Interactions of Stearic Acid with Select Titanium Dioxide Pigments

摘要

The use of stearic acid and metallic stearates in polymer processing has long been practiced and the efficacy of the stearic acid and metal stearates can be related to its availability in the polymer matrix. Often, stearic acid and metal stearates are formulated with solid materials, such as titanium dioxide, in a polymer matrix. The mixture of stearic acid or metal stearates with solids in the polymer matrix provides opportunities for adsorption. The propensity of titanium dioxide to adsorb/desorb stearic acid can be evaluated through the adsorption isotherms. Heats of adsorption/desorption and quantities adsorbed/desorbed for stearic acid over a defined concentration range were measured via flow microcalorimetry for a variety of titanium dioxide pigments. All pigments produced adsorption isotherms consistent with monomolecular adsorption of stearic acid. The adsorption data were fitted to both a Langmuir and a modified form of the Freundlich adsorption model to obtain both capacity factors and intensity of adsorption parameters. Based on limiting adsorption values, stearic acid adsorbs in a predominately vertical fashion. However, some differences were noted based upon surface treatment differences between the individual pigments.