Flocculation in suspensions of microcrystalline cellulose by microparticle retention aid systems

Flocculation in suspensions of microcrystalline cellulose by microparticle retention aid systems was investigated. Cationic polyacrylamides of different degrees of substitution were used in combination with anionic colloidal silica or anionic montmorillonite clay. For comparison, we also studied flocculation by cationic polyacrylamides, and cationic potato starch as single-component systems and by the two-component polymer system polyethyleneimine and anionic polyacrylamide. The flocculation experiments were carried out under turbulent conditions in a Britt jar and the extent of reflocculation after high-shear deflocculation was evaluated by alternating the propeller speed. The degree of reflocculation was defined as the ratio of two measurements of floc size, taken at low shear, but separated by an intervening period at high shear. The degree of reflocculation was high in all systems, including single polymeric systems. In two-component systems, the extent of reflocculation depends on the amounts of added flocculants, and the reflocculating effect of the second component is high even after prolonged shearing of the suspension before the second addition. Sites for interaction with the second component are obviously available when flocs are broken even after long shearing.