Electrostatic Properties of Rubber and GR-S

Abstract

A new electrostatic modulator has been described for measuring the electrostatic charges on rubber, synthetic rubber, and various materials. In this apparatus the electrostatic lines of force established between the charged specimen and a stationary electrode plate connected to the grid of an audiofrequency amplifier are cut or modulated at audiofrequency by a small four-bladed, motor-driven fan. This produces in effect an alternating current voltage which can be readily amplified by the audio amplifier and quantitatively measured on a meter in the output circuit. This device, in conjunction with a mirror-surfaced metal plunger system for contacting the rubber samples, has been used to measure the contact potential of various rubber and GR-S compounds. Electrostatic contact potential data are shown for both rubber and GR-S compounds with and without organic and inorganic reinforcing agents, and these data bear out the formulation of an electrostatic contact potential theory of reinforcement in which the reinforcement of rubber and GR-S is explained on the basis of contact potentials and resultant electrostatic attractive forces which exist between the rubber and the reinforcing agents. By the application of this theory, organic materials which have a highly positive electrostatic charge, such as polymerized trimethyldihydroquinoline and Flectol-H (an acetone-aniline condensation product), have been found to increase the tensile strength of the pure-gum type of GR-S compounds as much as fivefold and nearly to double the tensile strength of high zinc oxide loaded GR-S compounds.

Natural and Synthetic Rubbers

“…Havenhill, Carlson, Emery, and Rankin (122,123) described a new electrostatic probe and associated equipment for detecting and recording both the polarity and magnitude of electric charges formed when rubber batches are mixed in a Banbury mixer. These contact potentials produce strong electrostatic fields from which one may obtain fundamental information on the mastication, incorporation, and dispersion of softeners and pigments.…”

Natural and Synthetic Rubbers

“…Havenhill and coworkers (116) describe electrical test equipment for evaluating rubber and associated materials. They found that electric charges are specific for each ingredient, and by means of an electric charge recorder they can follow the breakdown of the rubber, the state of incorporation of pigments, oils, and other ingredients during mixing in an internal mixer without disturbing the operation.…”