Conductive polymer composites: Influence of extrusion conditions on positive temperature coefficient effect of poly(butylene terephthalate)/poly(olefin)-carbon black blends

Processing conditions determine both the morphology and the carbon black (CB) distribution in conductive polymer composites (CPCs). Good control of these parameters is essential to obtain reproducible electrical properties. We found that for extruded tapes of poly(butylene terephthalate) (PBT)/poly(olefin) (OLE)-CB blends, an increase of both processing temperature and screw speed leads to a significant decrease of resistivity. This shift factor, more important with PBT/poly(ethylene)-CB than with PBT/poly(ethylene-co-ethyl acrylate)-CB, is attributed to viscosity variations of all compounds. A decrease of viscosity promotes CB aggregation at the PBT/OLE interface and creates larger conductive channels by coalescence. Nevertheless, the CB concentration effect appears predominant compared to the morphology effect to explain resistivity variations. This interesting finding can be used either to improve reproducibility of electrical properties or to adjust electrical properties without changing CPC formulation. (C) 2003 Wiley Periodicals, Inc.