Zeta‐potential Studies in Cellulose Fibre–Aqueous Electrolyte Solution Systems

Abstract

Zeta‐potential studies of cotton and viscose rayon fibres in aqueous sodium and potassium chloride solutions of different concentrations have been carried out using the streaming‐potential method. The Eversole and Boardman equation, which relates the measured zeta potential to the thickness of the electrical double layer, has been found to be valid in all cases. Using the surface‐potential values calculated from this equation, the surface‐charge densities in these fibres have been estimated. They are in good agreement with the theoretical surface‐charge densities calculated from data on the carboxyl‐group content of these fibres and the BET nitrogen surface areas for the water‐swollen uncollapsed fibres. Two alternative explanations for the apparent increase in surface‐charge density with decrease in the zeta potential have been given, without assuming that the anions are absorbed. The variation in zeta potential with increasing carboxyl‐group content in samples of oxycellulose has been explained in terms of changes in the degree of dissociation of carboxyl groups with increasing carboxyl content, and an increase in the surface area of the cellulose fibre on oxidation. Studies of the zeta potentials in Form‐W and Form‐D formaldehyde‐crosslinked cotton fibres have indicated that the zeta potential increases with increase in formaldehyde content with Form‐D fibres. This result can be explained in terms of the decrease in the surface area of Form‐D cottons with increase in the content of bound formaldehyde.