Dielectric vulcametry

Dielectric properties such as the complex permittivity ε∗ (real part ε′ and imaginary part ε″) and tan have previously been reported for a large number of polymeric materials at different frequencies and temperatures. The manner in which the crosslinking reactions influence the dielectric properties of rubber materials has on the other hand been very sparsely investigated. Sulphur-cured and peroxide-cured model compounds of some polydienes (NR, IR, BR and NBR) have here been studied and it has been found that the width of the dispersion curve correlates fairly well with the crosslink density irrespective of the composition of the curing system. During thermo-oxidative ageing (85 °C) of sulphur-cured natural rubber, a large widening of the dispersion curve (tan δ) is found at frequencies lower than 1 MHz if the measurements are made at room temperature.