Effect of surface treatments on the durability of green polyurethane adhesive bonded aluminium alloy

Surface treatment of aluminium alloy plays a significant role in improving the strength of the adhesive bond. In this study, an aluminium alloy 2024-T3 was treated by two different methods of surface treatments i.e. by alkaline etching and warm water treatment followed by silanization method in order to enhance the adhesive bonding. Three different formulations of polyurethane adhesive by varying the NCO:OH ratios which were prepared from polyol polycaprolactone (PCL) based on palm kernel oil polyesteramide (PPKO) with a blend of aromatic and cycloaliphatic diisocyanate. Surface morphology, surface chemical analysis, wettability and surface roughness of the treated samples were characterised using field emission scanning electron microscopy and energy dispersive X-ray analysis (FESEM/EDX), X-Ray Photoelectron Spectroscopy (XPS), contact angle goniometry and surface profilometry, respectively. The influences of surface treatment techniques and conditions on durability of the joint strength and interfacial properties were explored by performing the single lap shear test and wedge test. The effects of NCO:OH ratios on PU adhesive strength were also investigated. Durability of PU adhesive bonding is found to display an interesting dependence on the surface treatments.