Urea-Formaldehyde (used in plywood, particleboard and medium-density fibreboard)
- Melamine (used on worktop surfaces)
- Polyester Resin (used in glass-re-inforced plastics)
- Epoxy Resin (used as an adhesive and in Glass Reinforced Plastic/Fibreglass (GRP), and FRP)
Methods used to mould thermosets
- Injection Moulding (used for objects like milk bottle crates)
- Extrusion Moulding (used for making pipes, threads of fabric and insulation for electrical cables)
- Calendering (used for making large sheets of plastic)
- Compression Moulding (used to shape most thermosetting plastics)