Effect of the addition of a cationic derivative of the natural polysaccharide guar gum on the stability of an aqueous dispersion of alumina

In the present work, the action of a cationic polyelectrolyte (the ammonium hydroxy-propyl-trimethyl chloride of the polysaccharide guar gum, commercially know as cosmedia guar, CG) in aqueous alumina suspension was investigated. This polymer was used aiming to find alternatives for synthetic polymers, as for instance, sodium polyacrylate-PANa, normally used as a deflocculant agent of alumina suspension. Due to its positive charge, this polyelectrolyte (CG) can have electrostatic attractive interactions with the negative charges present on the surface of alumina in alkaline pH. Besides, the presence of hydroxyl groups in this polymer enables attractive interactions with alumina, by means of hydrogen bonds, thus preventing the approximation of other particles and leading to steric stabilization, as occurs when electrostatic attractive interactions (CG/alumina) are present. The study was carried out using the Fiber Optic Quasi-Elastic Light Scattering (FOQELS) technique, aiming to determine particle size. The results obtained with this technique were correlated mainly with those obtained by viscometry. The measurements of particle size, as a function of time, showed that the addition of this polyelectrolytic macromolecule (CG) keeps the particles dispersed for a longer time, in comparison with the suspension containing only alumina.