Weight changes of the fibre/matrix interface in GRP panels immersed in hot water

Abstract

The weight-change behaviour of the fibre/matrix interface in composite panels consisting of randomly orientated E-glass-fibre continuous strand mat in unsaturated polyester has been studied. Two matrix resins of different filler content were used. GRP and plain resin specimens were immersed in hot water (60°C and 80°C) and the weight of the specimens was measured as a function of time. The weight changes were evaluated in terms of three parameters: apparent weight gain, net weight gain and weight loss. The weight changes of the fibre/matrix interface were obtained from the differences in the weight changes of the GRP and the unreinforced resin. Water absorption at the interface occurred after water absorption of the matrix resin reached almost saturation level. Weight loss due to dissolution of binder from the interface occurred after water penetration into the interface. Debonding occurred at the fibre/matrix interface as a result of water penetration, and, in consequence, the binder dissolved into water at the interface. The net weight gain and weight loss of the interface increased linearly with the square root of immersion time, and the filler had little effect on these phenomena.