Highly cationic starch and "anionic trash" for optimal filler retention and paper strength?

Cationic starch and anionic sodium polyacrylate (NaPA) were in this work used for flocculation of semi-dilute calcium carbonate dispersions. The polyelectrolytes were added pre-mixed or sequentially to the predominantly cationic calcium carbonate. When used alone, neither of the polyelectrolytes was able to cause a considerable flocculation of the calcium carbonate dispersions. However, when used in combination they enabled a controlled flocculation of the calcium carbonate. The flocculation induced by the polyelectrolyte mixtures was shown to be strongly dependent on the charge density of the starch. Despite the significantly different electrostatic attraction of the oppositely charged NaPA and starch for the predominantly cationic calcium carbonate surface the overall flocculation behaviour was not substantially affected by the sequence of addition of the polyelectrolytes. However, adding starch prior to sodium polyacrylate resulted at most conditions in a somewhat reduced flocculation as compared to when the polyelectrolytes were added pre-mixed or when NaPA was added prior to starch. The flocculation characteristics of the semi-dilute calcium carbonate dispersions induced by the polyelectrolytes were determined by measuring the particle/floc size and the dynamic mobility of the modified solid particles. (C) 2004 Elsevier B.V. All rights reserved.