What is a thermoset?
A thermoset (also called a thermosetting plastic or duroplast) is a plastic that forms a fixed, three-dimensional network of molecules as it cures, and afterwards no longer melts or softens when heated. Curing happens through a chemical reaction, for example after mixing a resin with a hardener, or through heat. The process is irreversible. When strongly heated, a thermoset decomposes or chars instead of melting.
Examples and uses in construction
- Epoxy resin: adhesives, poured resin floors, concrete repair, crack injection and chemical anchors.
- Unsaturated polyester: glass-fibre reinforced polyester (GRP) for roof coverings, gutters, dormers and rooflights.
- Polyurethane (PUR) and PIR: most PUR foam and PIR insulation boards are thermosets.
- Phenolic and melamine resins: phenolic foam insulation, HPL sheet material and the glue in some wood-based boards.
Properties
- Hard, dimensionally stable and resistant to heat and many chemicals.
- Shows little creep under sustained load.
- Cannot be remelted or welded: a damaged part is repaired with a new layer of resin, not by heating.
- Harder to recycle than a thermoplastic, because the material cannot be melted down.
Working tips
- Stick exactly to the mixing ratio of resin and hardener. Too much or too little hardener gives a soft or brittle result.
- Note the working time (pot life) and the minimum application temperature on the packaging.
- Wear gloves and ensure ventilation: epoxy in particular can cause skin sensitisation on contact.
Related terms
- Thermoplastic
- Plastic
- Epoxy adhesive
- Polyester
- Resin
- Glass-fibre reinforced polyester
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