Water uptake at 25°C is measured for unsaturated polyester matrix and glass fiber composites as a function of time. Dielectric measurement in the frequency range of 1 MHz-1 GHz has been performed on the specimens during the water absorption process. The dielectric constant decreases as the frequency increases for matrix and composites. The dielectric constant of unsaturated polyester is lower than their composites based on glass fibers. A Fickian diffusion model is applied for water absorption studies, and the effective diffusion coefficient is calculated for each sample. An empirical model describing the increase in dielectric constant with water absorption is proposed.
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