Assessing cellulose dissolution efficiency in solvent systems based on a robust experimental quantification protocol and enthalpy data

Dissolution of microcrystalline cellulose (MCC) in pure ionic liquids (ILs) and IL/dimethyl sulfoxide (DMSO) mixtures (mole fraction chi(DMSO) =0.2-0.9) was quantified using a specially constructed mechanical stirring system that allows reproducible agitation speed; temperature control, and minimum solution-air contact. The electrolytes employed were: 1-(n-butyl)-3-methylimidazolium acetate (C(4)MeIm AcO), 1-(methoxyethyl)-3-methylimidazolium acetate (C(3)OMeIm AcO), 1,8-diazabicyclo{[}5.4.0] undec-7-enium acetate (DBU AcO), tetramethylguanidinium acetate (TMG AcO), and tetra(n-butyl)ammonium fluoride hydrate (TBAF center dot xH(2)O). The effects on MCC dissolution of IL/DMSO composition, and temperature (50, 70 degrees C) were studied. C(4)MeIm AcO and C(4)MeIm AcO/DMSO were more efficient solvents than their C(3)OMeIm AcO counterparts, due to ``deactivation{''} of the ether oxygen of C(3)OMeIm AcO. MCC dissolution by C(4)MeIm AcO/DMSO was compared with DBU AcO/DMSO, TMG AcO/DMSO at chi(DMSO) =0.6, and TBAF center dot xH(2)O/DMSO at chi(DMSO) = 095. The relative efficiency was (solutions in DMSO): C(4)MeIm AcO > C(3)OMeIm AcO > DBU AcO > TMG AcO > TBAF center dot xH(2)O. The efficiency of C(4)MeIm AcO relative to C(3)OMeIm AcO is due to higher solution basicity. Isothermal titration calorimetry was used to study cellobiose-solvent interactions. Except for TBAF center dot xH(2)O/DMSO, these interactions are exothermic; the relative solvent efficiency increases with increasing dissolution vertical bar enthalpy vertical bar. Using the mole fraction concentration scale to report cellulose dissolution avoids possible ambiguities. (AU)