Abstract
This study deals with the relation between weight changes and the bending properties of GFRP panels immersed in hot water. The GFRP panels used in this study were three kinds of randomly oriented E-glass fibre continuous strand mat reinforced unsaturated polyester resins. These panels were different in matrix resin and filler content. The water immersion tests were conducted at 80°C and the specimen weight before and after immersion was measured. After water immersion, three point bending tests were performed in order to evaluate the reduction in elastic modulus and strength. Weight changes were evaluated in two ways: the weight gain due to water absorption and the weight loss due to matrix dissolution. The water absorption kinetics was different from the typical Fickian diffusion behaviour, and a great amount of water penetration into the interface was associated with weight loss. Extensive weight loss due to matrix dissolution was caused by degradation at the fibre/matrix interface. The main causes of the modulus and strength reduction of GFRP immersed in water were clarified from the relation between weight changes and bending properties. The elastic modulus decreased with increasing water absorption, and eventually it became constant. The strength decreased linearly with the weight gain due to water absorption. The modulus and strength reductions were caused by the degradation of matrix resin due to water absorption-related processes, such as plasticisation and hydrolysis. However, the modulus reached a constant value in spite of a great amount of water absorption and this was caused by extensive degradation at the interface. The strength reduction observed along with matrix dissolution was caused by the reduction in the load bearing capacity of the fibre following interface breakdown.
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