Phase behaviors and film properties of dispersions and coatings containing associative and conventional thickeners

Abstract

Abstract Phase‐separation behaviors of latex dispersions, using commercial latices of three different median sizes, and pigmented coatings are examined. Both the dispersions and pigmented coatings at a 0.32 volume fraction of total dispersed phase were thickened with water‐soluble polymers, with and without surfactant hydrophobes. Latex dispersions thickened with water‐soluble polymers without hydrophobe modification follow the phase‐separation behavior described by the volume restriction flocculation (VRF) concept (i.e., molecular weight of the thickener or particle size of the latex). This is surprising since commercial latices contain a variety of surface‐stabilizing moieties, in addition to surfactant. Latex dispersions thickened with commercial and model hydrophobically modified ethoxylated urethane (HEUR) polymers do not follow the phase‐separation behavior predicted by the VRF concept. The lack of correlation of phase behavior with latex median size in HEUR‐thickened formulations led to an examination of four secondary thickeners, noted for providing high viscosities at low shear rates. With an all‐acrylic, large median‐size latex, the combinations of commercial HEURs with secondary thickeners are effective in eliminating phase separation; only partial reduction in phase separation is observed with a vinyl acetateacrylic large‐particle latex. The influence of HEUR/secondary thickener blends on the film properties also is discussed. © 1993 John Wiley & Sons, Inc.