Influence of moisture absorption on electrical characteristics of glass-epoxy polymer composite system

The fiber-reinforced polymer (FRP) composites, which are being increasingly used in electrical insulation, should withstand electrical stresses under moist environment. The composites get deteriorated due to the moisture absorption in the working environment. During the moisture absorption process, water ingression into the interior including the polymer reinforcement interface region occurs causing degradation. This significantly contributes to the deterioration of electrical characteristics. To study these, composites having three different volume fractions of fibers were fabricated using the hand lay up technique by stacking two different fabrics, chiefly, woven roving (WR) and chopped stand mat (CSM). While for one set, the top layer was made of CSM and the bottom WR (composite 1), that for the next two, CSM layers were both at the top and bottom while the number of WR that followed these cover layers was either two in one case (composite 2) or three in other (composite 3). The dielectric dissipation factor, dielectric constant and insulation resistance measurements were carried out on these composites at room temperature as well as after subjecting to water absorption up to 96 h. The weight gain for all three types of composites show a linear increasing trend up to 72 h and there after a trend for saturation sets in. Further, it is seen that the dielectric dissipation factor and dielectric constant of the composites increase with increase in the water absorption duration and correspondingly the insulation resistance shows a deteriorating trend. Among the three composites studied, Composite 2 having highest fiber content and hence the least matrix content shows better performance compared to composites 1 and 3.