A Study of Electrostatic Charges Produced during Mastication of Rubber and of GR-S

Abstract

A new electrostatic field strength meter has been described which measures and records, not only the magnitude of electrostatic fields, but also their polarity. This device has been used in a study of the mastication of rubber, and has furnished data which indicate that rubber becomes less negative, and may actually become positive, as mastication proceeds ; this indicates in turn an oxidation of the molecules as well as an electronic rearrangement and orientation of the rubber molecular chains. Data on GR-S polymerized at different temperatures show entirely different electrostatic breakdown curves, which, with other physical characteristics, indicate unusual properties of the crude low-temperature polymers; e.g., high molar weight, long-chain molecules, already or easily oriented, which do not oxidize or break up appreciably on mastication. A partial correlation of Mooney viscosity and electrostatic contact-potential and field strength has been shown for rubber and GR-S which have been masticated on a rubber mill. The new electrostatic-field strength meter shows promise as a new tool which can be used in processing control, and also as a research instrument for obtaining fundamental information on mastication, pigment dispersion and incorporation, as well as an aid in forming new concepts concerning the structure of matter.

Electrical Contact Potentials in Banbury Mixing

“…It is well knowm that the breakdown of rubber by mastication is an oxidation process; how-ever, the mechanism of the plasticizing action of the chemical plasticizers or peptizers, as they are often called, is not so well knowm. In a previous paper (3), it was shown that as rubber w-as masticated the electrical potential went from a highly negative value to a positive value. This loss of electrons, or increase in positive charge, indicated that the breakdown of rubber by mastication was an oxidation reaction.…”

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.…”

Elastomers

“…A new "electrostatic probe" and associated equipment have been described for measuring and recording the changes in electrical potential of the rubber batch in the Banbury mixer (66). By this means the breakdown of the rubber and the state of incorporation of the pigment, oils, and other ingredients can be followed without raising the ram.…”