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

• Carbon fibre/polybenzoxazine composite laminates were produced with and without polyethersulfone particles in the interlaminar region using vacuum assisted resin infusion
• Polyethersulfone particles formed a strong interphase with the matrix in the interlaminar region enhancing the mode-I fracture toughness
• Mode I interlaminar fracture toughness for initiation and propagation increased by 110% and 139% respectively with a higher molecular weight polyethersulfone compared to the reference
• Mode I interlaminar fracture toughness for initiation and propagation increased by 73% and 56% respectively with a lower molecular weight polyethersulfone compared to the reference
• Addition of the polyethersulfone particles decreased the onset of the storage modulus, but increased the glass transition temperature

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.

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