Understanding the Chemistry Behind Epoxy

Epoxy is a versatile material used in a variety of applications, from adhesives to coatings. But what is it, and how does it work? Epoxy is a combination of two components: an epoxy resin and a hardener. When these two components are mixed together, they initiate a chemical reaction that transforms the liquid ingredients into a solid. This process is known as curing.

Epoxy resins are a broad class of prepolymers and polymers that contain more than one epoxy group, also often referred to as glycidyl or oxirane groups. These epoxide groups are responsible for the chemical reaction that occurs when the resin and hardener are mixed together. The IUPAC name for an epoxide group is oxirane. The curing process involves a polyaddition reaction that results in coupling and crosslinking.

This crosslinking is responsible for the stiffness and strength of epoxy materials. The chemical bond in the epoxy resin is firm, giving it the ability to stick until it dries completely. When dried in the open air, 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. The ability of this ring to react in a variety of ways and with a variety of reagents gives epoxy resins their great versatility.

The most commonly used curing agents are compounds containing active hydrogen (polyamines, polyacids, polymercaptans, polyphenols, etc.). The term epoxy can also be used to refer to epoxy resins that appear after curing. Approximately half of the production of epoxy resin is used for surface coating applications, and the rest is roughly divided equally between electronic applications (in particular for printed circuit boards and encapsulation), the construction industry and miscellaneous uses. Workers may be exposed to uncured epoxy resins if they are not adequately protected or are not handling epoxy resins with the right tools. Due to low dielectric constants and the absence of chlorine, cycloaliphatic epoxides are often used to encapsulate electronic systems, such as microchips or LEDs. Many properties of epoxies can be modified (for example, silver-filled epoxies with good electrical conductivity are available, although epoxies are typically electrically insulating).

An important criterion for epoxy resins is the epoxy value, which is related to the content of the epoxy group. Therefore, with a global consumption of approximately 10 million tons per year for thermosetting plastics, epoxy resins had a share of approximately 3%. The specific reactions of the various reagents with epoxide groups have often been studied in considerable detail and have been extensively reviewed elsewhere. The reaction of polyepoxides with themselves or with polyfunctional hardeners forms a thermosetting polymer, often with favorable mechanical properties and high thermal and chemical resistance. More viscous or thicker epoxies have added fillers such as copper, sand and talc, the main ingredient in baby powder. The secondary amine can further react with an epoxide to form a tertiary amine and an additional hydroxyl group. 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. Once in the solid state, it cannot be cured. Epoxies contribute to a variety of products and technologies that help improve energy efficiency and reduce greenhouse gas emissions.