Effect of carbon nano-filler addition on the degradation of epoxy adhesive joints subjected to hygrothermal aging

In this study, the effect of hygrothermal aging on the strength of pure and carbon nano-filler reinforced epoxy adhesive joints is presented. Epoxy adhesives containing three different carbon nano-fillers, namely, multi-walled carbon nanotubes (CNT), graphene nanoplatelets (GNP) and single walled carbon nanohorns (CNH) were prepared by using a high shear rate mixer. Thermogravimetric analysis (TGA) of the nano-filler reinforced epoxy indicated an improvement in the thermal stability compared to pure epoxy. Aging studies were carried out on single lap-shear specimens as per EN ISO 9142:2003 standard (cycle D3). The strength of the joints was found to decrease with hygrothermal aging time. The nano-filler reinforced joints showed less reduction in joint strength with aging compared to pure epoxy joints. The GNP/epoxy joints showed the best resistance to aging followed by CNT and CNH reinforced joints. Fourier Attenuated Total Reflectance Transformation Infrared Spectroscopy (ATR-FTIR) analysis of the hygrothermal aged samples indicated lower degradation in terms of hydrolysis of epoxy groups for nano-filler reinforced epoxy. Gravimetric analysis of samples immersed in water showed lower weight gain for nano-filler reinforced epoxy composites. Fracture surface analysis was carried out to study the change in failure mechanism with aging time.