Dynamics of polymer-induced hetero-flocculation of wood fibres and fines

The kinetics of polymer-induced hetero-flocculation of wood fibres and fines was investigated. A polymer layer (cationic poly(acrylamide)) was deposited on either the fibres or the fines, and the fines concentration was followed after mixing both components. It is shown that the flocculation state is only transient. This is explained by a redistribution of polymer between surfaces upon particle detachment, which leads to a re-stabilisation of the system. Simultaneous particle deposition, particle detachment and polymer transfer determine the apparent particle detachment rate. The detachment rate is strongly shear-dependent, and the resulting polymer layers after redistribution have a reduced bridging ability compared to the fresh layers.