Physical and water aging of glass fiber-reinforced plastic pipes

Physical and water aging of glass/epoxy composite - GFRE - pipes used for oil transport were investigated with special emphasis on their effect on the flexural and impact behavior. Different aging conditions were selected in order to simulate in-service environments trying to obtain reliable results from accelerated laboratory tests. In water uptake experiments at 80 degrees C, the mass increases continuously, suggesting that an irreversible process occurs. In addition, samples aged in air at 80 degrees C exhibit a DSC endothermic peak that can be related to physical aging. The calorimetric curve for specimens water aged at 80 degrees C shows combined effects of water absorption and physical aging. On the other hand, while the independent effect of temperature and water aging on the composites mechanical response is only moderate, their combined effect seems to be dramatic. This result is mostly attributed to the weakening of the fiber-matrix interface induced by the water aging at high temperature, which consequently affects flexural and impact properties. SEM observations confirm the irreversible damage observed in water uptake experiments. Good interfacial adhesion between fiber glass and epoxy resin is observed for unaged specimens, whereas completely clean fibers are seen for specimens water aged at 80 degrees C, indicating that the fiber-matrix interface is completely removed as a result of this aging condition.