Effect of Motion of Impurity Ions on Electrical Properties of Polymer Materials

In melt-crystallized polymers, free spaces with inhomogeneous size exist between crystallites. These free spaces results from non-crystalline polymer molecules which are not taken in into the crystallites. These free spaces become a path for impurity ions to move. The ionic motion along such path with the inhomogeneity affects the electrical properties of polymer materials. In order to study the effect of such ionic motions on energy loss, the interaction between ionic motion and inhomogeneous structure on the electrical properties was investigated. For this objective, the permittivity and the electric modulus were observed for isotactic poly(propylene) (iPP) and plasticized poly(vinyl chloride) with dioctyl phthalate (p-PVC) by means of the Broadband Dielectric Spectroscopy. A simple DC conduction is observed for p-PVC. However, for the iPP, another ionic motion appears on lower frequency side in addition to the DC conduction at high temperature. This change of ionic motion is considered to be caused by a phase transition in crystalline phase accompanied by a structural change in the non-crystalline part.