Synergetic effects of carbon nanotubes and triblock copolymer on the lap shear strength of epoxy adhesive joints

Abstract

This paper investigated the effect of functionalized CNTs and triblock copolymer addition on the lap shear strength of the epoxy adhesive joints. CNTs were functionalized using an ultrasonicated-ozonolysis process to enhance the uniform and stable dispersion of CNT, and 3-roll mill was employed to achieve the uniform distribution of CNT in the epoxy matrix. Two different triblock copolymers named as SBM and MAM were used as toughening agents to improve the shear strength of the nanocomposite adhesive material. Single lap shear tests were performed on the aluminum adhesively bonded joints using pure and modified epoxy adhesives to determine the shear strength of the adhesive. The effect of different weight fractions of untreated CNTs, functionalized CNTs, and the hybrid effect of CNTs and triblock copolymer addition on the shear strength of the adhesive joints was studied. It was found that the use of functionalization and 3-roll mill methods are effective to achieve stable and even dispersion of the CNTs and the shear strength was improved by 26% (23.6 MPa) compared to that of pure epoxy. The hybrid effect of functionalized CNTs and SBM showed the maximum shear strength of 44.7 MPa, with an increase of 137% compared to that the of the pure epoxy demonstrating the effectiveness of the triblock copolymer addition in improving the shear strength. Fracture analysis revealed that the nano-additives acted synergistically to increase fracture ductility which contributed to increase the shear strength. In addition, glass transition temperature and thermal stability of the modified epoxy were found to be relatively unaffected.