Rheological properties of water dispersions of modified kaolin

Abstract

Background. The use of kaolin as a functional filler for paints will reduce its cost without getting worse its properties. Since the manufacture of paints kaolin subjected to processing in the form of water dispersions, then the possibility of regulation of their rheological properties are important. One way to regulate the rheological properties of water dispersions of kaolin is a modification of surfactants.
The purpose of the article is to establish the influence of surfactants of different nature on the rheological properties of water dispersions of kaolin and identify their rheological parameters depending on the concentration of the modifier.
Material and methods. Object of study is Ukrainian kaolin from Glukhovetsky deposit, which is one of the largest in Europe. As the surfactant modifiers were chosen aqueous potassium methyl siliconate solution and sodium lauryl sulphate. To study the rheological properties of water dispersions of kaolin used method of rheometry. The tests were performed on viscometer Rheotest 2.
Results. Surface treatment of kaolin with aqueous potassium methyl siliconate solution and sodium lauryl sulphate leads to a decrease of structural and mechanical constants.
By increasing the concentration of the modifier reduces static yield stress, the dynamic yield stress and plastic viscosity. Changes are nonlinear and reaches a minimum at the optimum concentration of surfactant. With further increase in the concentration of surfactant the following parameters rise. Each type of surfactant has its own specific optimal concentration.
The dependence of shear stress on aqueous dispersions of kaolin indicate that with increasing concentration of surfactant decreases the value of the last. The presence of hysteresis loops at forward and reverse moves in the modified system confirms the formation of coagulation-adsorption structures.
Conclusion. The modifying of the kaolin by surfactants leads to violation of coagulation links in its structure. Factors of reducing the stability of aqueous dispersions of kaolin are the decrease of plastic viscosity and increasing of static plasticity. The degree of modifier’s influence on the rheological properties of kaolin aqueous dispersions determined by composition and concentration of modifier. Depending on the concentration of the modifier on the surface of kaolin rheological properties of it’s aqueous dispersions could be changed over a wide range.