Dynamic electromechanical measurements of carbon black loaded SBR

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Virginia Tech

The major objectives of this study were to examine electrical and electromechanical properties of SBR filled with carbon black in the 0-70 phr range. The experiments were divided into four parts: dielectric measurement, loss modulus and phase angle measurements, temperature rise measurement during stress cycling, and dynamic conductivity measurement.

It is established that there are three distinct conduction regimes existing at carbon black loadings below, at, and above the percolation threshold. Characteristics of dielectric dispersion depend strongly on carbon black loading and frequency. Dielectric and AC conductivity measurements are shown to provide a nondestructive method to explore the carbon black network inside the rubber.

Both loss modulus and phase angle are related to hysteresis properties, and to temperature rise due to compressive cycling. Measurements of these parameters will be discussed in detail, as functions of carbon black loading, stress and strain amplitudes, and oscillation frequency. These and other results can be understood in terms of the mechanics of the carbon black network. The variation of conductivity with strain amplitude is related directly to the interplay between the "persistent" and "transient" fractions of carbon black network. It is shown that, owing to its experimental accuracy and great sensitivity to carbon black network changes, the dynamic conductivity measurement is preferable to traditional modulus measurements for determining certain dynamic properties of carbon black filled rubbers.