Thermoset materials

Thermoset materials (phenolics) are polymers in which the crosslinking reaction of the macromolecules only takes place during processing and shaping. They are mostly manufactured through the process of polycondensation.

Thermoset materials are usually supplied as moulding compounds comprising synthetic resins and fillers in powder form, or as granulates or pastes. Compounds that are suitable for chemical curing will also include an additive (also referred to as an oxidising agent or hardener). Intermediates such as resin impregnated laminates (sheet moulding compounds, or SMCs) and glass-fibre reinforced compounds (bulk moulding compounds, or BMCs) will already contain the hardener.

Thermoset materials are plasticised, can be mixed if necessary, and are usually shaped under pressure. Compounds containing chemical hardeners will then harden in the mould, their macromolecules Forming linear and crosslinked three-dimensional structures. Other thermoset materials are hardened by the application of heat or radiation (often UV light).

Once cured, thermoset materials are hard and glassy with molecules that are firmly and three-dimensionally crosslinked via primary valency bonds. This crosslinking is irreversible.

Thermoset materials are used in casings, protective enclosures, circuit breakers, bodywork parts and fibrous composite materials.

Types of thermoset materials include:

• Phenolic and cresol resins (PF)
• Melamine resin (MF)
• Urea resin (UF)
• Polyester resin (UP)
• Epoxy resin (EP)