The flocculation mechanism of microparticulate retention aid systems

We have investigated the kinetics of fines deposition on pulp fibres with a cationic poly(acrylamide) (CPAM)/bentonite (montmorillonite) retention aid. Different CPAM/montmorillonite bridging configurations between fibres and fines were studied and compared with single polymer layers. The results show that montinorillonite platelets increase the bond strength of adsorbed polymer layers on fibres and fines, and reduce the polymer transfer between surfaces. Moreover, montinorillonite platelets are effective bridging agents between "inactive" polymer layers. The mechanism of these flocculants is explained in terms of surface charge densities and polymer layer-conformations. These results provide indications for the optimization of these systems in mill conditions.