Interlaminar fracture toughness improvement in composites with hyperbranched polymer modified resin

The present work aims to enhance the interlaminar toughness of carbon/epoxy composites produced by RTM by modifying the resin with hyperbranched polymers (HBPs). A HBP content of 7.5% in the resin was selected as the best compromise between a slight loss in stiffness and a gain of 60% in fracture toughness. Composites manufactured with the modified resin did not show such improvement in terms of interlaminar shear strength when double cantilever beam (DCB) specimens were subjected to crack opening. In the case of composites made of pure epoxy, a value of GIC = 600 J/m2 was found, whereas for the modified resin based composite, GIC was equal to 750 J/m2. Fibre pullout tests indicated that adhesion at the fibre-matrix interface was poor in case of the modified epoxy. Adding amine to the modified resin was shown to counterbalance this depreciation, raising GIC of the composite to 1400 J/m2.