Abstract

Coating colors are very complex colloid systems of which stability and theological behaviors are of importance in the coating process and in the mechanical, optical properties of the coated layer. Clay is one of the main ingredients of coating colors in the paper industry. There can be very complicated colloid interactions that control the stability and theological properties of the coating colors. The main purpose of this work is to get a better understanding about the role of the colloid interactions in the theological behavior of suspensions which are composed of materials having significant meanings in coating color formulations (kaolin, sodium carboxymethyl cellulose, and sodium chloride). For practical applications in many cases, suspensions with a high solid content are required which show low viscosity, significant elasticity, and thixotropy as well. The aim of this investigation is to find such a composition of above components which show the above mentioned theological properties. The colloid interactions were studied by the theological and sedimentation volumes investigations. The results showed that lv (low viscosity) NaCMC was a better stabilizing and thinning agent than my (medium viscosity) NaCMC; NaCl increased the viscosity of CMC added suspensions. 0.01% my NaCMC increased the viscosity of 0.5% lv NaCMC added kaolin suspension supposedly due to bridging flocculation. This is in a good agreement with the results of sedimentation volume investigations. 0.1% lv NaCMC, 0.002% mv NaCMC and 0.5% NaCl together caused the most significant thixotropy, without of NaCl the suspension shows anti-thixotropy. Real-elasticity was only found in the presence of my NaCMC. The samples, prepared from the mixture of low and medium viscosity NaCMCs, were found to be the best composition for getting low viscosity, significant thixotropy and elasticity.