Thermogravimetric analysis of organoclays intercalated with the surfactant octadecyltrimethylammonium bromide

Abstract

High resolution thermogravimetric analysis has been used to study the thermal decomposition of montmorillonite modified with octadecyltrimethylammonium bromide. Thermal decomposition occurs in 4 steps. The first step of mass loss is observed from ambient to 100 degrees Celsius temperature range and is attributed to dehydration of adsorbed water. The second step of mass loss occurs between 87.9 to 135.5 degrees Celsius temperature range and is also attributed to dehydration of water hydrating metal cations such as Na+. The third mass loss occurs between 179.0 and 384.5 degrees Celsius; it is assigned to the loss of surfactant. The fourth step is ascribed to the loss of OH units due to dehydroxylation of the montmorillonite and takes place between 556.0 and 636.3 degrees Celsius temperature range. These TGA steps are related to the arrangement of the surfactant molecules intercalating the montmorillonite. Changes in the basal spacing of the clay with surfactant are followed by X-ray diffraction. Thermal analysis provides an indication of the stability of the organo-clay.