What is a Thermoset?
Thermosets are synthetic composites or plastics that strengthen when heated, yet cannot successfully be remolded, shaped, or reheated after initial heat forming or molding. Thermoset molded parts remain dimensionally stable within elevated temperatures and electrical environments. The material properties of thermosets give molded parts a resistance to corrosion, UV exposure, and aggressive chemicals such as oils and automotive fluids. These properties make thermosets an ideal material choice for part assemblies exposed to electrical current, outdoor elements and automotive applications. In electrical applications, thermoset molded components have strong electrical insulation and dielectric strength and resistance to electrical arc and track, protecting the integrity of molded parts and assemblies.
Thermoset materials include Bulk Molding Compound (BMC), Phenolic, Epoxy, and Diallyl Phthalate (DAP). Bulk Molding Compounds or BMCs are unsaturated polyesters and vinyl esters. These materials can be injection, compression, injection-compression, or transfer molded. The main molding or processing difference between thermosets and thermoplastics is that thermosets are molded into a preheated or hot mold at around 350F. The thermoset resin meeting the hot mold causes a chemical reaction, and gives the molded part its strong end properties. A thermoplastic on the other hand is molded into a cooled mold to form the molded parts, and does not offer the same stability thermosets offer in its molded properties.
Understanding Thermoset Plastics
With an array of material property benefits, molded thermoset parts are used in a variety of customer end-markets and applications that require a strong, durable material capable of withstanding aggressive elements. Thermosets will not degrade with exposure to certain chemicals, oils, and automotive fluids. In electrical applications and assemblies, thermoset parts protect internal components with superior dielectric strength and electrical insulation. In outdoor applications, thermoset components remain durable even in wide-ranging weather conditions including exposure to heavy sunlight and UV, rain, sleet or snow. Whether a product application functions in Alaska or Arizona, thermosets remain a preferred material choice of engineers and designers for challenging applications requiring heat-stable components. Economically, the price per lb. for thermosets are very competitive against similarly performing engineered thermoplastics.
In scientific terms, a thermoset monomer must have three or more reactive ends, with its molecular chains crosslinking in three dimensions. Post-molding, thermosets have virtually all molecules interconnected with strong, permanent, physical bonds which are not heat reversible. Thermoplastic monomers on the other hand, only have two reactive ends for linear chain growth.
In layman terms, molding or curing a thermoset is like cooking an egg or baking a cake. Once an egg is dropped into boiling water and cooked, it cannot revert to its original physical state as a yoke. Similarly, after thermosets are molded, it cannot be ground up and reprocessed or remolded.
Benefits of Thermoset Plastics
- Corrosion and Steam Resistant
- High Dielectric Strength
- Excellent Chemical and Dimensional Stability
- High Strength-to-Weight Ratio
- Excellent Thermal Properties
- Low Creep/Shrink
- Heat Resistant
- Superior Thermal Insulation
