Fracture Toughness of Elastomer Modified Epoxy Adhesives

Elastomer modification is an effective way of toughening glassy epoxy resins. The toughening mechanisms of phase separation and gellation have been studied extensively. This paper reports the effects of carboxyl terminated acrylonitrile rubber on several single component epoxy adhesives, based on Epon 828 and cured with dicyandiamide. Variables include accelerator type and level, cure temperature and elastomer level. There is an optimum amount of rubber which may be added to each system to yield maximum shear strength. Peel strength is maximized in two regions. Rapid gellation of these adhesives may be detrimental to the phase separation and chain extension mechanism and thereby cause lowering of fracture toughness and strength properties.