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Glass fiber reinforced epoxy pultrusions were made with a range of fiber volume fractions. They were immersed in water at temperatures in the range 23 to 100°C until saturated, and their dielectric properties measured. Tests on the saturated resins themselves indicated that 60 to 75% of the water was concentrated in disk-shaped regions. The remainder of the water was probably molecularly dispersed; the proportion of this phase depended on the presence of polar groups in the polymer. In the case of the composites, the water provided conducting paths, probably caused by the inter-connection of regions of water concentration at the fiber-matrix interface by the water “disks” that exist in the resin. Dielectric tests appear thus to be a potent tool for providing information about the morphology of resins and composites containing water. In the absence of significant conducting paths, the permittivity obeys simple mixture rules, and the mixture rule giving the best fit to the experimental results gives information about the morphology of the dispersed phase in a composite.
Professor, University of Toronto, Ontario
Materials science engineer, Digital Equipment Canada Ltd., Kanata, Ontario
Stock #: CTR10270J