Synergetic Improvement of Interlaminar Fracture Toughness in Carbon Fiber/Epoxy Composites Interleaved with PES/PEK-C Hybrid Nanofiber Veils

In this study, two types of soluble thermoplastic resins were added to epoxy resin at a fixed weight ratio to prepare a three-phase cast body. The cast was then manufactured into hybrid nanofiber as interleaves for interlaminar toughening of carbon fiber/epoxy resin (CF/EP) composites using a co-solvent method. The results revealed that when the hybrid components reached 15 wt%, Polyethersulfone (PES) and polyaryletherketone cardo (PEK-C) exhibited the best synergistic toughening effect, and the fracture toughness increased by 99.8% and 39.8%, respectively, compared with the reference or the same proportion of the single PES toughened sample. We used PES/PEK-C hybrid nanofibers with an areal density of 19.2 g per square meter (gsm) as composite toughening layers. Apart from the lack of significant influence of PES nanofiber on CF/EP composites, the interlaminar fracture toughness of mode I and mode II layers increased by 88.3% and 46.9%, respectively, compared to the reference sample. Scanning Electron Microscopy of the fracture surface and cross-section micromorphology of the laminate displayed that the thermoplastic microspheres of different sizes contribute differently to crack resistance: PEK-C consumes more energy due to the debonding and extraction of microspheres and resin, whereas the presence of the PES phase can induce more plastic deformation and crack deflection.