Characterization of surface-modified montmorillonite nanocomposites

Montmorillonite K-10 clay was surface-modified using the cationic surfactants viz., butyltriphenylphosphonium bromide (BTPB), cetyltrimethylammonium bromide (CTAB), and tributylhexadecylphosphonium (TBHPB) bromide. Of these, CTAB and TBHPB modified clays were chosen for surface grafting with 3-aminopropyltrimethoxy silane (APTMS) coupling agent. The nanocomposites were fully characterized by powder X-ray diffraction (XRD), solid state 29Si NMR, Fourier transform infrared spectroscopy (FTIR) and thermogravimetry (TGA). The XRD and FTIR confirmed the increase in basal plane spacing and intercalation of long chain surfactant molecules into the clay gallery, while TGA indicated the onset degradation and 10% weight loss temperature (T10%) in case of quaternary phosphonium modified clay that was higher than the corresponding ammonium counterpart; these values increased further after the grafting with APTMS. The 29Si NMR peak deconvolution study suggested that the molar % of T units and total degree of silica condensation for different APTMS grafted clay samples were more than 20% and 80%, respectively.