Salt sorption on regenerated cellulosic fibers: electrokinetic measurements

Abstract

Streaming potential measurements were conducted on lyocell and viscose fibers, to determine the relative order in sorption extents of salt cations and anions. The sorption of K+ was greater than Na+ ions, and the sorption extents of the anions, Cl− and Br−, were similar. Previously, we had examined accessibility of the same ions in the fibers, and found them to follow the order: K+ < Na+ and Cl− < Br−. From these two contrasting results, we find that the mode of salt interaction with cellulose, from aqueous solutions, changes with the salt concentration. At low concentrations, the interaction is governed by ion-exchange processes with the cellulose carboxyl groups and the Donnan equilibrium; but at higher concentrations, the interaction is a function of the mobility (or diffusivity) of the ions. Thus, sorption and accessibility of cellulose fibers as measured with salts may not apply for other solutes, and conversely, similar studies with other probe molecules may not be relevant for salts.