FLOCCULATION IN KAOLIN SUSPENSIONS INDUCED BY MODIFIED STARCHES .2. OXIDIZED AND HYDROPHOBICALLY-MODIFIED OXIDIZED STARCH IN COMPARISON WITH POLY(VINYL ALCOHOL) AND CARBOXYMETHYLCELLULOSE

Turbidity fluctuations in flowing kaolin suspensions (1% w/w) were stu died by a fibre-optical sensor technique. From these measurements, a f locculation index (F) was calculated for each of the suspensions. A hi gh value of F indicates a high degree of flocculation. Addition of an oxidized potato starch resulted in substantial flocculation of the sus pension, as was the case when the kaolin was pre-treated with sodium p olyacrylate (NaPA). The flocculation behaviour of the NaPA-treated sus pensions indicated that depletion flocculation is a very likely floccu lation mechanism. When a hydrophobically modified oxidized potato star ch was added to the NaPA-treated suspension, no flocculation occurred and no adsorption of the hydrophobically modified starch on the kaolin particles could be detected. These results are compared with those ob tained when poly(vinyl alcohol) and sodium carboxymethylcellulose were used in place of the starch. The influence on flocculation of the ion ic strength and pre-treatment with sodium polyacrylate was investigate d.