Due to excellent heat and corrosion resistant properties, thermosets are used in a variety of end-markets and applications. Many engineers and designers look to implement thermoset plastics into a challenging product design due to thermosets’ excellent dimensional and chemical stability when exposed to heat and high operating temperatures.
Similar to thermoplastic molding, thermosets may be injection, compression, injection-compression, and insert molded. The difference is that thermosets strengthen when heated, and 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 thermosets, engineered thermoplastics will soften or disfigure when re-heated after molding, jeopardizing the dimensional and chemical integrity 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 or baking a cake. Once it is cooked, reheating does not cause melting or disfiguration, so it cannot be remolded.