Pigment Contact Potentials and Reinforcement

Abstract

1. A new apparatus has been described for measuring the contact potential of powdered reinforcing pigments. 2. With this apparatus, contact potentials on MPC and FT blacks, fine and coarse particle size zinc oxides, whiting, and barytes show correlation with their reinforcing properties in natural rubber and cis-1 ,4-polybutadiene rubber. 3. Contact potentials of Hi-Sil, Suprex clay, coated zinc oxides and coated calcium carbonate pigments showed no correlation with their reinforcing properties in rubber. 4. Contact potentials on the minerals, diamond, quartz, zinc oxide, calcite and barite correlated with the reinforcing properties of their pigment counterparts. 5. Contact potentials of the minerals also correlated with Mohs hardness. 6. Contact potentials on coated zinc oxide pigments correlated with their improved processing properties in rubber. 7. A new apparatus has been described for measuring the contact potentials of cured stocks in which cut surfaces, rather than molded surfaces, are used. Greater accuracy is possible due to the elimination of surface bloom and other surface contamination. 8. Contact potentials measured on the cut surface of cis-1,4-polybutadiene stocks containing various pigments showed good correlation with their reinforcing properties, thus confirming, with this new rubber, the Electrostatic Contact Potential Theory of Reinforcement.