Flocculation mechanism of suspended particles using the hydrophilic/hydrophobic transition of a thermosensitive polymer

Abstract

We examined the flocculation of suspended particles using a thermosensitive polymer which undergoes a reversible hydrophilic/hydrophobic transition when heating or cooling its aqueous solution. As a thermosensitive polymer poly(N-isopropylacrylamide) (polyNIPAM), whose transition temperature is about 32°C, was used. Flocculation experiments were performed by the jar test using kaolin suspension. In the case of operating temperature lower than the transition temperature of poly-NIPAM, there was an optimum polymer dosage, and by dosing excessively kaolin particles were dispersed stably in the same manner as conventional polymeric flocculants. However, floc formation was observed by heating the suspension above the transition temperature under the excess polymer dosage. Furthermore, by cooling the floc-containing suspension down to below the transition temperature again, the flocs were disorganized to the particles. These phenomena show that the floc formation caused by heating to above the transition temperature is due to the hydrophobic interaction of polyNIPAM molecules adsorbed on the particles.