Influence of water on cellulose-EMIMAc solution properties: a viscometric study

The influence of water on cellulose dissolved in 1-ethyl-3-methylimidazolium acetate (EMIMAc) is analysed by measuring steady state viscosity of dilute solutions. The goal is to determine: (a) the maximal water content allowing keeping cellulose dissolved (in dilute regime) and (b) the influence of water on solution flow and cellulose hydrodynamic properties. Mixing EMIMAc and water is exothermal and EMIMAc-water viscosity does not obey a logarithmic mixing rule suggesting strong interactions between the components. Newtonian flow of cellulose-EMIMAc-water solutions was recorded at water concentrations below 15 wt% and a shear thinning was observed for higher water content. It was suggested that above 15 wt% water cellulose is not completely dissolved: swollen aggregates form a sort of a suspension which is structuring under shear. Cellulose intrinsic viscosity showed a peak at 10 wt% water-90 wt% EMIMAc. It was hypothesised that the addition of water leads to the formation of large cellulose aggregates due to the preferential cellulose-cellulose interactions.