Interfacial properties and water resistance of epoxy and CNT-epoxy adhesives on GFRP composites

Epoxy adhesives have been widely used to bond two different structural materials tightly together. Durability and strength of adhesion under aqueous and humidity circumstance have recently been deemed of particular importance for adhesives. This paper reports on studies of and the comparison of mechanical properties and interfacial durability in air as well as under moist conditions, or under water, of conventional bisphenol-A type epoxy and carbon nano tube (CNT) added epoxy adhesives. These studies included measurements of static contact angle, surface energy, and work of adhesion between CFRP laminate and CNT-epoxy adhesives to verify durability of the interfacial adhesion. Epoxy and CNT-epoxy adhesives were cured under aqueous condition and water penetration for comparatively evaluation. Cyclic lap shear tests were also used to evaluate the durability of lap shear strength of both epoxy and CNT-epoxy adhesives. The CNT-epoxy adhesive exhibited a significant retention in shear strength under moist conditions. During fracture the adhesives were evaluated using acoustic emission (AE) of the neat and CNT-epoxy adhesives in air and in aqueous conditions. Mechanical and interfacial properties of the CNT-epoxy adhesive were better than those of the neat epoxy adhesive, especially water resistance.