Influence of high levels of water absorption on the resistivity and dielectric permittivity of epoxy composites

We studied the effects of water absorption (up to 1 wt%) on the dielectric properties of mica/glass/epoxy laminated composites used for high-voltage insulation. The DC resistivity, the dielectric constant and the dielectric loss were studied in the 10(-2)-10(6) Hz range, as a function of water uptake. The dielectric characteristics are strongly affected by water ingress. Upon water sorption the resistivity decreases by several orders of magnitude. Its variation is well described by a percolation law. The low-frequency permittivity rises to very large values. The large increase in the permittivity is related to an electrode polarisation mechanism. (c) 2005 Elsevier Ltd. All rights reserved.