Development of and results from a chromatographic technique for the analysis of competitive adsorption on stabilized TiO2 surfaces

A unique size exclusion chromatography (SEC) technique is described and used to evaluate the competitive adsorptions of a nonionic formulation surfactant and nonionic Hydrophobe-modified Ethoxylated URethane (HEUR) thickeners on pretreated rutile titanium dioxide (TiO2). The pigment is surface treated with Al2O2 and with SiO2 before it is dispersed by grinding in the preparation of latex coating formulations, Before the latex and thickener are added to this grind, an organic oligomeric acid and a nonionic surfactant are added to the pigment slurry, The organic oligomeric acids used in this study contain maleic acid and one of three alpha-olefins, 1-hexene (C6H12-), 1-decene (C10H20-) or 1-tetradecene (C14H28-) This grind is then let down into the latex formulation containing hydroxyethyl cellulose or HEUR thickener and other components, Without organic dispersant, the nonionic surfactant adsorbs on the silica treated pigment in alkaline media. Adsorptions of the oligomeric polyacid dispersant and nonionic surfactant were higher on TiO2 containing high SiO2 surface concentrations than those containing high Al2O3 surface concentrations. Nonionic HEUR polymers and nonionic surfactants do not adsorb significantly on Al2O3 treated TiO2 unless the pigment is also pretreated with an dispersant possessing pendant hydrophobic groups. Tn competitive adsorption studies the HEUR polymers were not displaced from the organic dispersant stabilized TiO2 surface by the nonionic formulation surfactant. This adsorption behavior contrasts with competitive adsorption studies on acrylic latices when the HEUR polymers have small or intermediate size terminal hydrophobes. The permanence of HEUR adsorption on inorganic and organic dispersant-treated titanium dioxide is consistent with the higher gloss noted in corresponding latex coating systems. (C) 1997 Elsevier Science S.A.