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The Chemical Composition of Epoxy
Epoxy is a thermosetting epoxide polymer. Thermosetting means that epoxy is an adhesive that cures and cannot be uncured. An epoxide is simply a chemical that is more reactive to other chemicals; however, a polyepoxide, such as epoxy, is comprised of unreacted epoxide. This means that pure epoxy is very susceptible to reaction with other chemicals. The other chemical in the case of epoxy is a hardening or curing agent, which reacts with the polyepoxide to cure into a very strong adhesive.
The Process from Liquid to Solid Adhesive
To apply an epoxy, one must mix together two chemicals, the polyepoxide and the hardening agent. When mixed together, the polyepoxide reacts with the hardening agent. This means that the chemical bonds in the mixture actually change. In this case, the monomers comprising the polyepoxide bond in a network of ether. That is chemistry jargon for molecules becoming a considerable amount stiffer. By using different hardening agents that react slower or faster to the polyepoxide, epoxy producers can change the duration of the curing period for the epoxy.
The End Result
After curing, the epoxy becomes a very strong adhesive that is resistant to other chemicals and weathering. The reason it is such a great adhesive is that when applied between two things, it seeps into the pores of the two objects meant to be joined together. The epoxy, once it has seeped in the pores of the two objects, hardens and creates solid, epoxy links between the two objects, making them extremely difficult to separate.