The Dielectric properties of polypropylene/Na$^+$ montmorillonite nanoclays upon heating and cooling

The dielectric properties of polypropylene/Na$^+$ montmorillonite nanoclay composites have been studied under conditions of heating and cooling. The $\varepsilon(T)$ and $\operatorname{tg}\delta(T)$ parameters have been measured as functions of temperature at frequencies of 10$^3$–10$^6$ Hz in the heating–cooling mode. A comparative analysis of the measured and calculated $\varepsilon$ parameters reveals that the best agreement between the theory and experiment has been provided by the Lichteneker model. As has been established, the values of $\varepsilon$ parameter decrease with an increase in the frequency to 6 $\times$ 10$^4$ Hz, then increase, while the dielectric losses $\operatorname{tg}\delta(\nu)$ are characterized by curves with a diffused maximum at 10$^4$ Hz, which increases with a rise in the nanomontmorillonite filler content. As has been shown, high montmorillonite concentrations in polypropylene favor the acceleration of dipole–relaxation processes and associated dielectric losses, as well as the whole conductivity of nanocomposites.