Starch derivatives of high degree of functionalization: 10. Flocculation of kaolin dispersions

Flocculation properties of cationic potato starch derivatives (2-hydroxy-3-trimethylammonium-propyl starch chloride) with degree of substitution (DS) up to 1.54 were investigated in kaolin dispersions at various solid/liquid ratios and ionic strengths by means of turbidity measurements and colloid titration. It was found that flocculation has occurred long before the kaolin surface charge neutralization was reached. Flocculant amount required for a complete phase separation decreased with the increase of DS, and dispersion restabilization was observed at polymer overdose for all the studied starch derivatives and solid/liquid ratios. The mechanism of the kaolin dispersion flocculation with cationic starch derivatives was suggested to be a combination of bridging and “charge patch” processes. Addition of electrolyte proved to enhance the dispersion flocculation through lowering the required polymer dose and broadening the flocculation window, although no substantial influence of ionic strength on adsorption of the starch derivatives was found.