Water release from fractionated stock suspension. Part 2. Effects of consistency, flocculants, shear, and order of mixing

Abstract

The rate of gravity drainage from a papermaking stock suspension is highly dependent on the initial consistency of the stock, and on the presence of cellulosic fines. In this study, we fitted the results of testing to a model based on different linear contributions to drainage resistance from fibers and each type of fines. Deviations from the model at relatively high consistency were tentatively attributed to flocculation phenomena. Substantially higher rates of dewatering were achieved by selectively treating the fines, the fibers, or the combined furnish with cationic polyelectrolytes. Results were consistent with several mechanisms, which might act in parallel during ordinary papermaking. Attachment of cellulosic fines to fiber surfaces can prevent those fines from migrating to choke points within a wet web. Agglomeration of fines to each other can reduce their effective surface area. Flocculation of the fibers can make the fiber mat less uniform, thus providing larger channels for water to flow from the mat.