Transfer of cationic polyelectrolytes between cellulosic fibres and calcium carbonate particles

The transfer of a high molecular weight cationic polyacrylamide between cellulosic fibres and calcium carbonate particles has been studied in a stirred dispersion. It was found that there is a transfer also at very short times (5 s). The final distribution between fibres and fillers depend on the time the polymer has been adsorbed on the cellulosic fibres before the filler particles are added. If the polymer has been adsorbed a short time on the fibres, it does not have the opportunity to interact with the charges in the porcs of the fibres. The distribution will in this case be given by the outer surface areas of the fibres and fillers respectively since the particles have approximately the same z-potential. If the polymer has been adsorbed a long time it can interact with more charges on the cellulosic fibre. The final distribution of the polymer between fibres and filler particles is for this case approximately determined by the charges available for interaction as given by the adsorption isotherms. The influence of addition level and stirring rate is in line with these arguments. Hydrodynamic forces have a larger effect on larger particles which leads to faster transfer. A higher electrolyte concentration also seems to facilitate transfer. The reason is most likely that the polymers are less tightly bound to the fibres in this case. It has been shown, by adsorbing the polymer on the filler particles, that there is also a transfer of polymer from filler to fibre.