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 studied by a fibre-optical sensor technique. From these measurements, a flocculation index (F) was calculated for each of the suspensions. A high value of F indicates a high degree of flocculation. Addition of an oxidized potato starch resulted in substantial flocculation of the suspension, as was the case when the kaolin was pre-treated with sodium polyacrylate (NaPA). The flocculation behaviour of the NaPA-treated suspensions indicated that depletion flocculation is a very likely flocculation mechanism. When a hydrophobically modified oxidized potato starch 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 obtained when poly(vinyl alcohol) and sodium carboxymethylcellulose were used in place of the starch. The influence on flocculation of the ionic strength and pre-treatment with sodium polyacrylate was investigated.