Influence of Seawater Absorption on the Hardness of Glass Fiber/Polyester Composite

In the marine industry, glass fibers are commonly used to reinforce polyesters for ship hulls, submarine components, and other marine structures. Isophthalic polyesters are a feasible alternative due to their superior mechanical qualities and added end-of-life scenarios compared to orthophthalic polyesters. However, like other fiber composite systems, glass fiber reinforced polymer (GFRP) composites are also water sensitive. Here, GFRP composites of three different thicknesses are aged under three different immersion periods in seawater (20, 40 and 60 days). All samples are reconditioned and evaluated for hardness following aging. Significant emphasis is placed on the presence of calcium carbonate, over which increases in moisture content irrevocably reduce the composite’s hardness. Compared to untreated material, the hardness of 6, 8, and 10 mm composites decreased by 25.64, 10.92, and 4.63% after the 60-day aging period. This drop is mostly the result of microstructure evolution manifesting as an increase in porosity. Consequently, fiber deterioration, fiber cracks, and degradation of polymer-fiber bonding emerge in the composite, decreasing hardness.