The deleterious effect of cyclic hygrothermal aging on nanocomposite adhesives

The vulnerability of epoxy-based adhesives and resins to hygrothermal conditions limits their applicability in aggressive environments. Adhesives and resins are often exposed to repeated environmental conditions. In this paper, the effect of hydrophilic and hydrophobic nanofillers on the residual water, the coefficient of water diffusion, the strength and stiffness of nanocomposite adhesives under water absorption, desorption and resorption was experimentally studied. The results showed that by drying the wet samples, water was partially desorbed and a part of the degraded strength was recovered. Then, re-wetting the specimens resulted in further water absorption and material degradation at a much higher rate. The nanocomposites were made of epoxy resin, Fe2O3 nanoparticles and graphene oxide nanoplatelets (GONPs). The nanofillers decreased the water uptake after wetting, while increased the residual water after drying by confining water movement inside the material. Moreover, Fe2O3 nanoparticles and GONPs improved the fracture strength after water absorption by 28.8% and 22.3%, after water desorption by 54.4% and 42.2% and after water resorption by 40.2% and 29.3%, respectively. Furthermore, Fe2O3 nanoparticles and GONPs improved the strength recovery by 39.9% and 29.1%, respectively, compared to the neat epoxy.