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, tan 𝛿 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.
Volume 42 | Issue 3