Determination of intrinsic viscosity of native cellulose solutions in ionic liquids

The weight-average molecular weights of six native cellulose samples in ionic liquids were determined through steady shear viscosity measurements in the ionic liquid butyl methyl imidazolium chloride. The intrinsic viscosity [η] in ethyl methyl imidazolium acetate (EMImAc) is measured using a gravity-driven glass capillary viscometer and found to be independent of temperature in the range of 30-80 °C, disproving a literature report of [η] in EMImAc, exhibiting a strong temperature dependence. Findings are contrasted with values of intrinsic viscosity in cupriethylenediamine hydroxide, the most widely used solvent to dissolve and analyze the molecular weight of cellulose pulps in industry. Differences are tentatively attributed to the different temporary association properties of cellulose chains in the two solvents. Finally, it is demonstrated that cellulose adsorbs at the air/solution interface in three different ionic liquids to create a viscoelastic liquid interfacial layer of higher concentration. Adsorption at the air/solution interface gives an extra contribution to the measured torque in various rotational rheometer geometries, which apparently simply adds to the torque from the pure bulk solution.