Flocculation and Formation of Open Structure of Kaolinite Suspension in the Presence of Polyvinylpyrrolidone

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Physicohemical and rheological properties of both concentrated and dilute suspensions of kaolinite were studied in the presence of polyvinylpyrrolidone (PVP). Bingham yield value, relative viscosity with respect to the plastic viscosity, volume fraction of the flow unit, and void fraction in the flow unit for the concentrated suspension were estimated from the flow curve obtained by means of a Couette-type rotary viscometer (Shimadzu UR-1). Mean diameter and volume fraction of the secondary particles in the dilute suspension were measured by a Coulter counter (TA-II). The optimum concentrations of PVP for the flocculation of kaolinite (1-50g/100ml), which were obtained by the two measuring methods mentioned above, were consistent with each other. The more the extent of flocculation increased by virtue of the interparticle bridging effect of PVP, the more the volume fraction of the secondary particles, which is ciscometrically effective, increased although the weight concentration of kaolinite was kept constant. This result shows that the floc is of the open structure, and that the void fraction of the floc increases with the extent of the flocculation. The bulky floc, including much of the suspending medium, behaves as a flow unit in the suspension. The open structure was broken up when an excess amount of PVP as a dispersing agent was added.
1988-04-25