Effects of Surfactant, Electrolytes and Starch on the Rheological Behavior of Bentonite Clay Slurry

Abstract

In the present scenario, almost all industrial operations involve processes with slurries and suspensions. Among the rheological properties, viscosity measurement is the most important one. Since starch and clay slurries are used in the paper and board industry at the time of fillers and pigment coating, the viscosity measurement becomes significant. In this project, the flow rheology was measured in the clay-starch slurry with different additives such as cationic surfactant CTAB and different electrolytes NaCl, Na2SO4 and Na2HPO4 having valency mono, di and tri respectively. Even though starch shows shear thickening property at ambient condition, it showed shear thinning property at a higher temperature 80 ̊C. The addition of starch to the clay slurry increased its viscosity due to the strong interaction between the molecules on the surface of the bentonite clay and Starch slurry since those contain negatively and positively charged surface respectively. Addition of CTAB to the clay-starch slurry increased the viscosity just near to the CMC value due to the strong van der Waals force of attraction between the head group of the CTAB and the clay-starch slurry surface. And the viscosity reduction at and above the CMC value of CTAB was due to the ‘adsorbed bi-layer’ formation. The results conclude that the addition of electrolytes further reduces the viscosity of slurry in the order NaCl> Na2SO4> Na2HPO4. Since the Clion has less charge and the flocculation created by this ion is less as compared to the other two ions which leads to a minimum viscosity. From the FT-IR analysis, it was observed that there were shifting of the peaks in the clay slurry with the addition of starch and CTAB. Which indicates the proper adsorption of the particles on the surface and also the intermolecular interaction between the molecules, which changes the flow rheology. XRD analysis showed that the addition of surfactant and electrolyte reduces the d spacing.