Insight into the Cosolvent Effect of Cellulose Dissolution in Imidazolium-Based Ionic Liquid Systems

Abstract

Recently, it has been reported that addition of a cosolvent significantly influences solubility of cellulose in ionic liquids (ILs), but little is known about the influence mechanism of the cosolvent on the molecular level. In this work, four kinds of typical molecular solvents (dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), CH₃OH, and H₂O) were used to investigate the effect of cosolvents on cellulose dissolution in [C₄mim][CH₃COO] by molecular dynamics simulations and quantum chemistry calculations. It was found that dissolution of cellulose in IL/cosolvent systems is mainly determined by the hydrogen bond interactions between [CH₃COO](-) anions and the hydroxyl protons of cellulose. The effect of cosolvents on the solubility of cellulose is indirectly achieved by influencing such hydrogen bond interactions. The strong preferential solvation of [CH₃COO](-) by the protic solvents (CH₃OH and H₂O) can compete with the cellulose-[CH₃COO](-) interaction in the dissolution process, resulting in decreased cellulose solubility. On the other hand, the aprotic solvents (DMSO and DMF) can partially break down the ionic association of [C₄mim][CH₃COO] by solvation of the cation and anion, but no preferential solvation was observed. The dissociated [CH₃COO](-) would readily interact with cellulose to improve the dissolution of cellulose. Furthermore, the effect of the aprotic solvent-to-IL molar ratio on the dissolution of cellulose in [C₄mim][CH₃COO]/DMSO systems was investigated, and a possible mechanism is proposed. These simulation results provide insight into how a cosolvent affects the dissolution of cellulose in ILs and may motivate further experimental studies in related fields.

Efficiency of hydrophobic phosphonium ionic liquids and DMSO as recyclable cellulose dissolution and regeneration media

“…However, from our and other past studies, 40,58 it is apparent that there is a clear "co-solvent" effect on the dissolution of cellulose, even upon imidazolium ionic liquids like [emim] [OAc]. Although it dissolves cellulose to a high degree, the amount of cellulose able to be dissolved with the addition of DMSO is dramatically increased when compared to the neat ionic liquid, up to 0.79 mol AGU : IL, or 1.7 mol IL : AGUsuggesting that not every hydroxyl is being bound by one anion.…”

“…40 The most posited mechanism of action of this "co-solvent effect" is the strong ability of the highly dipolar DMSO (or other dipolar aprotic solvent) to solvate both the cation and anion, increasing ion pair separation and thus 'freeing' the hydrogen-bond basic anion to bond to cellulose hydroxyl groups. 35,36,56,58 The role of preferential solvation is debated, with Xu et al suggesting the preferential solvation of the cation plays an important part in the co-solvent effect in the [bmim][OAc]/DMSO solvent system.…”

The Properties of Choline Chloride-based Deep Eutectic Solvents and their Performance in the Dissolution of Cellulose

“…Co-solvents can improve solubility by reducing the hydrophobicity of cellulose or enhancing the reactive activity of solvents (Gericke et al 2012;Zhao et al 2013). Three classes of co-solvents, including aprotic co-solvents, QASs, and PEG (Supplementary Material Fig.…”

Gelation and decrystallization of cellulose by TAAHs/DMSO treatment and the role of anions and cations

“…Recently, ionic liquids (ILs) have been reported as solvents for dissolution of cellulose with advantages of a superior dissolution capability, easy recyclability, a non-detectable vapor pressure, and thermal stability (Lv et al 2012;Zhao et al 2012a). However, despite these benefits, industrial processes using ILs are limited by drawbacks of hazardous toxicity, high price, slow dissolution rate, high solution viscosity, and high dissolution temperature (Petkovic et al 2010;Rinaldi 2011;Zhang et al 2012;Xu et al 2013;Zhao et al 2013;Luo et al 2014). To overcome these problems, addition of dipolar aprotic solvents, including dimethyl sulfoxide (DMSO), to ILs has been used (Gericke et al 2011;Rinaldi 2011;Xu et al 2013;Andanson et al 2014).…”

“…The effect of the fluoride ion on dissolution of cellulose is interesting, even though there are few studies regarding the effect of the fluoride ion on ILs (Vitz et al 2009;Pinkert et al 2010). Moreover, the solvent DMSO improves ionic dissociation of TAAH and transport of ions in cellulose molecules (Huo et al 2013;Zhao et al 2013;Andanson et al 2014). TAAHs/DMSO has advantages over pure ILs.…”