Structure and properties of electrically conducting composites consisting of alternating layers of pure polypropylene and polypropylene with a carbon black filler

Electrically conducting composites consisting of alternating polypropylene (PP) and carbon black (CB)-filled polypropylene (PPCB) layers were prepared by multilayered coextrusion. The co-continuous structure with selective location of CB in PPCB layers was controllable by changing the number of multiplying elements, and decreased the percolation threshold and electrical resistivity of multilayered composites because of the double percolation effect. This double percolation could be achieved in a single polymer matrix using multilayered coextrusion, whereas it can only be produced in two different polymeric matrices by conventional approaches. Results showed that the dispersion of CB aggregates in PPCB layers was greatly affected by the shearing forces induced by the horizontal spreading flow and vertical recombination occurring during the multilayered coextrusion. The electrical resistivity, positive temperature coefficient effect and mechanical properties of multilayered composites depended strongly on their number of layers. A brittle-ductile transition occurred in PPCB layer compared with the conventional composites. The interesting positive and negative temperature coefficient effects occurred during crystallization and depended on the number of layers. A mechanism is proposed to explain these phenomena.