Effect of carbon black nanoparticles concentration on the mechanical properties of a structural epoxy adhesive

The present work describes the influence of different carbon black nanoparticles with different concentrations on the mechanical properties of a structural epoxy adhesive cured by dielectric and thermal heating. This work was undertaken to improve the understanding of the effect of carbon black nanoparticles concentration on the stiffness (Young's modulus), strength (yield strength) and deformation of the adhesive. Two kinds of spherical carbon black nanoparticles with different dielectric properties and sizes were used. Specimens with different amounts of carbon black were manufactured for each nanoparticle. The mechanical properties of the adhesive were measured in bulk specimens. The mechanical properties were found to vary as a function of the carbon black amount. For the dielectric cure, the strength and stiffness of the adhesive decrease as the amount of carbon black nanoparticles increases. On the other hand, the adhesive showed an increase of the deformation with an increase of the carbon black concentration. The thermal cure showed a mechanical behaviour similar as the dielectric cure, but the curing time increases substantially. A scanning electron microscopy analysis was performed to analyse the surface fracture of the adhesive. The fracture surfaces of specimens cured by dielectric and thermal heating and without nanoparticles are similar, typical of brittle adhesive. For high carbon black amount, the fracture surfaces are typical of ductile adhesive.