Heteroflocculation of kaolin pre-treated with oppositely charged polyelectrolytes

Heteroflocculation studies of kaolin particles have been carried out by mix ing two kaolin suspensions; one stabilised by a cationic polymer and the ot her stabilised by a highly charged and low molecular weight anionic polymer . Molar mass and charge density of cationic polymer as well as the mixing r atio of oppositely charged suspensions were varied. Flee size and degradati on during shearing were investigated by measuring hoc size using a light sc attering/diffraction method at different flow rates. It was observed that f loc size was small when subjected to a low flow rate and decreased with inc reasing how rate. Cationic polymers with high molar mass and low charge den sity produced flocs with high resistance towards flee degradation. Maximum flee size was obtained at a mixing ratio where the flocs became slightly ne gatively charged. Flee size and degradation were observed to be independent of primary kaolin particle size. Furthermore, floc size increased with inc reasing ionic strength. Scanning electron micrographs showed flocs with an open structure, which is expected to improve the optical properties of pape r when using microflocs as a filler in paper production. (C) 2000 Elsevier Science B.V. All rights reserved.