ADSORPTION OF STARCH ONTO PRECIPITATED CALCIUM CARBONATE

Abstract

The adsorption of polyelectrolytes, native, cationic and anionic starch onto precipitated calcium carbonate (PCC) has been studied on the basis of total organic carbon (TOC) measurements. The aim of this work is to understand the surface charge characteristics of PCC as well as the starches and also to develop a new method to increase the starch adsorption onto PCC. It was estimated that this new method would increase the binding properties of PCC. The surface charges of starches and PCC were determined by measuring the zeta potential. Significant change in zeta potential values were observed with different pH in presence of calcium hydroxide and carbonic acid. Native starch was found to adsorb the most onto PCC .But the mechanism behind anionic starch adsorption could not be predictable. Calcium ions were found to interfere the adsorption mechanism of both native and cationic starches onto PCC thus lowering their adsorption. The adsorption isotherms were also analyzed by Langmuir adsorption model and the experimental data were fitted satisfiLctorily into the non - linear curve. Secondary precipitation of PCC in alkaline and acidic condition have found to have minimum effect on adsorption of both native and cationic starches onto PCC. Cooking of starches along with PCC showed significant effect on adsorption of both starches on PCC. The adsorption of native starch decreased as the cooking was proceeded, while the adsorption of cationic starch increased significantly. An interesting morphology was observed for native starch when it was cooked together with PCC. Some portions of the PCC crystals were tending to form cuboidal structures generating rough surftices. Although the original scalenohedral structure was still maintained.