What is Epoxy and How Does it Work?

Epoxy is a type of adhesive that is made up of a mixture of epoxy resin and hardener. When combined, these two components initiate a chemical reaction that transforms the liquid ingredients into a solid. This chemical bond is strong, giving it the ability to stick until it dries completely. When dried in the open air, the chemicals stick together to form a solid, shiny layer.

However, when placed between two materials, such as wood or fiberglass, the chemicals bond to adhere to the pores of the materials and solidify into place. This is why epoxy resin is practically impossible to remove when used as an adhesive. The term epoxy can also be used to refer to epoxy resins that appear after curing. Curing is a chemical process in which a material hardens after exposure to air, heat or chemical additives. In epoxy, curing occurs with the help of a catalyst, which is a chemical additive that increases the speed of a chemical reaction.

This results in an exothermic reaction that creates cross-linking in the polymer. This cross-linking is responsible for the stiffness and strength of epoxy materials. Epoxy is the family of basic components or cured end products of epoxy resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymer and polymers containing epoxide groups. The epoxide functional group is also collectively referred to as epoxy.

The IUPAC name for an epoxide group is oxirane. By mixing the epoxy resin with the hardener, a chemical reaction is initiated that transforms the combined liquid ingredients into a solid. As it cures, the epoxy changes from a liquid state to a gel state and eventually reaches a solid state. Once in the solid state, it cannot be cured. The excellent adhesive properties of epoxy resins are due to the attractive forces between the epoxy resin and the substrate surface.

These forces are usually polar forces or direct bonds that can form between the reactive sites on the resin and the reactive or polar sites on the surface of the substrate. Typical epoxy resins have pendant hydroxyl (-OH) groups along their chain that can form bonds or strong polar attractions to oxide or hydroxyl surfaces. They have polarity so that they have a high surface energy. Organic polymer surfaces are generally less polar (more covalent), so they have a lower surface energy. The condensation of epoxides and amines was first reported and patented by Paul Schlack of Germany in 1934. It can be used to describe the epoxide functional group, which is formed by a chain of carbon and oxygen atoms. Cycloaliphatic epoxides contain one or more aliphatic rings in the molecule in which the oxirane ring is contained (e.g., In this two-step reaction, epichlorohydrin is first added to bisphenol A (bis (3-chloro-2-hydroxypropoxy), bisphenol A is formed), then a bisepoxide is formed in a condensation reaction with a stoichiometric amount of sodium hydroxide.


are sold in hardware stores, usually as a package containing separate resin and hardener, which must be mixed immediately before use. Epoxies were modified in various ways, reacted with fatty acids derived from oils to produce epoxy esters, which were cured in the same manner as alkyds. Glycidylamine epoxy resins are higher functional epoxies that are formed when aromatic amines are reacted with epichlorohydrin.

An interesting point to make with epoxides is that woodworkers often like to darken their epoxy with a dye. The secondary amine can further react with an epoxide to form a tertiary amine and an additional hydroxyl group. An important criterion for epoxy resins is the epoxy value, which is related to the content of the epoxy group. Repairing a thin crack can benefit from a thinner formulation, while larger repairs need thicker epoxies. Also known as mercaptans, thiols contain a sulfur that reacts very easily with the epoxide group, even at room temperature or below room temperature. More viscous or thicker epoxies have added fillers such as copper, sand and talc, the main ingredient in baby powder. Because aliphatic epoxies have a lower electron density than aromatics, cycloaliphatic epoxies react less easily with nucleophiles than epoxy resins based on bisphenol A (which have aromatic ether groups).