Toughening Epoxy Adhesives to Meet Today’s Challenges

Abstract

There are many advantages that polymeric adhesives can offer compared with the more traditional methods of structural joining such as bolting, brazing, welding, and mechanical fastening, and epoxy adhesives represent the most common type of structural adhesive. When polymerized, epoxy adhesives are amorphous and highly cross-linked materials, and this microstructure results in many useful properties for structural engineering applications, such as a high modulus and failure strength, low creep, and, by careful formulation, good performance at elevated temperatures. However, the structure of such thermosetting adhesives also generally leads to one highly undesirable property: they are relatively brittle materials, with poor resistance to crack initiation and growth. Nevertheless, the incorporation of a second phase of dispersed rubbery particles into the epoxy polymer can greatly increase their toughness without significantly impairing their other desirable engineering properties. Thus, rubber-toughened epoxy adhesives can be used, for example, in applications where very high impact resistance is required for the bonded joint.