Electrochemical Aspects of Rubber Latex, Compounding Ingredients, and Their Mixtures

The electrophoretic speeds of rubber latex particles as well as of colloidally dispersed compounding agents, e.g., zinc oxide, sulfur, china clay, and mixtures of them as are generally employed in baths for electrodeposition, have been measured in a microcataphoresis cell of the Northrup-Kunitz type. The ζ-potential of latex, calculated from the electrophoretic speeds, is considerably influenced by the presence of the compounding agents. Sulfur sol having the lowest ζ-potential tends to reduce that of latex as well as of others in a mixture, whereas zinc oxide and china clay, which have higher ζ potentials, tend to increase the value for latex. A mixture of zinc oxide and china clay shows the highest (60 mV) ζ-potential compared to latex itself (ζ=28.8mV). The isoelectric point of rubber latex was measured by calculating the ζ-potential from the electrophoretic speed at different pH values, which were maintained by means of Na2CO3⋅NaHCO3 buffers at the higher range and acetate buffers at the lower range. The I.P. was 4.2 and was lowered in the presence of zinc oxide and china clay sols to 3.0 and 3.8, respectively, but increased to 5.1 in the presence of sulfur sol.