Electrostatic and Tensile Properties of Rubber and GR-S at Elevated Temperatures

Abstract

This paper describes a new apparatus for measuring electrostatic contact potentials on various materials at elevated temperatures. In this apparatus, the electrostatic charge, acquired by rolling a steel ball down the surface of a rubber test specimen on a heated inclined plane, is measured when the ball drops into the cup of a suitable measuring device such as our electrostatic modulator. With this instrument the contact potentials of both rubber and GR-S was found to become highly negative at elevated temperatures. This apparent ``boiling off'' of electrons and resultant disruption of electrostatic attractive forces within the material is much greater for GR-S than for rubber and probably accounts for the much greater decrease in tensile of GR-S over rubber at elevated temperatures, and is further confirmation of the electrostatic contact potential theory of reinforcement. By the further application of this theory suitably dispersed compounding materials, which are in effect highly positive at elevated temperatures such as certain proteins, finely divided silica and sodium silicate, have been found to increase substantially the hot tensile strengths of GR-S compounds.