Improvement of rigidity for rubber-toughened polypropylene via localization of carbon nanotubes

A methodology for controlling the localization of multi-walled carbon nanotubes (MWCNTs) was studied using an immiscible polymer blend composed of isotactic polypropylene (PP) and ethylene-co-propylene rubber (EPR). We found that the MWCNTs were localized in EPR domains within the composite, which was prepared at 280 °C. EPR molecules bonded to the MWCNT surface are responsible for the localization in EPR. Conversely, MWCNTs preferentially resided in the matrix when the composite was prepared at 190 °C along with nitrogen gas purging. Because of the selective localization of the MWCNTs in the matrix, the composite obtained via mixing at the lower temperature exhibited a higher Young's modulus and yield strength. These findings demonstrate that mixing conditions greatly affect the MWCNT distribution and thus the mechanical properties of PP/EPR blends.