Abstract
The adsorption of esters of p-hydroxybenzoic acid to magnesium trisilicate and kaolin was examined. Adsorption isotherms at pH 8.0 for 4 esters were linear at low concentration. Adsorption increased with increasing ester chain length. Adsorption was strongly influenced by pH, since the amount of ester adsorbed decreased with increasing pH. Further studies showed that only the non-ionized compound was adsorbed, and this process was Langmuirian. In fact a Langmuirian plot of combined data from the four esters investigated showed that adsorption was independent of the molecular weight and hence the hydrophobicity of the compound. These results suggest that adsorption of the non-ionized compound is a function of the hydroxybenzoate rather than the ester side-chain. In contrast, esters of p-hydroxybenzoic acid were not adsorbed by kaolin.
Published Version
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