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.