Thermoset plastics, or thermoset composites, are synthetic materials that strengthen when heated, but cannot successfully be remolded or reheated after initial heat-forming. Post mold, thermoset composites are resistant to high operating temperatures, corrosion, and chemicals. Molded thermoset parts will not disfigure or degrade chemically or dimensionally when exposed to heat or fluids. In contrast to thermosets, thermoplastics such as Nylon, ABS, PP, or PET will soften or disfigure when re-heated after molding, jeopardizing the integrity of a molded component.
Common thermoset materials used within thermoset injection molding applications are Bulk Molding Compound (BMC) or Dough Molding Compound (DMC), which are saturated and unsaturated polyesters and vinyl esters; Phenolic Molding Compound, Epoxy, and Diallyl Phthalate (DAP). Most commonly, Woodland Plastics injection molds BMCs and Phenolics.
Understanding Thermoset Plastics
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. 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 an egg has been cooked, reheating does not cause melting or disfiguration, and the cooked egg cannot revert to its original physical state as a yoke. Once a thermoset is cured, the material or molded part cannot be grinded and reprocessed or remolded.