THE SHEAR DEGRADATION OF HIGH-MOLECULAR-WEIGHT FLOCCULANT SOLUTIONS

Solutions of polyacrylamide and poly(acrylamide-co-sodium acrylate) fl occulants with varying molecular weights were shear degraded under a r ange of mixing conditions. The viscosity and flocculant activity of th e solutions generally decreased with time to limiting values dependent on the mixing intensity. The activity of 10 and 20% anionic flocculan ts displayed quite different trends from those for nonionic flocculant s of equivalent molecular weight, with less apparent degradation due t o mixing, particularly at low dosages. However, viscosity measurements on sheared solutions diluted with a salt buffer suggest that nonionic and anionic flocculants with similar initial molecular weights were d egraded to the same degree. Multiangle laser light-scattering measurem ents were used to confirm that the shearing process resulted in a redu ction in molecular weight which was independent of anionic character. The apparent shear resistance of anionic flocculants observed from act ivity measurements was attributed to different flocculation mechanisms for the nonionic and anionic flocculants. (C) 1996 John Wiley & Sons, Inc.