Direct sulfation of cellulose fibers using a reactive deep eutectic solvent to produce highly charged cellulose nanofibers

Juho Antti Sirviö,Henrikki Liimatainen,Jonne Ukkola

doi:10.1007/s10570-019-02257-8

Juho Antti Sirviö, Henrikki Liimatainen + Show 1 more

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https://doi.org/10.1007/s10570-019-02257-8

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Journal: Cellulose	Publication Date: Jan 14, 2019
Citations: 123	License type: open-access

Affiliation: University of Oulu

Abstract

Wood cellulose pulp was sulfated using a reactive deep eutectic solvent (DES). DES was prepared by heating sulfamic acid and urea together at 80 °C at a molar ratio of 1:4, 1:3, or 1:2. Sulfation of cellulose was performed by mixing dry cellulose fibers with DES at 80 °C, followed by heating at 150 °C for half an hour. Anionic charge as high as 3 mmol/g (degree of substitution of 0.68) was obtained with this simple chemical modification of cellulose at an elevated temperature using DES both as reaction media and reagent without any external solvent. The decrease in the urea content of DES improved the sulfation efficiency. In addition, the presence of urea led to the carbamation of cellulose to some extent. Cellulose sulfate (charge of 2.40 mmol/g) became a gel-like material in water, and after passing once through a microfluidizator, a highly transparent nanocellulose gel (transmittance of 0.1% solution at a visible light range was over 95%) was obtained. Sulfated cellulose nanofibers (SCNFs) exhibited a width of around 4 nm with a minor presence of elemental fibril aggregates (containing five or less elemental fibrils). SCNFs with high aspect ratio can have a potential end-use as a rheology modifier because of their high viscosity even at low concentrations or act as reinforcing additives.Graphical abstract

Highlights

In the field of sustainable material and chemical production, the isolation of nano-sized cellulose fibers from natural cellulose fibers has gained significant scientific and industrial interest in recent years (Charreau et al 2013; Kim et al 2015)
Reactive deep eutectic solvent (DES) based on sulfamic acid and urea was found to be an efficient sulfating agent for cellulose fibers
A significantly high sulfate group content could be achieved using DES in external solvent-free conditions using a modest excess of sulfating chemical compared with cellulose

Summary

Introduction

In the field of sustainable material and chemical production, the isolation of nano-sized cellulose fibers from natural cellulose fibers has gained significant scientific and industrial interest in recent years (Charreau et al 2013; Kim et al 2015). The chemical modification of natural cellulose fibers prior to the liberation of CNFs can improve the quality of nanocellulose (e.g. more homogeneous size distribution) and lead to upgraded properties, such as ion exchange capability. The chemical pre-treatment can significantly decrease the energy consumption of nanocellulose production (Klemm et al 2011). Most often these pretreatments are based on the introduction of carboxylic acid groups into cellulose by carboxymethylation (Wagberg et al 2008; Naderi et al 2014) or by using (2,2,6,6-tetramethyl-piperidin-1-yl)oxyl (TEMPO) (Saito et al 2006; Fukuzumi et al 2009) or sequential periodate-chloride oxidations (Liimatainen et al 2012; Tejado et al 2012)

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