E-Glass/Vinylester Composites in Aqueous Environments - I: Experimental Results

2- and 4-layered specimens of E-Glass/Vinylester fabricated from uniaxial, biaxial, and triaxial, non-woven fabrics processed using the resin infusion process are immersed in deionized water at 23°C (73°F) and 60°C (140°F), and a potassium based pH 10 buffer at 73°F, for a period of 57 weeks in order to investigate durability in aqueous environments. It is shown that the coefficients of apparent diffusion and levels of moisture gain are the highest for the deionized water immersed samples at 60°C (140°F), and this results in the highest levels of tensile strength and modulus degradation. Tensile tests show the presence of an aqueous medium based post-cure that competes with the conventionally recognized mechanisms of deterioration in the resin, at the level of the fiber-matrix interface, and in the fiber, resulting in a retardation of absolute level of effects. It is also shown that effects of the immersion are different in the warp and fill directions and can in fact be affected by intricacies of the fabric architecture and thickness. It is shown that damage takes place through interface debonding and degradation as well as fiber pitting, and cracking, each of which serve as the means for renewed absorption of water resulting in moisture uptake at levels above the initial plateau. Effects of immersion on short-beam-shear strength and glass transition temperature are also elucidated.[PUBLICATION ABSTRACT]