Long-term durability of thermoset composites in seawater environment

The long-term durability of E-glass/epoxy and E-glass/polyurethane composites in seawater environment were investigated. Samples were conditioned for ninety months (7.5 years) in seawater at room temperature and at an elevated temperature of 65 °C. Changes in mechanical properties are reported and discussed. At room temperature, the tensile strength of the glass/epoxy composite decreased at a very low rate to 94% of its original strength after 7.5 years of immersion in seawater. At an elevated temperature of 65 °C, the strength decreased rapidly to 53% of its original value after five years, then decreased by only 1% between five and seven and a half years. The strength of the E-glass/polyurethane composite started to decline immediately and also reached bottom after five years of immersion where the strength dropped by 34% at room temperature and by 63% at 65 °C. No significant change was observed in the tensile modulus of both composites. The strain-at-failure of both composites increased gradually with water absorption, then dropped to about 50% of its original value after ninety months. After extended exposure to seawater, both composites exhibited brittle failure; and results show that the elevated temperature accelerated the degradation in the matrix and at the fiber/matrix interface. However, it is noted that at room temperature the E-glass/epoxy retained 94% of its strength and the E-glass/polyurethane retained nearly 63% of its strength after 7.5 years of immersion in seawater.