Improvement of interlaminar fracture toughness in carbon fiber/epoxy composites with carbon nanotubes/polysulfone interleaves

Carbon fiber/epoxy (CF/EP) composites have been widely used as structural materials in many aerospace applications owing to their superior specific strength and specific elastic modulus. However, interlaminar delamination, the most common failure mode of these composite materials, often occurs due to the inherent brittleness of the epoxy matrix. In this study, a vacuum filtration method was used to fabricate sandwiched carbon nanotubes/polysulfone nanofiber (CNTs/PSF) paper as an interleaf to improve the interlaminar fracture toughness of CF/EP composite laminates. During curing of the epoxy resin, the PSF nanofibers were first dissolved and then phase separated from the continuous epoxy matrix to form microspheres while the CNTs were dispersed homogeneously in the epoxy. It was found that interleaving the laminates with the sandwiched paper increased both mode I and mode II interlaminar toughness. Also, the CNTs/PSF interleaved laminates displayed an increase in flexural strength and flexural modulus owing to the reinforcing effect of the CNTs. DMA tests confirmed that better compatibility between PSF and epoxy could be achieved by adding CNTs. The mechanisms for the simultaneous improvements of toughness and flexural properties were analysed.