Thermoset

Thermoset polymers, or thermosetting plastics, are polymers that irreversibly cure to form a rigid, crosslinked network. They begin as a viscous liquid or gel and, upon heating, cooling, or exposure to a curing agent, undergo a chemical reaction that creates a three-dimensional structure. Once cured, they do not remelt or reprocess by heating in the same way as thermoplastics.

Common thermosets include epoxies, phenolic resins, unsaturated polyesters, polyurethanes, silicones, and bismaleimide resins. The curing process can involve condensation or addition reactions and may require catalysts, hardeners, or curing agents. Processing methods include casting, compression molding, transfer molding, resin infusion, and composite layups, often followed by a post-cure heat treatment to enhance properties.

Thermosets are valued for their high modulus and strength, excellent thermal and chemical resistance, and good dimensional stability and electrical insulation. They typically exhibit high heat resistance and structural rigidity. However, they tend to be more brittle than many thermoplastics and can have lower impact toughness. Their crosslinked networks make repair, reshaping, and recycling challenging, limiting reprocessing options compared with thermoplastics.

Applications span coatings, adhesives, electrical potting and encapsulation, and structural composites used in aerospace, automotive, and electronics. Thermosets are also employed in protective coatings, sealants, and insulation materials, where durability and heat resistance are advantageous.

Recycling and disposal are ongoing considerations. Once cured, most thermosets cannot be melted and remolded; recycling methods focus on mechanical recovery as fillers, chemical recycling for certain chemistries, or energy recovery through waste-to-energy processes. Environmental and safety considerations include managing curing agents and emissions.