We studied the dissolution of microcrystalline cellulose (MCC) in mixtures of DMSO with 19 ionic liquids (ILs), at a fixed temperature (70 °C) and mole fraction of DMSO (cDMSO = 0.6). In order to access quantitatively the relative importance of cellulose-solvent interactions to biopolymer dissolution we correlated the mass fraction (MCC-m%) and mole fraction (MCC-c) of dissolved cellulose with the physicochemical properties of these mixtures. The solvent descriptors that gave the best correlations are Lewis acidity, Lewis basicity, the molar volume of the IL, and the Lorentz-Lorenz refractive index function of the solvent binary mixture. The multi-parameter correlations quantify, for the first time, the relative importance of cellulose-solvent interactions. Namely, an efficient cellulose solvent should disrupt the inter- and intramolecular hydrogen bonding, and the hydrophobic interactions present in the biopolymer. Using chemometrics, we derived equations that quantify the dependence of MCC-m% (or MCC-c) on T = 40, 60, 80 °C, and cDMSO = 0.4, 0.6, and 0.8. Cellulose dissolution increases as a function of increasing both variables; contribution of cDMSO is larger than T in some cases. Solvent empirical polarity is qualitatively employed to rationalize cellulose dissolution. Using the solvatochromic probe 2,6-dichloro-4-(2,4,6-triphenylpyridinium-1-yl)phenolate (WB), we calculated the empirical polarity ET(WB) of cellobiose (a model for MCC)/IL-DMSO. ET(WB) correlates perfectly with T (fixed cDMSO) and with cDMSO (fixed T). Thus, there is ground for using ET(probe) to assess cellulose dissolution efficiency. We calculated values of MCC-m% under conditions other than those employed to generate the statistical model, and determined the corresponding MCC-m% experimentally. The excellent agreement between both values shows the robustness of the statistical model, and the usefulness of our approach to predict cellulose dissolution, thus saving time, labor, and material

Understanding cellulose dissolution in mixtures of DMSO and ionic liquids (ILs): Quantifying the relative importance of the IL molecular structure, binary solvent composition, and the temperature

ACS Spring Meeting 2021

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