Softer Conductive Rubber Compounds by Elastomer Blending

Abstract

Abstract Carbon black parameters that impart high conductivity in elastomer compounds, i.e., high surface area, structure, and porosity also increase compound viscosity and thus cause processing problems. In the present study, an attempt has been made to circumvent the problem by modification of the elastomer phase. Many black loaded elastomer pairs show maxima in their electrical conductivity-composition curves; the maxima are several orders of magnitude higher than that exhibited by the component elastomers. Moreover, the curves of viscosity and hardness vs. elastomer composition show either flatter maxima or even minima in some cases. Thus, conductivity with respect to the single elastomers can be increased without corresponding increases in viscosity or hardness values. The above phenomenon can be explained by elastic modulus and electron microscope investigations of black loaded elastomer blends. Elastic modulus data of black loaded blends show increased agglomeration of the carbon network in the case of incompatible elastomer pairs. Electron microscopic examination of these compounds reveals a redistribution of the carbon black. Redistribution occurs from the less reactive or less viscous polymer to the blend interface, even when black is added to the former. Accumulation of black at the interface reduces the gap width by increasing the number of contact points to result in an overall conductivity increase. The conditions for maximum conductivity were determined from the conductivity-composition curves of several elastomer pairs. It was concluded that the redistribution of carbon black, which causes the conductivity increase, can take place if the elastomers in a pair are highly incompatible and differ widely in their black interaction (e.g., NBR-CIIR), or in their viscosity (e.g., NR-CR).