Elsevier

European Polymer Journal

Volume 37, Issue 6, June 2001, Pages 1139-1143
European Polymer Journal

A conductive rubber based on EPDM and polyaniline: I. Doping method effect

https://doi.org/10.1016/S0014-3057(00)00235-4Get rights and content

Abstract

In this work a methodology is described to prepare blends of ethylene–propylene-diene (EPDM) rubber and polyaniline (PAni) by mechanical mixture. PAni was synthesized by chemical polymerization in a pilot-plant scale and doped with dodecylbenzene sulfonic acid (PAni–DBSA). Different doping methods were used: solution, grinding in a mortar and reactive processing. PAni–DBSA acts simultaneously as reinforcement and conductive filler for EPDM rubber, independently of the doping method. Swelling measurements for blends showed that EPDM is partially soluble, evidencing partial interaction between the components. We show that a conductive rubber based on EPDM and PAni can be prepared by reactive processing without a crosslinking agent.

Introduction

Incorporation of conductive polymers into a hosting polymer substrate, forming a blend, composite or interpenetrated bulk network has been widely used as an approach to combine electronic conductivity with desirable mechanical strength of polymers [1], [2], [3]. Polyaniline (PAni) has been intensively studied as a practical conducting polymer material because of its good conductivity, stability and easy synthesis [4]. Doping PAni with inorganic acids produces an unstable and insoluble material [5]. However, an organic protonic acid doping method resulting in a thermally stable doped complex has recently achieved great progress towards stability [6]. The use of bulky protonic acids, such as p-toluene sulfonic acid, makes PAni soluble in organic solvents in the doped state and its processing properties are greatly improved [7]. Similarly, dodecylbenzene sulfonic acid (DBSA) has been also used as dopant resulting in a conducting complex, which is also soluble in organic solvents [8]. In blends the protonic acid also enhances the compatibility of PAni with conventional polymers [9]. The conventional method for doping PAni is by mixture in a liquid medium [10]. Recently, several researches reported a “thermal doping” process, in which PAni base emeraldine and DBSA are mixed at high temperature and the formation of a PAni–DBSA conductive complex occurs. The presence of unbound, excess DBSA, only physically mixed with PAni, leads to a dispersion of PAni particles in DBSA, a paste that is mainly ionically conducting. Heating causes solidification of the paste, and the PAni–DBSA complex becomes electrically conducting (1–10 S cm−1). If large amounts of excess DBSA are used, a plasticized complex is obtained [11], [12], [13].

In the present study a conductive PAni–DBSA complex prepared by solution, grinding in a mortar and reactive processing and its blends with the elastomer ethylene–propylene-diene (EPDM) prepared by mechanical mixture were investigated. The effect of the PAni–DBSA doping method was analyzed. The aim of this study is to obtain an electrically conductive rubber material by reactive processing.

Section snippets

Polyaniline preparation

HCl doped PAni was prepared by a pilot-plant scale adaptation [14] of a previously published work [15]. The product was neutralised with an aqueous NH4OH solution, resulting in PAni emeraldine base (EB). Doping was carried out using three methodologies: (i) stirring EB for 24 h in a 1.5 mol l−1 solution of DBSA; (ii) grinding in a mortar EB and DBSA in a 1:2 ratio and (iii) doping EB with DBSA (1:2) by reactive processing in an internal mixer chamber of a Haake rheometer 600 (cam rotors) at

Results and discussion

PAni doping was done by the three methods described, blends were prepared and the materials were characterised. EPDM/PAni–DBSA blends using PAni doped by the three different methods were prepared in the same mixer in the conditions described in the experimental part and the variation of the torque as a function of processing time for the preparation was measured (Fig. 1). The difference observed in the curves depend on the PAni used and can be discussed in terms of the interaction among the

Conclusions

PAni–DBSA acts as reinforcement and conductive filler in blends with EPDM, contributing to the formation of a network which inhibits EPDM solubilization. Thus, a conductive rubber compound was prepared without the use of a crosslinking agent. The material presents mechanical properties suitable for use as reinforced rubber. Good conductive properties were found for blends with 30% (w/w) of PAni–DBSA, independently of the doping method used. This concentration threshold was previously observed

Acknowledgements

Authors thank the financial support from FINEP and FAPESP (Proc. 96/09983-6) and RF acknowledges a fellowship from FAPESP (Proc. 95/1457-4). We also thank the samples supplied by P.S. de Freitas (polyaniline syntheses), Hoechst do Brasil S.A., Solvay, Bann Quı́mica and Nitriflex S.A.

References (19)

  • A.G MacDiarmid et al.

    Synth Met

    (1987)
  • Y Cao et al.

    Synth Met

    (1993)
  • O.T Ikkala et al.

    Synth Met

    (1995)
  • K Levon et al.

    Polymer

    (1995)
  • O.T Ikkala et al.

    Synth Met

    (1995)
  • W.A Gazotti et al.

    Synth Met

    (1996)
  • R Faez et al.

    Polymer

    (1999)
  • A Andreatta et al.

    Polym Commun

    (1990)
  • De Paoli M-A, Waltman RJ, Diaz AF, Bargon J, J Chem Soc Chem Commun...
There are more references available in the full text version of this article.

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