Salt sorption on regenerated cellulosic fibers: electrokinetic measurements

Avinash P Manian,Thomas Bechtold,Adisak Jaturapiree

doi:10.1007/s10570-018-1823-2

Avinash P Manian, Thomas Bechtold + Show 1 more

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https://doi.org/10.1007/s10570-018-1823-2

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Journal: Cellulose	Publication Date: May 3, 2018
Citations: 8	License type: open-access

Affiliation: Universität Innsbruck, Phranakhon Rajabhat University

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.

Highlights

The accessibility of fibers to reagents and catalysts influences the uniformity and extent of chemical reactions, in treatments intended to improve their performance
We previously investigated the accessibility of two regenerated cellulosic fibers, viscose (CV) and lyocell (CLY), by measuring the sorption of salts from aqueous solutions of salt–alkali mixtures
The negative zeta potentials are attributed to the dissociation of carboxyl and hydroxyl functional groups present on the cellulosic fibers, and the zeta potential magnitudes vary with the degree of functional group dissociation, and with the degree of sorption of ionic species (Pothan et al 2002; Ribitsch et al 1996, 2001; Stana-Kleinschek et al 2001; StanaKleinschek and Ribitsch 1998)

Summary

Introduction

The accessibility of fibers to reagents and catalysts influences the uniformity and extent of chemical reactions, in treatments intended to improve their performance. It becomes useful to measure fiber accessibility in aqueous media, where the effect of fiber swelling is accounted for; rather than in non-swelling media, such as for example when accessibility is determined by vapor or gas sorption With this in mind, we previously investigated the accessibility of two regenerated cellulosic fibers, viscose (CV) and lyocell (CLY), by measuring the sorption of salts from aqueous solutions of salt–alkali mixtures. Salts were chosen as probe molecules since they do not exhibit chemical affinity for the polymer, and alkalis were added because fiber treatments are often performed in alkaline solutions, and the alkalinity influences fiber swelling. Both CV and CLY are composed of cellulose, and derived from wood pulp through dissolution and reprecipitation (coagulation). CV fibers have a lower degree of polymerization, lower degree of crystallinity, higher swelling degree in water, and exhibit higher moisture regain as compared to CLY fibers (Bredereck and Hermanutz 2005)

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