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thermosets
Related:
Organic Chemistry
materials that can not be softened on heating. In thermosetting
polymers, the polymer chains are joined (or cross-linked) by
intermolecular bonding. Thermosets are usually supplied as partially
polymerized or as monomer-polymer mixtures. Cross-linking is
achieved during fabrication using chemicals, heat, or radiation;
this process is called curing or vulcanization.
Thermosets are also used in some forms of plastics processing,
including fibre-reinforced composites, and are the most common resins in
formulated products like paints, adhesives, and inks. Examples include
phenol formaldehyde,
urea formaldehyde, epoxy, polyurethane,
unsaturated
polyester, alkyd, and silicone. These resins are cured via a chemical
reaction which is generally not reversible. Whereas thermoplastics
soften and can be reprocessed using heat, thermosets generally undergo
decomposition when heated. For this reason, recycling of thermosets is
difficult. |
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