Optimization of Flocculation and Drainage for Microparticle Systems by Seta Potential Control, 1996 Papermakers Conference Proceedings

A laboratory system was developed to simultaneously measure the zeta-potential, flocculation, and drainage of pulp and filler suspensions, subjected to hydrodynamic shear flows. With this instrument, flocculation and drainage were optimized for single polymer systems and microparticle systems. For wood free grade pulp, charge neutralization did not affect flocculation nor drainage by itself, but it enhanced the effectiveness of polymers. In single polymer systems, anionic polyacrylamide (PAM), when the zeta potential had been properly controlled, made flocs but decreased drainage. Cationic PAM improved flocculation to a large extent, but drainage improvement was little and almost negligible. In microparticle systems, sequential addition of poly-DADMAC, bentonite, and anionic PAM made large flocs but decreased drainage. Combination of poly-DADMAC, cationic PAM, and bentonite greatly improved both flocculation and drainage. For wood containing grade, charge neutralization increased drainage by itself. Flocculation did not occur by charge neutralization alone. Poly-DADMAC, bentonite, and anionic PAM increased both flocculation and drainage. Reversing the order of bentonite and anionic PAM, a microparticle system of poly-DADMAC, anionic PAM, and bentonite further increased flocculation and drainage. Drainage increases by bentonite addition were strongly influenced by charge neutralization and thus the zeta potential should be properly controlled in microparticle systems.