Toughening of carbon fibre/polybenzoxazine composites by incorporating polyethersulfone into the interlaminar region

Two grades of hydroxyl-terminated polyethersulfone (PES), one low and one high molecular weight, were incorporated into carbon fibre/polybenzoxazine (CF/PolyBZ) composites as interlayer toughening agents. A preliminary study on the PES–benzoxazine (BZ) resin mixtures was carried out via hot stage microscopy to observe the dissolution behaviour of the PES in the BZ during the curing cycle. CF/PolyBZ composites with PES in the interlaminar regions were produced by a vacuum resin infusion process and characterised via double cantilever beam (DCB) tests to determine the mode-I type interlaminar fracture toughness (GIC). The DCB fracture surfaces were examined under an optical microscope and scanning electron microscope (SEM). The thermomechanical properties of the composites were also studied via dynamic mechanical analysis (DMA). The incorporation of both grades of PES resulted in a significantly improved GIC and marginally increased glass transition temperature of the composite. Keywords: Carbon fibres, Fracture toughness, Dynamic mechanical thermal analysis (DMTA), Scanning electron microscopy (SEM), Benzoxazine resin