EVALUATION OF VARIOUS SURFACTANTS AND COMPATIBILIZERS FOR PREPARATION OF PS/CLAY NANOCOMPOSITES BY MELT COMPOUNDING

Thermal stability of selected phosphonium organoclays was compared to that of some ammonium organoclays. Both basal spacing and thermal stability of the phosphonium organoclays indicated the suitability of phosphonium surfactants for the melt compounding of polystyrene (PS)/clay nanocomposites. Surfactants with high molecular weights and organoclays with high values of surface tension at the processing temperature and larger basal spacing yielded the best results. Moreover, several functionalized styrene polymers with terminal polar groups and a styrene-maleic anhydride (SMA) copolymer were evaluated as compatibilizers for the melt processing of PS/clay nanocomposites. Compatibilizers with the higher molecular weights and greater functionality yielded better results. Nanocomposites based on PS/SMA/organoclay yielded nanocomposites with the best levels of intercalation/exfoliation, based on x-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses. Predictions based on surface energy considerations were supported by SEM and energy dispersive x-ray (EDX) element analysis, showing that the clay was preferentially located within the SMA phase or at the SMA/PS interface. The nanocomposites showed marginal improvement in mechanical properties and significant improvement in oxygen barrier behavior.