Investigations of the Flocculation Behavior of Microparticle Retention Systems, 2001 Papermakers Conference Proceedings

For some two decades microparticle retention systems, consisting of a cationic polymer and anionic particles, have been applied to the papermaking process successfully. In spite of the multitude of studies that have gone into the subject, there is still some controversy about the underlying mechanisms and processes.

The focus of this presentation is on investigations of the flocculation behavior of microparticle retention systems in different furnishes. The state of flocculation in the paper furnish was characterized by two different methods: the first one being image analysis, the second one being the scattering of laser light. Both methods and their application to floc measurement in flowing furnish will be described briefly. The combination of these two methods leads to a more elaborate view of the flocculation mechanism, as the methods generate complimentary information.

Irrespective of the kind of microparticle system, it was found that the dosage of cationic polymer influences the floc size strongly. On the other hand the dosage of the microparticle component has an impact on the floc size only in the case of the cationic polyacrylamide (CPAM)- bentonite system. The floc index, measured by light scattering, is affected in both cases by the dosage of polymer and microparticle component. This is explained by resulting differences in the floc density. The effect of charge balance and zeta-potential on floc index is discussed. Another important parameter is the kinetics of flocculation. The addition of CPAM only results in a very fast formation of flocs whereas microparticle components are reducing the flocculation rate. Finally, it was possible to show a good correlation between floc index and filler retention during hand sheet forming.