Effect of polyvinylpyrrolidone and sodium dodecyl sulphate on the dispersity and fluidity of concentrated kaolinite suspension

Abstract

Flow curves for the concentrated suspension of kaolinite (20 g/30 ml-medium) were obtained in the presence of polyvinylpyrrolidone (PVP) and sodium dodecyl sulphate (SDS) by means of a Couette-type rotary viscometer. The flow curves were Newtonian or non-Newtonian, depending on the concentration of PVP and SDS added. From these curves, the plastic viscosity (ηPL) and Bingham yield value (F0) were obtained. The relative viscosity (ηrel) of ηPL with respect to the medium viscosity (η0) were calculated and the contour lines for F0 and for ηrel obtained as a function of the concentration of SDS and PVP added. The feature of these contour lines was qualitatively similar to that for the mean diameter (dm) of the secondary particles in a dilute suspension of kaolinite. It was concluded that both the increase in dm in the dilute suspension and the increase in ηrel and F0 in the concentrated suspension were brought about by the interparticle bridging effect of PVP. The increase inηrel was due to the formation of bulky flow units of large void volume. The increase in F0 reflected the growth of gel structure caused by the bridging effect. It was shown that PVP behaved as a flocculating agent at lower concentrations, but behaved as a dispersing agent at higher concentrations, while SDS at any concentration behaved as a dispersing agent for kaolinite suspension.