Flocculation mechanism of suspended particles utilizing hydrophilic/hydrophobic transition of thermosensitive polymer

Flocculation of suspended particles by a thermosensitive polymer which show s a reversible hydrophilic/hydrophobic transition by heating or cooling its aqueous solution is examined. Poly (N-isopropylacrylamide) (polyNIPAM), wh ose transition temperature is about 32 degrees C, is used as a thermosensit ive polymer. Flocculation experiments were performed by a jar test with kao lin suspension. In the case of operating temperature lower than the transit ion temperature of polyNIPAM, there is an optimum polymer dosage, and by do sing excessively, kaolin particles are stabilized in the same manner as con ventional polymeric flocculants. By heating the suspension above the transi tion temperature under the excess polymer dosage, however, the flee formati on is observed. Furthermore, by cooling the suspension including flocs belo w the transition temperature again, the flocs were disorganized to the stab ilized particles. From these phenomena, it can be concluded that the flee f ormation caused by heating above the transition temperature is due to the h ydrophobic interaction of polyNIPAM molecules absorbed on the particles.