Flow behaviour of titanium dioxide dispersions in the presence of 2-hydroxyethyl cellulose

Abstract

 The effects of 2-hydroxyethyl cellulose (HEC) of weight-average molecular weight 15,000, 90,000 and 7,20,000 on the rheological properties of TiO₂ dispersions were evaluated. For all three HECs, the maximum yield stress, τ_ymax, (occurred at zero zeta potential), decreased with increasing HEC concentration. Interestingly, the largest reduction in τ_ymax was observed with the HEC with the highest molecular weight. This reduction was attributed to steric interaction arising from adsorbed HEC. Adsorbed high-molecular-weight HEC formed an effectively thicker steric barrier because of its larger size and higher adsorption capacity. Bridging interactions that were expected to be important for the high-molecular-weight HEC were found to be unimportant here. In the flocculated regime, HEC enhanced the shear-thinning characteristics of the TiO₂ dispersions.