Thermoset plastics are used in a variety of markets and applications. Generally, there is one common variable for these applications – heat. Many Engineers and Designers look to implement thermoset materials into their product designs due to thermosets’ high heat deflection and heat resistance. As a heat resistant plastic, thermoset materials provide excellent dimensional and chemical stability when exposed to high heat.
Similar to thermoplastics, thermosets may be compression, compression-injection, and injection molded. The difference is that thermoset, or thermosetting plastics, strengthen when heated, yet cannot be successfully remolded or reheated post-mold. After initial heat-forming, the properties of thermoset plastics become “set”, and components are resistant to heat, corrosion, and creep. In contrast to thermoset plastics, engineered thermoplastics will soften or disfigure when re-heated, jeopardizing the dimensional and chemical stability of a component.
While a thermoplastic monomer has only two reactive ends for linear chain growth, a thermoset monomer must have three or more reactive ends, with its molecular chains crosslinking in three dimensions. Post-mold, thermosets have virtually all molecules interconnected with strong, permanent, physical bonds, which are not heat reversible.
Theoretically, the entire molded thermoset part can be a giant, single molecule. In a sense, curing a thermoset is like cooking an egg. Once it is cooked, reheating does not cause melting or disfiguration, so it cannot be remolded.