thermoset adj : having the property of becoming permanently hard and rigid when heated or cured; "the phenol resins and plastics were the original synthetic thermosetting materials" [syn: thermosetting] [ant: thermoplastic]

English

Noun

1. A thermosetting plastic

Thermosetting plastics (thermosets) are polymer materials that irreversibly cure, to a stronger form. The cure may be done through heat (generally above 200 degrees Celsius), through a chemical reaction (two-part epoxy, for example), or irradiation such as electron beam processing.

Thermoset materials are usually liquid or malleable prior to curing and designed to be molded into their final form, or used as adhesives.

The curing process transforms the resin into a plastic or rubber by a cross-linking process. Energy and/or catalysts are added that cause the molecular chains to react at chemically active sites (unsaturated or epoxy sites, for example), linking into a rigid, 3-D structure. The cross-linking process forms a molecule with a larger molecular weight, resulting in a material with a higher melting point. During the reaction, when the molecular weight has increased to a point so that the melting point is higher than the surrounding ambient temperature, the material forms into a solid material.

Uncontrolled reheating of the material results in reaching the decomposition temperature before the melting point is obtained. Therefore, a thermoset material cannot be melted and re-shaped after it is cured. This implies that thermosets cannot be recycled, except as filler material.

Thermoset materials are generally stronger than thermoplastic materials due to this 3-D network of bonds, and are also better suited to high-temperature applications up to the decomposition temperature of the material.

Some examples of thermosets are:

• Vulcanized rubber
• Bakelite, a phenol-formaldehyde resin (used in electrical insulators and plasticware)
• Urea-formaldehyde foam (used in plywood, particleboard and medium-density fibreboard)
• Melamine resin (used on worktop surfaces)
• Epoxy resin (used as an adhesive and in fibre reinforced plastics such as glass reinforced plastic and graphite-reinforced plastic)
• Polyimides (used in printed circuit boards and in body parts of modern airplanes)

Some methods of molding thermosets are:

• Reactive injection molding (used for objects like milk bottle crates)
• Extrusion molding (used for making pipes, threads of fabric and insulation for electrical cables
• Compression molding (used to shape most thermosetting plastics)
• Spin casting (used for producing fishing lures and jigs, gaming miniatures, figurines, emblems as well as production and replacement parts)

See also

• Thermoplastic
• Vulcanization
• Fusion bonded epoxy coating
• Plastic

External links

• A description of thermosetting plastics