Polymer transfer during fines detachment under turbulent flow: Mechanism and implications

The transfer of polymer between papermaking surfaces was characterized for several commercial retention aids. Polymer transfer during particle detachm ent stabilizes the suspension, and lean's to impaired polymer layers. A kin etic model, describing simultaneous particle deposition and polymer transfe r was developed and validated. In the experiments, the fines deposition on polymer-coated fibres was followed. The effect of polymer chemistry salt co ncentration and shear rate on the kinetic parameters was investigated Two m ain kinetic regimes can be distinguished, corresponding to flocculation mec hanisms by charge reversal and bridging. Bridging polymers generate stronge r bonds, but are more easily transferred On the other hand, highly charged polymers, inducing aggregation by charge reversal or neutralization, produc e weaker bonds but undergo less transfer The observed kinetic constants wer e extrapolated to papermaking shear rates. Even with conservative estimates , fines are quickly and permanently detached in the presence of high shear: These results could explain? the observed loss in retention on high-speed papermachines.