A Comparison of the Viscoelastic and Dielectric Properties of Natural Rubber—Sulfur Systems

Abstract

AbstractThis paper presents a comparison of viscoelastic and dielectric retardation time spectra of a rubber‐sulfur system with a sulfur concentration ranging from 1.75 to 16.4%. The viscoelastic spectra were obtained from creep measurements which were carried out in the time interval 3 × 10−2 to 5 × 10+1 sec. and a temperature range from −40°C. to + 70°C. The dielectric spectra were derived from measurements of the frequency dependence of the real and imaginary part of the complex dielectric constant in the frequency range 3 × 101 to 3 × 104 cps or temperatures between −50° and +35°C. The temperature‐time superposition principle was used in the derivation of the spectra. The following conclusions may be deduced from the comparison: (1) The retardation times corresponding to the spectral maximas for mechanical measurements are displaced by several orders toward longer times with respect to those for dielectric measurements. (2) The reference temperatures T determined from the WLF equation are higher for viscoelastic measurements than for dielectric measurements, especially for samples with a higher sulfur content. (3) The viscoelastic spectra become narrower, while the dielectric spectra broaden with increasing sulfur content. Further, it was ascertained that the results of dielectric measurements correspond to the presumption that the logarithmie retardation time spectrum has the Gaussian form in logarithmic time scale.