Study on the effect of surface morphology on adhesion properties of polybenzimidazole adhesive bonded composite joints

Surface wetting properties of polymer based composite materials play a crucial role in the achievement of better adhesive bonding. In the present work, efforts are made to evaluate the effect of surface morphology on adhesion properties of two different epoxy based carbon fiber composite materials before and after performing the atmospheric pressure plasma treatment and hand sanding. In this study, high performance thermoplastic polybenzimidazole (PBI) adhesive having a glass transition of 425 °C is used as an adhesive. PBI adhesive bonded joints were formed using M21 epoxy based and DT120 epoxy based carbon fiber composites. Experimental results demonstrate that surface morphology plays a very critical role in achieving a high lap shear strength. Due to better surface morphology, DT120/carbon composite bonded joints exhibits four times higher lap shear strength even without performing any surface treatment. Furthermore, plasma treated composite bonded joints have shown higher lap shear strength when compared to the hand sanded composite bonded joints. Lap shear strength of bonded joints is correlated with surface morphology of plasma treated and hand sanded samples. SEM analysis of treated surfaces demonstrates that plasma treatment has changed the surface morphology without damaging fibers on the surface; whereas hand sanding treatment has damaged some fibers on the surface which ultimately leads towards a weak substrate/adhesive interface and hence resulted in lower bonded joint strength.