Toughening of a carbon fibre reinforced epoxy anhydride composite using an epoxy terminated hyperbranched modifier

An epoxy terminated hyperbranched polymer (HBP) has been used to toughen a carbon fibre reinforced epoxy anhydride composite. This report describes the changes in viscoelastic properties used to measure the effect of HBP upon the reaction kinetics, viscosity and phase separation process occurring during cure. An appropriate cure profile was determined to ensure an optimum morphology development during fabrication of the composite containing varying amounts of HBP. The increases in the mode I and II interlaminar fracture toughness of the composite material were found to be 224% and 265%, respectively, at a loading of 10 wt% of HBP additive. Other properties such as interlaminar shear strength, flexural modulus and strength were found to decrease modestly while the glass transition, thermal stability (measured via thermogravimetric analysis) and the transverse coefficient of thermal expansion were largely unaffected. The substantial increase in toughness was attributed to the high level of interaction between the HBP and epoxy anhydride matrix measured from the varying positions of the β relaxation peaks using dynamic mechanical thermal analysis.