Available online at www.sciencedirect.com Synthetic Metals 157 (2007) 1071–1073 From conductive polymer composites with controlled morphology to smart materials G. Boiteux a,∗ , Ye.P. Mamunya b , E.V. Lebedev b , A. Adamczewski a , C. Boullanger a , P. Cassagnau a , G. Seytre a a IMP UMR CNRS 5627, Laboratoire des Mat´ eriaux Polym` eres et Biomat´ eriaux, UCB-Lyon 1, 69 622 Villeurbanne Cedex, France b Institute of Macromolecular Chemistry, National Academy of Sciences, Kiev, Ukraine 48, Kharkivske Chausse, 02160 Kyiv, Ukraine Received 23 March 2007; received in revised form 6 November 2007; accepted 9 November 2007 Available online 21 December 2007 Abstract Conductive polymer composites (CPC) based on insulating matrix with conductive dispersed fillers are extensively studied since many years. A specific feature of such materials is a value of the filler content corresponding to the percolation threshold where a sharp transition insulat- ing/conductive state occurs. The objective of this work is first the study of percolation phenomena in composites based on polypropylene (PP), on copolymers of polyamides (CPA) and polymer blends PP/CPA filled with dispersed iron (Fe) related to their structure but also to pay atten- tion to their specific behaviour in temperature so-called PTC effect which can be controlled according the composition and the structure in the heterogeneous polymer matrix of the composites to elaborate intelligent/smart materials. © 2007 Elsevier B.V. All rights reserved. Keywords: Conductivity; PTC effect; Metallic filler; Polymer blend 1. Introduction Conductive polymer composites (CPC) are an interesting field of research for different applications in particular, during the last years, as smart materials presenting PTC effect: that is to say an interesting reversible temperature dependence of their conductivity. The studies of this effect concern a large choice of thermoplastic or thermoset matrices filled generally with carbon black [1] but more recently metal plated ceramic filler [2] and metallic particles to support higher intensity and voltage working constraints [3–6]. The perspectives of applica- tions as smart materials are namely as temperature sensors and disruptor devices, materials for production of thermistors, self- regulating heaters, etc. A PTC element looks like a conductive sheet which, under heating, presents a drastic change of its resis- tivity at so-called commutation temperature T c within a narrow range of temperature and which, under cooling, found again its conductive state. ∗ Corresponding author. Tel.: +33 4 72 44 85 64; fax: +33 4 78 89 25 83. E-mail addresses: Gisele.Boiteux@univ-lyon1.fr (G. Boiteux), yemamun@i.kiev.ua (Ye.P. Mamunya). In this work, polypropylene PP or blends PP/CPA of polypropylene with copolymers of polyamides: 6, 6.6 and 6.10 are mixed with conductive iron particles to elaborate con- ductive polymer composites (CPC) which can present a PTC effect to be used in particular for a specific current limited function. 2. Materials and experimental Polypropylene of grade 2 called PP was supplied by Exxon Mobil Chemical (PPg2, MFI = 2 g/10 min is a commercial polypropylene, Code EMB76384, T m = 162 ◦ C). It contains cer- tainly some additive lowering the melting temperature of pure PP which is 165 ◦ C. Copolymers of polyamides were synthesized by IMC “Petru Poni” in Romania (CPA, MFI = 11.8 g/10 min, T m = 125–135 ◦ C). They are statistic aliphatic copolyamides obtained by direct melt polycondensation of monomers in a molar ratio -caprolactam:adipic acid:1,6-hexane diamine: sebacic acid = 1:0.1:0.45:0.35, yielding in a composition PA6: PA6.6:PA6.10=70:6:24. It has such a low melting point due to its statistic distribution of the various PA sequences which 0379-6779/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.synthmet.2007.11.003