FLOCCULATION OF CATIONIC AMYLOPECTIN STARCH AND COLLOIDAL SILICIC-ACID - THE EFFECT OF VARIOUS KINDS OF SALT

The kinetics of the flocculation of nanosized silica particles (5 nm) with cationic amylopectin has been investigated with stopped-flow tech nique. The flocculation process has been followed with turbidity. A ki netic mechanism is suggested where the initial process is a bridging f locculation. In this process the large amylopectin,molecules gather a number of the small silica particles forming a polyelectrolyte complex . This process is followed by a collapse of the formed flocs. These pr ocesses have time constants of less than 1 s. In a subsequent process the polyelectrolyte complex may also flocculate on a larger time scale , several seconds. The effect of mono- and divalent ions on the floccu lation processes has been investigated. A large effect was found when a monovalent cation was replaced by a divalent cation indicating that the electrostatic screening of the silica particles is the most import ant factor. (C) 1998 Elsevier Science B.V. All rights reserved.