The effect of swelling and temperature on the electrical and mechanical behaviour of a filled rubber

The effect of swelling and temperature on the electrical resistivity of highly carbon black filled elastomers under strain is investigated. It is shown that swelling, even to a modest extent of less than 10%, has a marked effect upon the resistivity. The effect of a linear expansion due to swelling is much more marked than an equivalent tensile extension. The increase in electrical resistivity with swelling is also much greater than the increase produced by an equivalent reduction in the volume fraction of the carbon black alone. The increase depends upon the chemical nature of the swelling agent, and there is a relatively small effect of temperature induced volume change on resistivity, contrasting markedly with the large effect of the same volume increase produced by swelling. These observations suggest that on swelling there is a preferential migration of the solvent to the rubber/filler interfaces. This will push the carbon black aggregates apart and lead to a dramatic increase in the resistivity across the interface. There are also indications that at elevated temperatures the filler/rubber interactions are reduced.