Influence of magadiite dispersion states on the flammability of polystyrene and polyphenylene ether-polystyrene alloy nanocomposites

A layered hydrous sodium silicate mineral, magadiite, was uniformly exfoliated into polystyrene (PS) matrices to result in a PS/magadiite nanocomposite with high flame-retardant properties. Surface-initiated radical polymerization of styrene from the magadiite interlayer afforded PS graft chains along with exfoliation of each silicate layer to contribute to a uniform dispersion of inorganic nanosheet. The resulting PS-grafted magadiite (PS-g-magadiite) was then mixed with PS homopolymer by a melt-blending process, forming PS/magadiite nanocomposites with fine dispersion of magadiite, which was confirmed by X-ray diffraction, transmission electron microscopy and dynamic mechanical analysis. A series of PS/magadiite composites with various dispersion states and blending ratios were molded into pressed-film-type test pieces to evaluate their flammabilities by cone calorimetric measurements. A peak heat release rate (PHRR) of well-dispersed PS/magadiite nanocomposites was half of that of the PS homopolymer. The dispersibility of magadiite was found to be a crucial factor for improving flammabilities for PS/magadiite composites. Polyphenylene ether-PS/magadiite nanocomposites were also prepared in a similar manner using the PS-g-magadiite nanosheet, but they could not suppress higher PHRR.