Mini-Encyclopedia of Papermaking Wet-End Chemistry
Part Two: Definitions and Concepts

Reversibility of Flocculation

The term "reversibility of flocculation" refers to fibrous slurries that have been treated with a flocculating chemical and then dispersed by hydrodynamic shear. It has been observed that different chemical systems respond differently in this kind of situation. In general, very high molecular mass flocculants tend to behave irreversibly, meaning that the dispersed flocs do not form again to the same degree. By contrast, slurries that have been flocculated by highly charged polymers tend to behave reversibly. Not only to the fiber flocs form again, but also the levels of fines retention and drainage rates in jar tests tend to be independent of shear history. There is evidence that microparticle retention aid systems are partly reversible, and this might help explain how they perform on paper machines. In principle, the papermakers would like to have fibers remain well dispersed under conditions of shear in the approach system, but become attracted to each other for efficient retention aid drainage when on the forming fabric.

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