Associative polymer/particle dispersion phase diagrams III: Pigments
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The colloidal interactions of both HEUR and HASE associative polymers with pigments in the presence of dispersant are complicated and subject to a number of variables. The objective of this work was to clarify the conditions needed to achieve good pigment dispersion in associative thickener systems by characterizing particle dispersion behavior. This had previously been done for latex particles, but not for pigments such as TiO2. Good dispersion leads to optical properties, such as gloss and hiding, that are superior to nonassociative thicknener systems. Pigment dispersion phase diagrams represent a good way to visualize the complex interactions among pigments, dispersant, and thickener. The two most important variables were found to be pigment type (i.e., surface composition) and dispersant composition. Associative thickners can yield good pigment dispersion or flocculation, depending on the correct matching of dispersants and pigment type. Because of the hydrophobic functional groups governing associative thickner behavior, dispersants having some hydrophobic character yielded the best pigment dipersions and optical properties because they could couple the pigment particles with the associative thickener network. Interior-grade TiO2 tended to yield better dispersions and optical properties than exterior-grade TiO2. Optimized associative thickner systems generally had improved optical properties over comparable nonassociative systems. Optical properties correlated well with particle dispersion behavior as displayed by the dispersion phase diagrams.
KeywordsDispersants thickeners latexes colloids emulsions pigments latex dispersion flocculation hiding titanium dioxide
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