Recent Advances in Solvents for the Dissolution, Shaping and Derivatization of Cellulose: Quaternary Ammonium Electrolytes and their Solutions in Water and Molecular Solvents.

Marc Kostag,Thomas Heinze,Kerstin Jedvert,Omar El Seoud,Christian Achtel

doi:10.3390/molecules23030511

Abstract

There is a sustained interest in developing solvents for physically dissolving cellulose, i.e., without covalent bond formation. The use of ionic liquids, ILs, has generated much interest because of their structural versatility that results in efficiency as cellulose solvents. Despite some limitations, imidazole-based ILs have received most of the scientific community’s attention. The objective of the present review is to show the advantages of using quaternary ammonium electrolytes, QAEs, including salts of super bases, as solvents for cellulose dissolution, shaping, and derivatization, and as a result, increase the interest in further investigation of these important solvents. QAEs share with ILs structural versatility; many are liquids at room temperature or are soluble in water and molecular solvents (MSs), in particular dimethyl sulfoxide. In this review we first give a historical background on the use of QAEs in cellulose chemistry, and then discuss the common, relatively simple strategies for their synthesis. We discuss the mechanism of cellulose dissolution by QAEs, neat or as solutions in MSs and water, with emphasis on the relevance to cellulose dissolution efficiency of the charge and structure of the cation and. We then discuss the use of cellulose solutions in these solvents for its derivatization under homogeneous and heterogeneous conditions. The products of interest are cellulose esters and ethers; our emphasis is on the role of solvent and possible side reactions. The final part is concerned with the use of cellulose dopes in these solvents for its shaping as fibers, a field with potential commercial application.

Highlights

The demand for cellulosic fibers—natural and man-made—is increasing continually because of world population growth
Results of DSC, 1 H and 13 C-NMR chemical shifts showed that urea hydrate plays its positive role in dissolution through van der Waals interactions, by accumulating on the hydrophobic face of the AGU to prevent dissolved cellulose chains from re-aggregation [151,152]
The cellulose dissolving power of the aqueous solvent is dependent on Quaternary Ammonium Electrolytes (QAEs) concentration and the corresponding molar ratio water/QAE

Summary

Introduction

The demand for cellulosic fibers—natural and man-made—is increasing continually because of world population growth. A rational strategy to close this “cellulosic fiber gap” is to increase the production of man-made cellulosic fibers, following the principles of green chemistry [1,2,3]. Fibers, e.g., from wood cellulose, are obtained from Viscose (cellulose xanthate in alkali solution) by extrusion in acid bath to produce the fiber Rayon [4,5,6], or by regeneration of cellulose solutions in. N-methylmorpholine N-oxide (NMMO) hydrate in an aqueous bath to produce the fiber Lyocell [7,8,9,10,11]. The limitations of both solvents and processes, coupled with the increased emphasis on Thesustainability limitations ofhave bothprompted solvents and with the increased emphasis on sustainability the processes, search for coupled alternative greener substitutes

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Conclusion