Water-vapor adsorption on calcium-boroaluminosilicate glass fibers

The water-vapor adsorption isotherms of E-glass fibers were measured as a function of their aging in humid and aqueous environments, and of the amount of B₂O₃ in the glass composition. The specific surface area for adsorption was determined, independently, using inert gas adsorption, while X-ray photoelectron spectroscopy (XPS) was used to characterize the surface composition. In contrast to silica, where submonolayer coverage is observed in the low pressure range of the isotherm, these multicomponent glasses adsorbed the equivalent of 1 to 3 layers of water. The shape of the isotherms revealed that multilayer adsorption of water occurs on the fiber surfaces before the formation of a complete monolayer, i.e., water adsorption on these glass fibers was non-uniform, in general. It was found that the aging of these fibers in humid or aqueous environments greatly enhanced their capacity to adsorb water at low pressure, but the B₂O₃ content of the fibers had little effect.