Mechanical performance of adhesive joints using high-performance nanocomposite adhesive material with carbon nanotube and triblock copolymer hybrids

Abstract

This research investigates the mechanical performance of adhesive joints using high-performance epoxy (EP) based nanocomposite adhesive materials modified by ozone functionalized carbon nanotubes (OZ-CNTs) and two types of triblock copolymers (BCPs) including Methylmethacrylate-Butylacrylate-Methylmethacrylate (MAM) and Styrene-Butadiene-Methylmethacrylate (SBM). Different mechanical tests such as double-lap shear, tensile-butt, and Mode I long-crack extension tests were conducted to evaluate the effect of the BCP and OZ-CNT modification on the mechanical performance of the epoxy adhesive material. From the double-lap shear test, the strength of the 0.5 wt% OZ-CNT + SBM hybrid epoxy adhesive joint achieved a 112% increase compared to that of the unmodified epoxy. The ultimate plastic shear strain of the modified adhesives was significantly increased by 100% for the 0.5 wt% OZ-CNT + SBM/EP, representing a significant improvement in strain energy density and superior resistance to failure for any joints that would be applied in practice. However, the tensile-butt joint strength of the BCP/EP and OZ-CNT + BCP/EP joints was slightly lower than that of the unmodified epoxy, which was due to the presence of the lower strength and stiffness nanophase BCPs. The long-crack extension studies revealed a very large increase of Mode I fracture toughness of 1190% for the nano-modified hybrid joints with 0.5 wt% OZ-CNT + SBM/EP, showing that the OZ-CNT addition greatly enhances the fracture toughening processes provided by the SBM. It was also found that the addition of OZ-CNTs increased the electrical conductivity by 4 orders of magnitude compared with the unmodified and BCP modified epoxy. Rheological studies were also carried out to study the change in viscosity of the epoxy with the addition of BCPs and OZ-CNTs. The viscosity of the epoxy was increased with the addition of BCP or OZ-CNTs and the viscoplastic behaviour was observed for the hybrid OZ-CNT and BCP/EP adhesives, which was analysed using Casson's model.