Carbon nanotubes and core–shell rubber nanoparticles modified structural epoxy adhesives

In this study, multi-walled carbon nanotubes (MWCNTs) and core–shell rubber (CSR) nanoparticles were dispersed in an epoxy adhesive to produce conductive and tough structural adhesives. The thermo-mechanical properties, electrical conductivity, fracture toughness and lap shear strength of MWCNT–CSR–epoxy structural adhesives were studied. The addition of both MWCNTs and CSR nanoparticles into the epoxy adhesive increased the fracture energy significantly, from 397 J/m2 for the unmodified adhesive, to 2615 J/m2, for an adhesive modified with 10 wt% CSR nanoparticles and 0.3 wt% MWCNTs. The toughening mechanisms of the CSR nanoparticles were identified as cavitation of the rubber particles followed by plastic void growth and shear band yielding. The toughening enhancement of the MWCNTs was mainly attributed to the crack bridging, MWCNT break and crack path deflection. The addition of CSR nanoparticles into neat epoxy was found to affect the failure mode of the lap shear joints, from brittle, interfacial failure, to a ductile, cohesive failure. A moderate increase in the strength of the lap shear joint was also noted. The subsequent addition of MWCNTs further affected the failure mode of the lap shear joints. A mixture of interfacial and cohesive failure was observed for each joint configuration. The lap shear strength was observed to have increased significantly, by 39%, due to the addition of 0.5 wt% MWCNTs. The observed increase in lap shear strength with the addition of MWCNTs was attributed to the crack deflection caused by the MWCNTs.