Toughening of epoxy resins

Epoxy resins constitute an important class of thermosets which are used extensively in the field of composites, adhesives surface coatings, etc. They are of aliphatic, cycloaliphatic or aromatic backbones. Epoxy resins based on bisphenol A are commercially available and they have good thermal and mechanical properties. They are cured by a variety of curatives, such as amines and anhydrides, and the mechanism of curing largely depends on the type of curing agent used. They show comparatively low cure shrinkage. Cured epoxies are brittle with poor resistance to crack initiation and growth. Their mechanical properties, in particular toughness, can be modified by incorporating a rubbery phase into the resin matrix. The epoxy matrix can also be modified by various other methods such as incorporation of thermoplastics and particulate fillers. The toughening process leads to improvement in fracture toughness and impact resistance. This review examines the various options and the state-of-the-art vis-a-vis epoxy modification.