Mini-Encyclopedia of Papermaking Wet-End
Part Two: Definitions and Concepts
The site-blocking model has been used to account for the beneficial effect of certain pretreatment conditions on the action of flocculating chemicals and microparticle treatment programs. In principle there are two ways in which a highly charged cationic polymer can improve the flocculating ability of a very-high-mass cationic flocculant. On the one hand, it might help to neutralize excess anionic colloidal charges in the system that otherwise would have neutralized the charges on the flocculant. On the other hand, it can partly cover the surfaces, blocking many potential bonding sites. The high-mass cationic flocculant still may be able to find sufficient anionic sites on the furnish surfaces to become attached. However, the presence of the lower-mass cationic additive prevents the long chains from lying down. Instead, long loops and tails of polymer are expected to extend into the solution.
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