Ozone functionalized graphene nanoplatelets and triblock copolymer hybrids as nanoscale modifiers to enhance the mechanical performance of epoxy adhesives

In the present work, the mechanical and fracture performance of a newly developed high-performance nanocomposite adhesive was characterized experimentally. The nanocomposite adhesive was based on an epoxy resin, which was modified with 10 wt% of triblock copolymers (BCPs) including styrene-butadiene-methylmethacrylate (SBM) and methylmethacrylate-butylacrylate-methylmethacrylate (MAM), and ozone-functionalized graphene nanoplatelets (OZ-GNPs). The mechanical properties of the adhesive joints were systematically evaluated using lap shear, tensile-butt, and Mode-I fracture toughness tests. The lap shear strength and the ultimate shear strain of the 1.0 wt% OZ-GNP + SBM ternary nanocomposite epoxy adhesives obtained 91% and 97%, while 1.0 wt% OZ-GNP + MAM adhesives attained 64% and 63% improvement, respectively, compared to that of the pure epoxy. Consequently, the potential load capacity was improved by about 93% (1.0 wt% OZ-GNP + SBM) and 62% (1.0 wt% OZ-GNP + MAM) compared to that of pure epoxy joints. However, the tensile butt joint strength of the nanocomposite adhesives was slightly reduced due to the lower stiffness of the BCPs. The mode-I fracture toughness results for the 1.0 wt% OZ-GNP + SBM and 1.0 wt% OZ-GNP + MAM increased significantly by approximately 1000% and 200%, respectively, compared to the unmodified epoxy adhesive. Fractography using scanning electron microscopy showed the formation of BCP nanostructures, plastic deformation, crack deflection, debonding of the BCP, and subsequent plastic void growth, which all contributed to the increase in the fracture toughness of the nanocomposite adhesives. The extent of the plastic deformation zone was enhanced by the addition of OZ-GNPs.