Effects of heterionic montmorillonites on flame resistances of polystyrene nanocomposites and the flame retardant mechanism

To improve the flame resistance of polystyrene, three kinds of organophilic heterionic montmorillonites (Na-montmorillonite, Ca-montmorillonite, and Fe-montmorillonite) reinforced polystyrene nanocomposites were prepared by melt dispersion method. The structure and composition of the organo montmorillonites were characterized by using X-ray diffraction and Fourier-transform infrared analysis. The adhesion between organo montmorillonites and polystyrene was investigated by scanning electron microscopy. The flame resistance and thermal stability of the polystyrene/organo montmorillonites were evaluated by cone calorimeter test and thermogravimetric analysis. The interlayer space of organo montmorillonites increased with the increase of the oxidation state of the cations. With the addition of organo montmorillonites, the peak values of all the flame resistance indexes of the polystyrene/organo montmorillonites nanocomposites decreased, among which the PHRR values have decreased the most, compared with those of polystyrene. Their corresponding test times have all been delayed following almost precisely the same trend. Therefore, their flame retardant ability come from their lamellated structures, their charring forming abilities, and the reducing power of Fe3+ in polystyrene/Fe-montmorillonite. Organo montmorillonites mainly act as a kind of intumescent flame retardants. The flame resistance of polystyrene/Na-montmorillonite nanocomposite was the best, and the polystyrene/Ca-montmorillonite came second, which is slightly better than that of polystyrene/Fe-montmorillonite.