PTC Effect and Structure of Polymer Composites Based on Polypropylene/Co-Polyamide Blend Filled with Dispersed Iron

The temperature dependence of resistivity, structure and thermal expansion of composites based on polymer blend polypropylene/co-polyamide (PP/CPA) filled with dispersed iron (Fe) has been studied. The dependence of conductivity on filler content shows percolation behavior with the values of the percolation thresholds equal to 5 vol.% for the filled blend PP/CPA-Fe with two steps character of the conductivity curve. The evolution of structure of the composite PP/CPA-Fe demonstrates transition from polymer matrix CPA-Fe with inclusions of PP through co-continuous phases of both CPA-Fe and PP to PP matrix with inclusions of CPA-Fe. Such a structure occurs due to localisation of the filler only in one of the polymer phases, namely in CPA. The PP/CPA-Fe composites demonstrate PTC effect with the presence of a resistivity plateau. In such a system the PTC is caused by the break of the conductive structure of the filler inside the CPA-Fe phase due to the morphological changes in the vicinity of the melting temperature of CPA