Modification and characterization of bentonite with quaternary ammonium and phosphonium salts and its use in polypropylene nanocomposites

Abstract

Montmorillonite-rich local bentonite was modified with four different quaternary alkyl salts: hexadecyltrimethylammonium bromide ((HMA)(Br)), tetra(kis)decylammonium bromide ((TKA)(Br)), tetrabutylammonium tetrafluoroborate ((TBA)(BF4)), and tetrabutylphosphonium tetrafluoroborate ((TBP)(BF4)) to produce organoclays. The organoclays produced were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis (TGA), and x-ray diffraction (XRD). The XRD results indicate that the d-spacing of the organoclays increased as a consequence of the exchange of Na+ ions in the clay galleries with the cation of the surfactants with long alkyl tails. The d-spacing of the bentonite increased from 1.2 nm to 1.78 nm, 2.56 nm, 1.48 nm, and 1.64 nm after modification with HMA, TKA, TBA, and TBP cations, respectively. TGA analysis of the organoclays showed that the decomposition temperatures of the organoclays were higher than the melt processing temperature of polypropylene (PP), permitting the use of these organoclays in melt processing of PP. Ternary composites of PP/PP-grafted maleic anhydride/organoclays were prepared using a twin screw extruder followed by injection molding for characterization. Transmission electron microscopy analysis of the composites showed intercalated structures as well as microcomposite formations. Mechanical properties of pure PP were improved through ternary composite formation.