CHARACTERIZATION OF WET POWDER MASSES WITH A MIXER TORQUE RHEOMETER .3. NONLINEAR EFFECTS OF SHAFT SPEED AND SAMPLE WEIGHT

We used mixer torque rheometry to examine the effects of shaft speed and sample weight on the theological behavior of a model wet mass consisting of microcrystalline cellulose and water. Both variables contribute differently to the measured parameters of mean torque and torque range (amplitude). For small weights, the effect of shaft speed is small, but for large weights, shaft speed has a greater effect. For large sample weights, the effect of shaft speed on measured mean torque can be modeled by the Herschel-Buckley model originally developed for concentrated dispersions, enabling yield stresses and viscosities to be calculated. The data generated compare favorably with those measured previously by capillary rheometry.