Specific ion effects in the adsorption of carboxymethyl cellulose on cellulose: The influence of industrially relevant divalent cations

Vishnu Arumughan,Harald Brelid,Sverker Albertsson,Anette Larsson,Tiina Nypelö,Merima Hasani,Lars Wågberg

doi:10.1016/j.colsurfa.2021.127006

Abstract

The adsorption of carboxymethylcellulose (CMC) on cellulose surfaces is of relevance from both academic and industrial perspectives as it facilitates resource-efficient modification of cellulose fibres that allows them to carry negative charges. It is known that, compared to monovalent ions, Ca2+ ions are superior ions in facilitating CMC adsorption and the subsequent introduction of charge on cellulose fibres. However, the formation and deposition of calcium oxide involved in this process necessitates the search for alternative cations. Magnesium ions form one of the more promising candidates since they are already used in the pulping process to prevent cellulose degradation during peroxide bleaching. This work aims at elucidating the effects of the industrially relevant alkaline earth metal divalent cations Mg2+ and Ca2+ on the CMC adsorption process onto cellulose surfaces. Quartz Crystal Microbalance (QCM-D) technology was used to follow the adsorption in model systems in real time, whereas the adsorption of CMC on commercial fibres was studied using polyelectrolyte titrations, total organic carbon (TOC) analysis and conductometric titrations. This study shows that the presence of Ca2+ ions was more favourable for the adsorption of CMC to both types of cellulosic surfaces than Mg2+ ions. The distinction in the adsorption behaviour in the presence of Mg2+ and Ca2+ is suggested to be due to the differences in the polarizability of the ions. The findings are decisive in designing efficient industrial processes for the adsorption of polyelectrolytes to cellulose surfaces of similar charge.

Highlights

The application of polyelectrolyte adsorption and Layer-by-Layer assembly at a solid-liquid interface is a flexible and versatile approach for surface modifications [16]
The AFM height profiles obtained for the nanofibrillated cellulosecoated quartz crystal microbalance with dissipation monitoring (QCM-D) sensor (Fig. 1a) reveal the fibrillar features
Our findings indicate that the presence of Ca2+ enhances carboxymethyl cellulose (CMC) adsorption, thereby implying that interactions between CMC chains and the cellulose fibre surface are stronger

Summary

Introduction

The application of polyelectrolyte adsorption and Layer-by-Layer assembly at a solid-liquid interface is a flexible and versatile approach for surface modifications [16]. Cellulose-rich materials have been functionalized by cationic and anionic polyelectrolyte adsorption and, by the wise selection of polymers and other functional entities, it is possible to create interactive and reactive surface layers [42]. The interaction of cationic polyelectrolyte with negatively charged cellulose surface is attractive and is already utilized in the paper industry to improve the physical properties of paper products. CMC is a negatively-charged water-soluble polyelectrolyte derived from cellulose [12,18,37]. It has a wide range of applications in pharmaceutical products, foods, mineral processing, paper making etc [27,28,45]. In mineral processing and paper making adsorption of CMCs on surfaces are important

Objectives

Methods

Results

Discussion

Conclusion