EFFECT OF PULPING CONDITIONS AND BLACK LIQUOR COMPOSITION ON NEWTONIAN VISCOSITY OF HIGH SOLIDS KRAFT BLACK LIQUORS

The influence of black liquor composition and solids concentrations on the Newtonian viscosity of slash pine black liquors over wide ranges of temperature (up to 140 degrees C) and solids concentrations (betwee n 50% and 83% solids) has been studied. It was found that the zero she ar rate viscosity of high solids black liquors depends strongly on the cooking conditions and/or black liquor composition. Not only is high solids viscosity affected by lignin molecular weight and lignin concen tration in the liquor but other organic and inorganic constituents of black liquor also make a significant contribution to viscosity. The de pendency of zero shear rate viscosity on solids concentrations, and te mperature is defined. The Newtonian viscosities vary over a wide range depending on temperature, solids concentrations and solids compositio n. The results indicate that, at fixed levels of effective alkali and sulfidity, the zero shear rate viscosities can be described as a funct ion of both Lignin concentration and lignin molecular weight. The visc osity of black liquor is an increasing function of the organics-to-ino rganics ratio and is a decreasing function of the concentration of sod ium and chloride ions and pH of the liquor.