Epoxies

Epoxies are a family of thermosetting polymers that contain epoxide functional groups. They are typically produced by reacting epichlorohydrin with bisphenol A to yield diglycidyl ethers (DGEBA) or by using other phenolic resins. The resin is then crosslinked (cured) with hardeners such as amines or anhydrides to produce a rigid, solvent-resistant network.

Curing and formulations: The curing agent, chosen based on required properties, determines cure temperature and rate. Common hardeners include amines (cycloaliphatic and polyamines), anhydrides, and phenolic or mercaptan catalysts. Curing can occur at room temperature for some systems or at elevated temperature for higher crosslink density. Additives such as flexibilizers, tougheners, fillers, and pigments tailor properties.

Properties: Epoxies exhibit strong adhesion to metals, glass, and composites, high stiffness and strength, good chemical and solvent resistance, and excellent electrical insulation. They can be formulated for rigid or tough, impact-resistant systems and for high-temperature performance. However, they may be brittle unless modified, and UV exposure can cause yellowing in certain formulations.

Applications: Used as coatings (protective and corrosion-resistant), structural and decorative adhesives, matrix resins for fiber-reinforced composites, encapsulants and potting compounds for electronics, gaskets and sealants, and casting resins.

Processing and safety: Handling requires PPE; epoxy resins and hardeners can cause skin sensitization and eye irritation. Exothermic curing can generate heat; proper ventilation and curing schedules are important. Storage stability varies; many epoxies are moisture sensitive.

Environmental and research notes: There is ongoing development of bio-based and low-VOC epoxies, and challenges include recyclability of thermosetting networks. The term epoxy resin loosely refers to both the resin and the cured polymer.