Adsorption of hydrophobically-modified, ethoxylated urethane thickeners onlatex and titanium dioxide disperse phases

Early developments in the use of water-soluble polymers as rheology modifie rs in water-borne latex coatings are discussed, with an emphasis on the ads orption of hydrophobically-modified, ethoxylated methane (HEUR) on the disp erse phases, latex and TiO2. The surfaces of the latex and pigment are dist inctly different and this influences the nature of the adsorption. The amou nt of latex surface acid stabilizer, pH of the dispersion, neutralization c ation, and the median size of the latex are important parameters in the ads orption process. In addition to the associative thickener, there will be va rious types of surfactants in a coating formulation, and their influence on the adsorption of HEURs in aqueous dispersions are considered. When the tr aditional HEUR thickener with only terminally active hydrophobes is used as a thickener and stabilizer, the size and concentration of its terminal hyd rophobes relative to that of the free surfactant are important to the amoun t of HEUR adsorbed. Adsorption on TiO2 offers a significantly different set of variables. The adsorption is influenced by the dispersion's pH and the pK(a), of the metal oxide treatment of the TiO2 surface. Adsorption on thes e surfaces is determined by the acid-base or hydrogen-bonding interactions. When the traditional HEUR thickener with only terminally active hydrophobe s is used as a thickener and stabilizer, interaction with the TiO2 particle requires a preadsorbed co-oligomerized dispersant that contains hydrophobi c groups. This is not a requirement for adsorption when HEURs have hydropho bes placed pendant to the chain (i.e. as teeth in a comb). The comb HEURs a lso appear to destabilize the small particle latex dispersions. (C) 1999 El sevier Science B.V. All rights reserved.