Adhesion of epoxy resins to metals

Abstract

The adhesion of an epoxy resin above its glass transition temperature to aluminium, steel and gold surfaces has been studied using the methods of fracture mechanics. The results are compared with those of a previous study of elastomeric adhesives by Andrews and Kinloch, and the “intrinsic failure energies”,θ ₀, for the epoxy-metal bonds are deduced by similar methods. Correspondence, within a factor of two, is found betweenθ ₀ and the thermodynamic work of adhesion,W _A, for most cases of interfacial failure, indicating both the absence of specific or chemical interactions at the interface and a purging of surface contaminants by the epoxy. An exception occurs when an excess of epoxy groups exist in the uncured resin. Here, for steel and aluminium but not for gold, the interfacial bonding is stronger than the cohesive strength of the resin due probably to the formation of strong bonds with the metal oxide surface layer.