Cellulose in Ionic Liquids and Alkaline Solutions: Advances in the Mechanisms of Biopolymer Dissolution and Regeneration

Abstract

This review is focused on assessment of solvents for cellulose dissolution and the mechanism of regeneration of the dissolved biopolymer. The solvents of interest are imidazole-based ionic liquids, quaternary ammonium electrolytes, salts of super-bases, and their binary mixtures with molecular solvents. We briefly discuss the mechanism of cellulose dissolution and address the strategies for assessing solvent efficiency, as inferred from its physico-chemical properties. In addition to the favorable effect of lower cellulose solution rheology, microscopic solvent/solution properties, including empirical polarity, Lewis acidity, Lewis basicity, and dipolarity/polarizability are determinants of cellulose dissolution. We discuss how these microscopic properties are calculated from the UV-Vis spectra of solvatochromic probes, and their use to explain the observed solvent efficiency order. We dwell briefly on use of other techniques, in particular NMR and theoretical calculations for the same purpose. Once dissolved, cellulose is either regenerated in different physical shapes, or derivatized under homogeneous conditions. We discuss the mechanism of, and the steps involved in cellulose regeneration, via formation of mini-sheets, association into "mini-crystals", and convergence into larger crystalline and amorphous regions. We discuss the use of different techniques, including FTIR, X-ray diffraction, and theoretical calculations to probe the forces involved in cellulose regeneration.

2D HSQC Chemical Shifts of Impurities from Biomass Pretreatment

“…For instance, for 1‐butyl‐3‐methylimidazolium acetate the chemical shift of the C 6 carbon occurred at δ H /δ C 1.73/31.3 in both samples. This also agrees with El Seoud et al., who reported stronger changes in chemical shifts of C 2 due to the increased hydrogen bonding with the cellobiose …”

“…El Seoud et al. also reported that the chemical shift of an ionic liquid containing an acetate anion [1‐( n ‐butyl)imizaolium acetate] was influenced by the presence of cellobiose . Further, the C 2 of 1‐butyl‐3‐methylimidazolium acetate had a chemical shift at δ H /δ C 10.43/138.0, but when combined with the pretreated biomass the chemical shift was located at δ H /δ C 10.21/137.8, a difference of δ H /δ C 0.22/0.2.…”

Vapor Phosphorylation of Cellulose by Phosphorus Trichlo-Ride: Selective Phosphorylation of 6-Hydroxyl Function—The Synthesis of New Antimicrobial Cellulose 6-Phosphate(III)-Copper Complexes

“…We assumed that ionic liquid based solvents that were applied for the dissolution of cellulose [ 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 ] can also be applied for the dissolution of cellulose- O -phosphates.…”

Cellulose Dissolution in Mixtures of Ionic Liquids and Dimethyl Sulfoxide: A Quantitative Assessment of the Relative Importance of Temperature and Composition of the Binary Solvent

“…In the present case, therefore, WB is much more sensitive to changes in the experimental variables than other solvatochromic probes that are used to calculate specific Cel-solvent interactions. Note that empirical solvent polarity is related to the parameters that describe the specific solute–solvent interactions by Equation (5) [ 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 ]: E T (probe) = E T (probe) 0 + a SA + b SB + d SD + p SP where SB is as defined before; SA , SD , and SP refer to Lewis acidity, dipolarity, and polarizability, respectively. That is, the dependence of E T (probe) on the experimental variables reflects collectively the dependence (on the same variables) of hydrogen bonding (as given by SA and SB ) and the hydrophobic interactions (related to SP ).…”