Effects of Thickening Mechanisms on Dewatering Rate and Filter Cake Formation, 2002 Coating Conference Proceedings

J. Jäder, R. Olsson, I. Wedin and L. Järnström--In this study, we compare ten coating colors containing five different thickeners having different thickening mechanisms with respect to associative and adsorptive properties. Apart from traditional means of coating color characterization, we make use of the previously presented immobilization cell, which permits the simultaneous observation of dynamic dewatering rate and apparent filter cake formation. A comparison of apparent filter cake thicknesses and dewatering rate expressed in terms of the coating color volume vs. square-root of time slope shows that a faster dewatering leads to a higher apparent filter cake at a given time for colors containing carboxymethyl cellulose.  Coating colors based on synthetic thickener (alkali-swellable emulsions) and carboxymethyl cellulose thickeners responded differently to dewatering under shear. The rate of filter cake build-up during dewatering under shear was in general slightly lower for the colors containing carboxymethyl cellulose. Also, the requirements for rapid dewatering seemed to be different. One likely explanation to the mechanism resulting in rapid dewatering for the synthetic thickeners was the high porosity of the cake. This also promotes a rapid build-up of filter cake. For the carboxymethyl cellulose thickeners, on the other hand, a delayed filter cake build-up seemed to result in fast dewatering.