Thermoplastics are materials that take a hardened form after they are heated and allowed to cool. When these materials are heated again, they generally convert to liquid and can be reformed. Thermosets also take a hardened form after they have been heated and allowed to cool. A major difference is that thermosets cannot be melted down and reformed. There are many types of thermosets, such as vulcanized rubber and epoxy resin.
Some materials, such as thermoplastics, can be found in forms that can be changed with heat. A simplified way of drawing a contrast is to view those items as many molecules that have been melted together but whose bonds can be released upon reheating. With thermosets, however, when the materials are heated, the molecules merge irreversibly. Reheating will not release the bonds. Instead, reheating is most likely to destroy the materials.
For this reason, thermoset materials are typically considered to be non-recyclables. For many people, this is a major disadvantage. There are many factors about thermosets, however, that can be seen as advantages. This includes their strength and durability.
Before thermosets are made, the materials are often in liquid form or another form that makes them susceptible to shaping. The process that those materials are put through to create the finished form is known as curing. There are several types of curing processes. Each tends to produce different types of materials.
One curing process is vulcanization, which is used to make vulcanized rubber for products such as tires, bowling balls, and hoses. There are several methods of vulcanization, but overall they are all generally considered irreversible processes. The rubber produced tends to differ from natural rubber in several ways. It is less sticky, resistant to heat, and more capable of holding the desired shape.
Some thermosets are produced when an epoxide, such as epichlorohydrin, is mixed with a hardener, such as bisphenol-A. Completion of such a polymerization process can result in epoxy resins. These materials are considered very versatile because most of their characteristics can be altered by making modifications during the process. Epoxy resins tend to have excellent chemical and heat resistance.
Epoxy resins are used in numerous industries. Artists use the material as a painting medium. In the electronics field, epoxy resin is used to produce circuit boards and transistors. It is also used by many as an adhesive.