Effect of Particle and Salt Concentrations on the Rheological Properties of Cellulose Fibrous Suspensions

Rheological properties of cellulose fibrous suspensions were measured with a cone-plate type rheometer. Effect of particle concentrations, c, and salt concentrations of the systems on the properties were studied. The flow curve of the fully dialyzed system showed Newtonian flow at a particle concentration of 0.1 wt%. However, it showed plateau regions of shear stress over a particle concentration of ca. 0.3 wt%, which is consistent with the critical concentration c0 calculated from the aspect ratio of the fiber particle. The dynamic moduli of the systems were almost independent of angular frequency. They were in proportion to c9/4. The absolute value of zeta potential of the cellulose particle was decreased with increasing salt concentration of the suspension. When the particle concentration was lower than c0, salt concentration had no influence on the flow properties of the system. At higher particle concentration, however, the yield stress was exponentially decreased with decreasing the absolute value of zeta potential of the particle. These facts indicate that the shear stress consists of two different contributions: one is caused by friction of the effective volume of the particles and the other arises from overlapping of the electric double layer of the particles.