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Keywords:

  • polymer blends;
  • conductivity;
  • PTC effect;
  • carbon black

Abstract

We have studied the influence of the addition of poly(butylene terephthalate) (PBT) to poly(ethylene-co-ethyl acrylate)-carbon black (EEA-CB) on the electrical properties of the blends, namely the resistivity and power dissipation of the monophasic and diphasic systems. The morphology of the latter blend is characterized by two interpenetrated immiscible phases which provide a good thermal stability to the composite up to at least 170 °C. Power can be regularly delivered without a negative temperature coefficient (NTC) effect at 100 °C where poly(ethylene-co-ethyl acrylate) melts. However, the significant decrease of positive temperature coefficient (PTC) amplitude compared to the monophasic systems reduces the self-regulating heating ability. The PTC effect amplitude decrease was studied by some of its known origins (thermal expansion, melting of crystalline phase, carbon black localization). Correlation of the composites resistivity with linear expansion, the melting process of EEA, and the volume expansion of PBT, show that none of these parameters can alone explain the electrical properties' evolution with temperature. Our interpretation of the PTC effect amplitude decrease is based on the PBT matrix lower thermal expansion and on the increased carbon black content located at the interface. Copyright © 2003 John Wiley & Sons, Ltd.