termosets

Thermosets, also known as termosets in some languages, are a class of polymer materials that irreversibly cure to form a rigid, crosslinked network. Unlike thermoplastics, which soften upon heating, thermosets do not remelt after curing. The crosslinking is typically achieved by chemical reactions such as addition (e.g., epoxy-amine) or condensation (e.g., phenolic resins) and results in insoluble, infusible materials with high thermal and chemical resistance.

Curing can be initiated by heat, chemical catalysts, or UV/light. The cure process may be exothermic and can be accelerated by catalysts. Once fully cured, the network structure locks in the material’s dimensions and properties. Crosslink density influences stiffness, temperature resistance, and toughness.

Common thermoset families include epoxies, phenolics, unsaturated polyesters, vinyl esters, cyanate esters, silicones, and polyurethane systems. They are processed by molding, casting, or reinforcement in composites (such as fiber-reinforced polymers) via methods like compression molding, transfer molding, or resin transfer molding.

Properties and limitations: high heat resistance, chemical resistance, dimensional stability, and low creep at elevated temperatures. They are typically more brittle than thermoplastics and may have lower toughness and impact resistance. They cannot be remelted or recycled by melting; recycling often involves mechanical grinding or chemical recycling but is challenging and energy-intensive.

Applications include protective coatings, adhesives, electronic potting and encapsulation, aerospace and automotive components, and fiber-reinforced composites. Environmental concerns include curing exotherms, VOCs from resins, and end-of-life disposal.