Thermoset plastics are synthetic materials which undergo a chemical change during processing to strengthen and set them into a form. Examples of thermoset plastics include epoxy, silicone, amino, phenolic and unsaturated polyesters.
Thermoset plastics are contrasted by thermoplastics, which soften when heated and strengthen and set into form as they are cooled. Thermoset plastics have a net-like structure of cross-linked polymers. Once they have undergone the initial chemical change during processing, they cannot be melted or remolded. They are also resistant to solvents.
Because of these basic properties, thermoset plastics are inherently strong and durable even under high-heat conditions, although they are somewhat brittle. These plastics are often used to make large and/or permanent parts or shapes such as automobile bodies. They are also used in electronic chips, polymer coatings, the coatings on eyeglasses and in dental fillings. Vulcanized rubber is another example of a thermoset plastic material.
Thermoset plastics are typically produced by heating a powder or liquid in a mold. The chemical change that sets the thermoset plastics may or may not have to do with the application of heat. In some cases, it is the result of the chemical interactions of the components. Each type of thermoset plastic has its own set of unique properties.