Phase morphology and fracture behaviour of CNT and thermoplastic modified epoxy ternary nanocomposite by different processing methods

Abstract

CNT modified thermoplastic toughened epoxy nanocomposites used as potential matrix materials for fibre reinforced composites were prepared and compared. During the preparation step, CNTs were added, in two different ways to investigate the consequences of changing the order of addition in the final properties of the nanocomposites. It was shown that the presence of CNTs has a great impact on different aspects of the phase separation process of the thermoplastic particles and the resulting phase morphologies. Nanotubes in ternary blends with CNTs initially added to the epoxy phase showed a better dispersion in comparison with the other type where CNTs were initially added to the thermoplastic phase. The difference in morphology and microstructure of the blends including nanotubes with those without CNTs were attributed to the increase in the local viscosity, limiting the mobility and hence the growth of the thermoplastic phase following phase separation. This resulted in the formation of smaller particles with a wider distribution in particle size. Mode-I fracture toughness of the ternary blends with CNTs initially added to the epoxy phase, showed a synergistic increase where the gain in fracture toughness was higher than the combined increases resulted from addition of the thermoplastic and nanotubes individually. A more uniform distribution of carbon nanotubes in this system made it possible for the thermoplastic microparticles to exhibit a plastic deformation during crack propagation, as evident from the micrographs of the fracture surfaces. This together with the formation of shear bands in the epoxy matrix and the pull-out of the nanotubes were identified as the most important energy dissipation mechanisms, largely contributing into the observed synergistic increase in the fracture toughness.