What Plastics are Thermoset?

Thermosets are a niche grade of plastic or composite molding materials compared to common engineered thermoplastics such as PA66 (nylons), ABS, Polypropylene, etc. While thermosets are much less known, they have been used in various components longer than thermoplastics. The original plastic material, bakelite, created by Leo Baekeland in 1907 was a type of thermoset composite. Although thermoset materials have been molded and used in components dating back a century ago, thermosets are now used commonly towards specialty end use applications that experience high heat or electrical current. Where a thermoplastic molded part may degrade and disfigure under such elements, thermosets remain durable and strong due to the high temperature resistance and dielectric strength.

Common thermosets molded in the market today include phenolic molding compound, bulk molding compound (BMC) which can be an unsaturated polyester and vinylester, epoxy, and diallyl phthalate (DAP), and sheet molding compound (SMC) which is similar to a BMC, but may offer higher strength properties and is traditionally compression molded. These thermoset materials are processed via injection, compression, injection-compression hybrid, transfer, and insert molding processes. Each thermoset material has various advantages over the other types of thermoset materials, however in general, most all thermosets offer superior heat and chemical resistance compared to engineered thermoplastics. While Phenolic, DAP, and some Epoxies are all compounded into a similar state to thermoplastics as granular form, BMC is extruded into a playdough like form that requires a stuffer system to inject material from the molding machine into the mold for injection molding processes.