Toughening Epoxy Adhesives to Meet Today’s Challenges

There are many advantages that polymeric adhesives can offer compared to the more traditional methods of joining such as bolting, brazing, welding, mechanical fasteners, etc. and epoxy adhesives represent the most common type of structural adhesive. When polymerised, epoxy adhesives are amorphous and highly-crosslinked 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 in that they are relatively brittle materials, with a 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 the other desirable engineering properties. Thus, such rubber-toughened epoxy adhesives can be used, for example, in applications where a very high impact resistance is required for the adhesivelybonded joint.