NMR studies of cellulose dissolution in ionic liquids

This study examines the properties of ionic liquid and co-solvent mixtures, investigating fundamental aspect of cellulose dissolution in ionic liquids and developes a new technique to study the kinetics of cellulose coagulation. The first system that we studied is the mixture of 1-Ethyl-3-Methylimidazolium Acetate (EMIMAc) and Dimethyl Sulfoxide (DMSO). The motivation behind this study is that the use of DMSO as a co-solvent for cellulose dissolution in ionic liquid makes the cellulose processing more efficient and cost effective. Detailed studies of solutions are carried out to probe the macro- and micro-scopic changes of the ionic liquid properties as well as DMSO in the mixtures. The results suggest that ionic liquid and DMSO mixtures behave almost like an ideal solution. Solutions of 1-Butyl-3-Methylimidazolium Chloride (BMIMCl)-cellulose are investigated across a range of cellulose concentrations and temperatures using NMR- spectroscopy and relaxometry, diffusion and viscosity measurements. Using Bloemberg-Purcell-Pound (BPP) theory, NMR relaxation times T1 and T2 have been expressed in terms of an isotropic correlation time, τc for molecular motion. The derivation of the relation between correlation time and translational diffusion shows that the rotational motion can be best correlated to translational motion in term of hydrodynamic radius and activation energy. Mixtures of ionic liquids and carbohydrates (glucose, cellobiose and cellobiose) are investigated using viscosity and NMR spectroscopy, relaxometry and diffusion measurements. The results give the interaction stoichiometry of ionic liquid:hydroxyl group, 1:1. Analysis of the dynamic properties of the mixtures suggests that in solutions the bulk viscosity, η is best replaced by a microviscosity, ηµ = fµη, where fµ is the microviscosity correction factor. A new method to study the kinetics of cellulose coagulation in water from cellulose/IL/co-solvent using NMR has been successfully developed. Diffusion coefficients of EMIMAc and DMSO are found not to be significantly affected by cellulose and DMSO concentrations within the range studied, which suggests that if we want to change the coagulation rate and therefore the morphology, we would need to change the anti-solvent.