Rheology of 1- Butyl-3-Methylimidazolium Chloride Cellulose Solutions

Cellulose is the most common organic polymer on earth. It is a natural, biodegradable polymer that can be obtained from any number of renewable sources. Wood, a major source of cellulose, contains cellulose, lignin, and hemicelluloses. It can be used to make regenerated cellulosic fibers such as rayon whose manufacturing process involves chemicals which are toxic to humans and the environment. Ionic liquids (ILs) are a class of environmentally benign solvents some of which dissolve cellulose.

Cellulose can be dissolved in 1-butyl-3-methylimidazolium chloride ([C₄mim]Cl), an IL. Solutions of [C₄mim]Cl and cellulose with various concentrations were prepared and tested for their rheological characteristics. At high concentrations, low temperatures, and high angular velocities, the IL solutions of cellulose feature a viscoelastic character. Diluted solutions or concentrated ones at low angular velocities behave as viscous liquids.

IL/cellulosic solutions of different degrees of polymerization were prepared and tested for their rheological characteristics. The solutions with lower degrees of polymerization behaved as viscous liquids at all temperatures tested. The solutions with higher degrees of polymerization displayed viscoelastic properties at lower temperatures and the solution with the highest degree of polymerization showed viscoelastic properties at all temperatures tested.

Solutions were prepared manually and mechanically. Mechanically prepared solutions exhibited viscoelastic properties, but one of the manually prepared solutions did not. Limited amounts of lignin and xylose, a typical hemicellulose monomer, were added to some solutions to simulate the composition of wood pulp. These additives increased the complex viscosity of the solutions, and they displayed viscoelastic properties.

The activation energies for shear flow of different solutions were determined from the shift factors with respect to temperature and were higher than those for some polymeric melts. IL cellulose solutions have rheological characteristics similar to some melt blowing grade polypropylene melts or lyocell solutions of comparable concentration, suggesting feasible processing procedures, such as spinning or melt blowing, for the manufacture of fiber or nonwoven products.