STEADY SHEAR-FLOW PROPERTIES OF HIGH SOLIDS SOFTWOOD KRAFT BLACK LIQUORS - EFFECTS OF TEMPERATURE, SOLIDS CONCENTRATIONS, LIGNIN MOLECULAR-WEIGHT AND SHEAR RATE

The steady shear flow properties of several softwood kraft black liquo rs (slash pine) from a two level, four variable factorially designed p ulping experiment were determined for solids concentrations from 50% t o 85%, temperatures from 40 degrees C to 140 degrees C and shear rates up to 10,000, s(-1) by using Instron capillary and Haake coaxial cyli nder rheometers. It was shown that the slip velocity at the wall of th e capillary is insignificant and that a two capillary method can be us ed to determine the viscosity of the samples. At high solids, black li quor can exhibit non-Newtonian behavior dependent upon temperature, so lids concentrations, solids composition and shear rate. In general, th e liquors behave as pseudoplastic fluids. The exact level of viscosity at any given condition is dependent upon the solids composition which will vary from liquor-to-liquor. The flow behavior of the liquors was described using power-law, Cross and Carreau-Yasuda models. Superposi tion principles developed for polymer melts and concentrated polymer s olutions were applied to obtain reduced correlations for viscosity beh avior of the liquors. By using a suitable reference temperature, relat ed to the glass transition temperature of black liquors, a generalized WLF type shift factor was obtained for the liquors used in this study and can be used to obtain a reduced plot of viscosity behavior of oth er black liquors.