The use of oppositely charged polyelectrolytes as flocculants and retention aids

New results for flocculation of cellulose-clay mixtures with a so-called dual system, consisting of the polycation poly(dimethyldiallylammonium chloride), PDMDAAC, and different polyanions are presented. The flocculation behaviour was investigated by different procedures: polyelectrolyte titration, dewatering test, and measuring the residual turbidity. It should be pointed out that the flocculation mechanism depends on the molecular weight of the polyanion used. In the first case, when the molecular weight of the polyanionic compound is relatively low, the complexation between the polycation and the polyanion is said to be the mechanism and the ratio of anionic to cationic charges (n(-):n(+)) is of crucial importance. Using a very high molecular weight polyanion (much greater than 1 million) as one component of the dual system, the mechanism of reaction consists of bridging and patch effects.