Factors Affecting the Zeta Potential at Wool Fiber Surfaces

Abstract

A streaming potential method has been used to determine the zeta potential at the surface of wool fibers in a supporting electrolyte solution. The zeta potential gives a measure of the average charge density at the surface of shear and, when measured as a function of pH, yields a titration curve for the fiber surface. The reproducibility of the curves for a particular wool sample is now such that zeta potential determination provides a means of assessing chemical reactions at the fiber surface through changes in surface charge. The technique has been applied to studies of the chlorine/Hercosett shrinkproofing process.

The shapes of the curves and the pH of the isoelectric point can be significantly affected by the choice of cleaning procedures adopted to remove contaminants. In addition, the state of the surface changes with time; this aging process leads to a more negative surface through atmospheric oxidation. Chemical oxidation by acid chlori nation of disulphide groups brings about a large excess of anions and a negative surface. Subsequent modification by deposition of a cationic polymer, as in the chlorine/ Hercosett process, results in a more positive surface. However, the interaction between the polymer and the wool causes the new surface to be less positive than for Hercosett film coated on a glass substrate.