Nanostructured Dextran-Graft-Polyacrylamide Flocculants: Effect of Internal Molecular Structure on Flocculative Efficiency

Branched nanostructured copolymers dextran-g-polyacrylamide (D-g-PAA) in uncharged and anionic form were synthesized, characterized, and tested for flocculation in comparison with linear PAA. The polymers differed in the conformation of grafted polyacrylamide chains determining the molecular compactness. Kaolin clay dispersion with a high content (more than 60%) of particles less than 2 μm in size, which settle down with difficulty, was used as a model system. It was shown that branched copolymers exhibited high flocculation activity in noncharged and ionic forms. In contrast to linear polymers, not only the size of the macromolecule polymer flocculants but also their molecular nanostructure affected the parameters (sedimentation rate and degree of supernatant clarification) of the flocculation process. The degree of supernatant clarification for branched polymers at optimal flocculant concentrations was higher than for linear PAA. Branched and linear flocculants in anionic form were tested and compared with respect to flocculation for kaolin dispersion setting as well as for efficiency at removing Cu2+, Co2+, and Ni2+ ions during the flocculation process. Branched molecules were more efficient at trapping heavy metal ions than linear PAA. The ability to remove Ме2+ ions from clay dispersion was greatest for anionic branched copolymers.