Effect of carbon nanotubes on morphology evolution of polypropylene/polystyrene blends: understanding molecular interactions and carbon nanotube migration mechanisms

This study investigates the morphological evolution in polypropylene: polystyrene (PP:PS) blends (PP:PS-10 : 90, 30 : 70, 50 : 50, 70 : 30 and 90 : 10 vol%) with 1.0 vol% multi-walled carbon nanotube (MWCNT) loading over the course of melt mixing. Molecular simulation was used to predict the preferential localization of MWCNT in the biphasic blends. The simulation results indicated that the strongly polarized regions in the PS segments have much more interaction with the MWCNT surface in comparison to the weakly polarized PP chains. Transmission electron microscopy showed that MWCNTs are preferentially localized in the PS phase and interphase, regardless of the blend composition, in line with the molecular simulation predictions. Scanning electron microscopy revealed that addition of MWCNT led to significant morphological changes in all PP: PS compositions. When MWCNTs were localized in PS as the minor phase, increasing mixing time enlarged the domain size and enhanced domain interconnectivity in some regions of the samples. We proposed that the migration of MWCNT between the phases played a key role in the morphological changes in the blend nanocomposites. If migration of MWCNT happens among PS domains, then a layer of PS covering the surface of MWCNTs or a PS thread holding MWCNTs facilitates the contact among the domains, hence favouring coalescence.