CONDUCTIVITY VARIATION INDUCED BY SOLVENT SWELLING OF AN ELASTOMER-CARBON BLACK-GRAPHITE COMPOSITE

The behavior of a polybutadiene-carbon black composite entering into c ontact with organic solvents and gasoline was investigated. The compos ite used has a conductivity of 3.0 +/- 0.1 Omega(-1) cm(-1). However, if it comes into contact with organic solvents (gasoline, for instance ) the matrix absorbs them and consequently swells. This swelling cause s the separation of the carbon particles and the concomitant diminutio n of the composite conductivity. During the tests performed, the resis tivity of the composite grows exponentially with the exposure time to solvents. Typically, the material samples show a reduction of approxim ately 30% of its initial conductivity after only 1.5 min of exposure t o solvents. Also, it was observed that the rate at which the conductiv ity decreases is related to the chemical nature of the solvent used in the test. To model the drop on composite conductivity induced by solv ent swelling we use an effective media percolation approach. This appr oach was adapted to the needs of our experiments by modifying the defi nition of one of its main parameters (the critical volume of the low-c onductivity fraction). The experimental data were successfully describ ed by this model. Finally, the test performed shows that this composit e is a very promising material that can be employed, for example, in v arious security and control devices to warning of accidental organic s olvent or hydrocarbon leaks in pipelines or containers of chemical ind ustries and refineries. (C) 1997 John Wiley & Sons, Inc.