Abstract
Electrical properties of butyl rubber filled with General Purpose Furnace (GPF) carbon black were studied. The carbon black concentration (X) in the compound was X = 40, 60, 70, 80, and 100 parts by weight per hundred parts by weight of rubber (phr). The corresponding volume fractions of GPF carbon black were 0.447 +/- 0.022, 0.548 +/- 0.027, 0.586 +/- 0.029, 0.618 +/- 0.031 and 0.669 +/- 0.034, respectively. The concentration dependence of conductivity (sigma) at constant temperature showed that sigma follows a percolation theory; sigma alpha (X - X-0)(gamma), where X-0 is the concentration at percolation threshold. The exponent gamma was found as 6.6 (at room temperature 30 degrees C). This value agrees with other experimental values obtained by many authors for different rubber-carbon black systems. Electron tunneling between the aggregates, which are dispersed in the insulator rubber, was mainly the conduction process proposed at constant temperature in the butyl-GPF carbon black composites. Temperature dependence of conductivity was investigated in the temperature range from 30 degrees C up to 120 degrees C. All samples exhibit negative temperature coefficients of conductivity (NTCC). The values obtained are - 0.130 degrees C-1, -0.019 degrees C-1, - 0.0082 degrees C-1, - 0.0094 degrees C-1, and - 0.072 degrees C-1 for carbon black concentrations of 40 phr, 60 phr, 70 phr, 80 phr, and 100 phr, respectively. The samples of concentrations 40 phr and 60 phr have also positive temperature coefficients of conductivity (PTCC) of values + 0.031 and + 0.013, respectively. Electrical conduction at different temperatures showed various mechanisms depending on the carbon black concentration and/or the interval of temperature. The hopping conduction mechanism was noticed at the lower temperature region while carrier thermal activation mechanisms were recorded at the higher temperature range.