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 degrees 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 degrees 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 degrees 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.