Carbon nanotube reinforced epoxy based adhesive: Correlations between chemical functional and failure modes

Abstract

This paper addresses correlational studies among failure mode analysis, fracture morphology, and the chemical changes for a single-lap bonded joint (SLJ) based on an industrial adhesive. The SLJ bonded joint was selected due to its stress combination inside the adhesive, i.e., peel and shear. The increase in the Fourier-transform Infrared (FTIR) intensity of chemical functional, i.e., rocking of CH2 group, C–O–C stretching of oxirane group, C–C stretching vibration, C=C aromatic ring stretching, are related to the ductile-like fracture morphology due to more molecular mobility. At meanwhile, the increase in intensity of asymmetrical vibration CH2 and O–H stretching vibrations are related to brittle-like morphology fracture. The cohesive failure is related to the ductile-like failure morphology, while the adhesive failure is linked to brittle-like morphology fracture. At room temperature, then best option is the 0.25 wt % carbon nanotubes (CNT), as cohesive failure modes are prevalent. The addition of carbon nanotubes to the industrial adhesive reduces the high temperature environmental degradation. However, the addition of carbon nanotubes had small influence into glass transition temperature variations. Considering the amount of CNT dispersed into the epoxy system, and the 100 °C long time exposures, it seems that the 1.0 wt % CNT content is the best option. The reasons for such differences are due to changes at chemical functional caused by the prolonged exposure to temperature higher than the glass transition temperature. Such changes were identified by the FTIR spectroscopy analysis.