The role of anionic microparticles in a poly(acrylamide)-montmorillonite flocculation aid system

The hetero-flocculation of wood fibres and fines was investigated for different bridging configurations of poly(acrylamide) and montmorillonite. Montmorillonite platelets are effective bridging agents between adsorbed polymer layers. This was attributed to the high surface charge density, which causes a higher attraction of the cationic polymer segments protruding from the cellulosic surfaces. The polymer therefore strongly attaches to the montmorillonite surface or adopts a more favourable conformation. When polymer is adsorbed on montmorillonite, the resulting bond strength is much weaker due to a flatter conformation caused by the high surface charge. The adsorption sequence of the polymer is therefore crucial to the efficiency of this flocculation aid system. Montmorillonite addition also leads to a stronger bond with ‘depleted’ and ‘transferred’ polymer layers, formed by polymer redistribution between surfaces. This means that the required layer thickness and loop/tail density of the polymer layer for bridging with montmorillonite are lower than for the cellulosic surfaces. Montmorillonite platelets form a strong bridge between adsorbed polymer layers.