Dissolution of cellulose in mixtures of ionic liquid and molecular solvents: Relevance of solvent-solvent and cellulose-solvent interactions

We have investigated aspects of dissolution of microcrystalline-and fibrous cellulose (MCC, mercerized cotton linters, M-cotton) in binary mixtures of the ionic liquid, IL, 1-allyl-3-methylimidazolium chloride (AlMeImCl), and dipolar aprotic molecular solvents, MS, dimethylsulfoxide (DMSO) and N, N-dimethylacetamide (DMAC). For both celluloses, IL-DMSO was more efficient medium; the maximum cellulose solubility in both IL-MS mixtures occurred at a mole fraction of the IL, chi IL = 0.67. This did not coincide with the maximum observed in the corresponding plot between solution conductivity, lambda and chi IL. As shown by a control experiment using low viscosity model for cellulose, this difference between dissolution and/or conductivity versus chi IL curves is not due to viscosity effect on conductivity. Both curves showed coincidence, however, when values of chi in the absence of biopolymer (due to IL-MS interactions) were subtracted from those in its presence (assigned to both IL-MS and biopolymer binary solvent interactions). The dependence of solution property on solvent mixture composition is traced to the interactions between the biopolymer and solvent components, including hydrogen bonding and hydrophobic interactions. The effects of cellulose dissolution on the morphology and crystallinity of regenerated cellulose were probed by electron microscopy and X-ray diffraction.