From cellulose fibrils to single chains: understanding cellulose dissolution in ionic liquids

Abstract

Cellulose is the most abundant and renewable organic compound on Earth, it is however not soluble in common organic solvents and aqueous solutions. Cellulose dissolution is a key aspect to promote its value-added applications. Ionic liquids (ILs) have been shown to solubilize cellulose under relatively mild conditions. The easy processability of cellulose with ILs and their environmental-friendly nature prompted research in various fields such as biomass pretreatment and conversion, cellulose fiber and composite production, and chemical conversion of cellulose in ILs. Progress has been made on understanding the mechanism of cellulose dissolution in ILs, including the structural characteristics of ILs that are cellulose solvents, however many details remain unknown. In light of rapid development and importance of cellulose dissolution in the field of IL-based cellulose and biomass processing, it is necessary to provide an overview of current understanding of cellulose dissolution in ILs and outline possible future research trends. Recent literature studies suggest that synergistic effects between the anions and the cations of ILs need to be revealed, which requires refining the structure of cellulose elementary fibrils, simulation of more realistic cellulose fibrils and detailed studies on the solution structure of cellulose in ILs. After analyzing literature studies, three interacting modules are identified, which are crucial to understand the process of cellulose dissolution in ILs: (1) the structure of elementary fibrils; (2) solvation of cellulose in ILs; and (3) solution structure of cellulose solubilized in ILs. A coherent analysis of these modules will aid in better design of more efficient ILs and processes.

Cellulose–solvent interactions from self-diffusion NMR

“…The difference is consistent with the expected scaling R h $ M l , where l & 0.55 for polymer chains in good solvents (De Gennes 1979, Sung andChang 1993). Moreover these values are in agreement with other reported in literature for other solvents (Saalwächter et al 2000;Yuan and Cheng 2015).…”

Ionic Liquid as Reaction Media for the Production of Cellulose-Derived Polymers from Cellulosic Biomass

“…A number of works, including several reviews [76][77][78][79][80][81][82], have been already published on the cellulose dissolution process in ILs. Thus, this subject will not be discussed in depth in this review.…”

Functional nanomaterials through esterification of cellulose: a review of chemistry and application

“…These hydrogen bonds give rise to various three-dimensional (3D) arrangements of the cellulose chains, leading to coexisting of crystalline and amorphous regions within cellulose fibers (John and Thomas 2008;Klemm et al 2005;Moon et al 2011;Nada and Hassan 2003). To be more specific in the case of cellulose from plant sources, approximately 36 cellulose chains arrange as a basic fibrillar unit known as elementary fibrils, which have a characteristic lateral dimension of 1.5-3.5 nm with the length up to 100 nm (Chinga-Carrasco 2011; Klemm et al 2005;Krassig 1990;Yuan and Cheng 2015). These elementary fibrils are further assembled as microfibrils with widths in the range of 10-30 nm, which in turn further assemble into the familiar cellulose macrofibers.…”