Evaluation of a.c. conductivity behaviour of graphite filled polysulphide modified epoxy composites

Abstract

Composites of epoxy resin having different amounts of graphite particles have been prepared by solution casting method. Temperature dependence of dielectric constant, tan δ and a.c. conductivity was measured in the frequency range, 1–20 kHz, temperature range, 40–180°C for 0.99, 1.96 and 2.91 wt% graphite filled and unfilled epoxy composites. It was observed that the dielectric constant, tanδ and a.c. conductivity increase with increasing temperature. Near the transition temperature the materials show anomalous behaviour for the observed properties. Peaks of dielectric constant, tan δ and a.c. conductivity were observed to shift towards lower temperature with increasing frequency. Clear relaxation (tan δ) peaks around 169°C were observed in epoxy resin, which shifted to lower temperature side on increasing the frequency. Addition of 2.91 wt% graphite shifted the tan δ peaks towards higher temperature side by creating hindrances to the rotation of polymer dipoles. Addition of 2–91 wt% graphite leads to an increased relaxation time τ of dipoles in polysulphide epoxy from 1.44 × 10⁻⁵− 3.92 × 10⁻⁵ (s) at 90°C by creating the hindrance to the rotation of dipoles.