Effect of heat treatment on dielectric relaxation of polyacrylonitrile: Reversible thermally induced structural change

The effect of heat treatment on the dielectric relaxation of polyacrylonitrile (PAN) was studied. Dielectric measurements, in the frequency range 0.1–100 kHz and temperature range 30–170°C, on PAN heat treated at two temperatures (120 and 160°C) and the untreated PAN are reported. The loss peak height, the dielectric relaxation strength, loss peak width, and the loss peak temperature were found to vary systematically with the temperature of the heat treatment. The changes in dielectric relaxation produced by heat treatment at the higher temperature (i.e., 160°C) were considerably less than those produced by heat treatment at 120°C. The results are discussed and attributed to the variation of the degree of bound nitrile groups (through their dipole–dipole interaction) with heat treatment temperature. Heat treatment of the higher temperature (160°C) results in lower degree of bound nitrile groups in the structure than heat treatment at the lower temperature (120°C).