- Thermosetting plastic
Thermosetting plastics thermosets) are
polymermaterials that irreversibly cure form. The cure may be done through heat (generally above 200 degrees Celsius), through a chemical reaction (two-part epoxy, for example), or irradiationsuch as electron beam processing.
Thermoset materials are usually liquid or
malleableprior to curing and designed to be molded into their final form, or used as adhesives. Others are solids like that of the molding compound used in semiconductors and integrated circuits (IC's).
The curing process transforms the resin into a
plasticor rubberby 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, 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. [The Open University (UK), 2000. T838 Design and Manufacture with Polymers: Introduction to Polymers, page 9. Milton Keynes: The Open University]
Thermoset materials are generally stronger than
thermoplasticmaterials due to this 3-D network of bonds, and are also better suited to high- temperatureapplications 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-formaldehydefoam (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)
Mold or Mold Runners(the black plastic part in Integrated Circuits (IC) or semiconductors)
Some methods of molding thermosets are:
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)
Fusion bonded epoxy coating
* [http://www.design-technology.org/lesson4b.htm A description of thermosetting plastics] http://www.polyplycomposites.com/formulas.htm
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