Correlation between rheological and dielectric percolation of conductive carbon black-filled ethylene acrylic elastomer

Abstract

Conductive rubber composites based on ethylene acrylic elastomer (AEM) and conductive carbon black (CCB) were prepared by a two-roll mixing mill. From the transmission electron microscope photomicrographs, the uniform distribution of CCB aggregates and the interconnected CCB aggregates in the AEM matrix were observed. The bound rubber content of unvulcanized rubber was found to increase significantly with increasing CCB content. The effect of CCB concentration on the dynamic viscoelastic properties of AEM matrix was determined using a Rubber Process Analyzer (RPA 2000) in terms of strain sweep and frequency sweep of both uncured and cured AEM/CCB systems. The storage modulus (G′) increased with an increase in CCB loading. In the case of strain sweep, the G′ values decreased with strain amplitude for both the systems, but the G′ was more for cross-linked AEM/CCB systems. The strain dependency of G′ for CCB-filled AEM systems can be explained on the basis of the Payne effect. The complex viscosity (η*) of these systems increased with CCB loading, and it decreased with strain amplitude, which is due to the shear thinning effect. The tan δ for unvulcanized and vulcanized systems increased with the strain; however, the value of tan δ was <1 throughout the experimental strain range, which explains the elastic nature of the cured systems. The G′ increased with angular frequency for both the systems and the tan δ became independent upon the angular frequency after 10 Hz. The alternating current conductivity (σ _AC) increased with an increase in CCB loading at all frequencies and the system achieves the percolation at 20 phr CCB loading, which is in accordance with the rheological percolation. The direct current conductivity (σ_DC) also increased with an increase in CCB concentration.