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thermosetting plasics are cool |
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A '''thermosetting plastic''', also known as a '''thermoset''', is [[polymer]] material that irreversibly [[Curing (chemistry)|cures]]. The cure may be done through heat (generally above {{convert|200|C}}), through a chemical reaction (two-part [[epoxy]], for example), or [[irradiation]] such as [[electron beam processing]]. |
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Thermoset materials are usually liquid or [[malleable]] prior to curing and designed to be [[Molding (process)|molded]] into their final form, or used as [[adhesive]]s. Others are solids like that of the molding compound used in [[semiconductors]] and [[integrated circuits]] (IC). Once hardened a thermoset resin cannot be reheated and melted back to a liquid form. |
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According to [[IUPAC]] recommendation: A thermosetting polymer is a prepolymer in a soft solid or viscous state that changes irreversibly into an infusible, insoluble polymer network by curing. Curing can be induced by the action of heat or suitable [[radiation]], or both. A cured thermosetting polymer is called a thermoset.<ref>http://old.iupac.org/goldbook/TT07168.pdf</ref> |
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==Process== |
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The curing process transforms the resin into a [[plastic]] or [[rubber]] by a [[cross-link]]ing process. Energy and/or [[catalyst]]s are added that cause the molecular chains to react at chemically active sites (unsaturated or epoxy sites, for example), linking into a rigid, [[Dimension|3-D]] structure. The [[cross-link]]ing process forms a molecule with a larger molecular weight, resulting in a material with a higher [[melt]]ing 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. |
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Uncontrolled reheating of the material results in reaching the decomposition temperature before the melting point is obtained. Therefore, a thermoset material cannot be [[melt]]ed and re-shaped after it is cured. This implies that thermosets cannot be recycled, except as filler material.<ref>The Open University (UK), 2000. T838 ''Design and Manufacture with Polymers: Introduction to Polymers'', page 9. Milton Keynes: The Open University</ref> |
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==Properties== |
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Thermoset materials are generally stronger than [[thermoplastic]] materials due to this three dimensional network of bonds (cross-linking), and are also better suited to high-[[temperature]] applications up to the decomposition temperature. However, they are more brittle. Since they are "set" (non-reformable), they tend not to be recyclable. |
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==Examples== |
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Some examples of thermosets are: |
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* Polyester fibreglass systems: sheet molding compounds and bulk molding compounds) |
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* [[Polyurethane]]s: insulating foams, mattresses, coatings, adhesives, car parts, print rollers, shoe soles, flooring, synthetic fibers, etc. Polyurethane polymers are formed by combining two bi- or higher functional monomers/oligomers. |
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* [[Vulcanization|Vulcanized rubber]] |
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* [[Bakelite]], a [[phenol]]-[[formaldehyde]] resin used in electrical insulators and plasticware |
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* [[Duroplast]], light but strong material, similar to bakelite used for making car parts |
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* [[Urea-formaldehyde]] foam used in [[plywood]], particleboard and medium-density fiberboard |
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* [[Melamine resin]] used on worktop surfaces<ref>{{cite journal | author = Roberto C. Dante, Diego A. Santamaría and Jesús Martín Gil | title = Crosslinking and thermal stability of thermosets based on novolak and melamine | journal = Journal of Applied Polymer Science | year = 2009 | volume = 114 | issue = 6 | pages = 4059–4065 | doi = 10.1002/app.31114}}</ref> |
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* [[Epoxy|Epoxy resin]] used as the matrix component in many [[fiber reinforced plastic]]s such as glass-reinforced plastic and [[graphite-reinforced plastic]]) |
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* [[Polyimides]] used in printed circuit boards and in body parts of modern aircraft |
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* Cyanate esters or polycyanurates for electronics applications with need for dielectric properties and high glass temperature requirements in composites |
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* Mold or mold runners (the black plastic part in integrated circuits or semiconductors) |
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Some methods of molding thermosets are: |
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* Reactive [[injection molding]] (used for objects such as milk bottle crates) |
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* [[Extrusion molding]] (used for making pipes, threads of fabric and insulation for electrical cables) |
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* [[Compression molding]] (used to shape most thermosetting plastics) |
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* [[Spin casting]] (used for producing [[fishing lure]]s and [[jig (fishing)|jigs]], [[Miniature figure (gaming)|gaming miniatures]], [[figurine]]s, emblems as well as production and replacement parts) |
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== See also == |
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* [[Vulcanization]] |
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* [[Fusion bonded epoxy coating]] |
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* [[Thermoplastic]] |
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== References == |
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{{reflist}} |
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[[Category:Polymer chemistry]] |
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[[Category:Thermosetting plastics| ]] |
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[[ja:合成樹脂#熱硬化性樹脂]] |
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Revision as of 13:04, 7 May 2013
thermosetting plasics are cool