Modification of montmorillonite with cationic surfactants. Thermal and chemical analysis including CEC determination

The thermal stability of synthesized and commercial organically modified montmorillonites has been investigated using thermogravimetric analysis (TGA). Four organo-montmorillonites have been prepared by replacing the inorganic cations of a commercial montmorillonite with aliphatic and aromatic ammonium bromide or chloride salts. The modification has been carried out by cation exchange to obtain a high level of intercalation in the montmorillonite. Conformations of the intercalated surfactants have been characterized using Fourier transform infrared spectroscopy (FTIR). Besides fixed organic surfactant, some surfactant in excess still remained in the montmorillonite after repeated washing with water or ethanol/water. The use of a suitable eluent for the surfactants in the washing step was the key issue as shown by the changes of the first degradation peak of Cloisite-Na+-hexadecyl benzyl dimethylammonium (CLO-BDHA), Cloisite-Na+-benzyl triethylammonium (CLO-BTA) and Cloisite-Na+-hexadecyl trimethylammonium (CLO-HTA). Hexadecyl trimethylammonium (HTA) was more sensitive to water and ethanol/water as eluents. Sonication and the use of a polar activator during the modification of montmorillonite increased the amount of surfactant adsorbed by cation exchange. Ammonium acetate method has been revealed as an adequate chemical method to measure the cation exchange capacity (CEC) of inorganic and organic montmorillonites. This method has the advantage with respect to TGA that it does not measure the unfixed surfactant.