Effect of Carboxymethylcellulose on Agglomeration and Dispersal of Polystyrene Particle Agglomerates with Step-Wise Shear Rate Change

Dispersion and agglomeration of particles with a drastic change in fluid flow differs from those under a steady shear flow. In this study, the development and destruction of particle agglomerates with step-wise shear rate change were investigated by microscopic observation, and the results were compared with particle dispersibility predicted from rheological data. Polystyrene particles with strong agglomerative properties could be controlled by addition of small amount of carboxymethylcellulose (CMC). Once the particles were sufficiently dispersed, the agglomeration process was dominated by the collision of particles and was not affected by polymer concentration. When the amount of adsorbed CMC was sufficient to prevent the aggregation of particles, agglomerates readily dispersed to an agglomerative state corresponding to the applied shear rate. However, insufficient adsorption of CMC resulted in a heterogeneous agglomeration process that took longer time to attain steady agglomerated state. Slurry viscosity was employed to evaluate agglomerative nature except under conditions of complete dispersion.