Preparation, thermal stability and decomposition routes of clay/Triton-X100 composites

Abstract

The adsorption isotherms for the octylphenol ethoxylate, TX100, onto a range of bentonites and a saponite have been determined and the resulting thermal stability of composites has been studied. In general TX100 exhibited a high affinity for the different clay surfaces although the maximum amount adsorbed varied with both clay type, layer charge density and resident exchange cation. XRD and variable temperature XRD showed that TX100 was adsorbed into the interlamellar region, and that the thermal stability of the clay/TX100 composite was dependent upon the exchangeable cation present. For monovalent cation exchanged clays (M⁺-clay/TX100) the TX100 decomposed between 220 and 300 °C, and the d₀₀₁ spacing decreased from 15.2 to 9.6 Å. In contrast, divalent cation exchanged clays imparted a greater thermal stability to the complex (M²⁺-clay/TX100) owing to coordination of adsorbed TX100 to the exchange cation, wherein weakly coordinated TX100 was stable to 270 °C and strongly coordinated TX100 was held to temperatures in excess of 300 °C. FTIR analysis of the gases evolved evolved during thermogravimetry confirmed that the octylphenol unit was desorbed from M²⁺-clay at temperatures below 400 °C and that portions of the ethoxylate chain were held to 500 °C.