Surface modication of montmorillonite for polymer-clay nanocomposite preparation

Abstract

The absorption isotherm of alkylammonium salts onto Na-montmorillonite was investigated. Four types of alkylammonium salts of different molecular architecture and chemistry were used for the intercalation process. They are [1] octadecyl trimethyl ammonium chloride (S 18), [2] di-octadecyl dimethyl ammonium chloride (D18), [3] tricaprylyl methyl ammonium chloride (T8) and [4] methyl polyoxyethylene (15) octadecan-ammonium chloride (EO18). The intercalation was done by mixing Na-montmorillonite, having particle size ≤ 2mm, with the alkylammonium salt at 70 ℃. The absorption isotherm was constructed at various alkylammonium loading ranging from 0.25 to 2.5 mmol/g. The obtained organoclay was characterized by thermal gravimetric analysis (TGA) and x-ray diffraction (XRD). As expected, the isotherm was found to depend on the surfactant loading, size, and architecture of the alkylammonium molecule. An effect of the edge shielding of the Na-montmorillonite was done by modifying the clay with silane coupling agent, including octadecyltrimethoxysilane (OTMS) and octadecyldimethylchlorosilane (ODCS). The concentrations of the silane coupling a gent ranging from 0.5- 2.0 mmol/g of clay were employed. The yield point of the silane treated organoclay viscosity was found to be improved over that of an untreated. Polymer-clay nanocomposites were prepared from the organoclay with D18 by in situ intercalative polymerization and melt intercaltion. The conventional composites and intercalated nanocomposites of Nylon6 and polystyrene were found with a high surface coverage organoclay. On the contrary, the intercalation was found to be improved when a low surface coverage organoclay was employed.