THERMALLY STIMULATED CURRENT OF HEAT-TREATED POLYACRYLONITRILE

Abstract

Thermally stimulated current (TSC) of polyacrylonitrile (PAN) films heat-treated at elevated temperatures in air and in vacuum has been investigated. In the TSC spectra of solvent cast PAN films, the current peak due to residual solvent was observed. The residual solvent could be removed by heat treatment in vacuum at 200°C for 60min. The TSC spectrum obtained for a solvent free PAN film was characterized by two current peaks observed at 110°C (αII peak) and 150°C (αI peak) due to the dipolar relaxations in the paracrystalline and amorphous phases, respectively. The amount of polarization calculated from TSC was in good agreement with theoretical value calculated from the dipolar orientation of nitril groups.The αII peak increased in the early stage of heat treatment at 230°C, while the αI peak decreased rapidly. The total polarization calculated from the both peaks decreased linearly with decreasing amount of nitril groups in a PAN film. It was found that a PAN film heat-treated at 230°C in air for longer times than about 200min did not show a significant TSC, although it was confirmed by infrared analysis that about 20% of nitril groups in PAN still remained after the heat treatment. This fact indicates that the pendant nitril groups of PAN heat-treated for prolonged time were immobilized by neighboring cyclized rigid segments and could not contribute to polarization.