Bonding and fracture properties of SPI-CNTs/epoxy adhesive on SPI-CNTs deposited CFRP composites

Abstract

Adhesive bonding is frequently used to connect CFRP structures due to its lightweight, easy implementation and high production efficiency. However, the bonding performance of adhesive is far from satisfactory as dimension and complexity of CFRP structures increase. In this paper, a new bonding strategy for CFRP structures via introducing soy protein isolate modified carbon nanotubes (SPI-CNTs) both in the epoxy resin adhesive and on the bonding parts' surface is proposed. Results showed that SPI can effectively improve CNTs' dispersion on the two areas, notably enhancing the bonding performance of the adhesive. When 0.3 wt% SPI-CNTs was added in the adhesive, its adhesive shear strength increased to 12.76 MPa, which was 72 % higher than the unmodified CNTs/epoxy adhesive. Based on this concentration, the SPI-CNTs was deposited uniformly on the surface of the CFRP adherends via bath sonication and resulted in a maximum shear strength of 15.59 MPa, which was 22.2 % greater than the untreated ones. Based on the above condition, the Mode I fracture toughness G1c and the Mixed-Mode I/II fracture toughness Gc could reach a maximum of 0.31 and 0.44 N/mm respectively, which were 117 % and 97 % higher than the pure epoxy adhesive. The present work shows a new pathway for the effective bonding of CFRP structural components used in the aerospace industry.