Rheological and morphological properties of thermoplastic olefin blends containing nanosilica

This study aims at understanding the rheological and morphological behavior of polypropylene (PP) and ethylene octene copolymer (EC) blends containing nanosilica. Maleic anhydride grafted species of PP and EC were also used to favor the localization of the silica particles in the matrix or in the dispersed phase, respectively. The morphological stability of the blends under flow was investigated by shearing at a very low shear rate of 0.01 s−1. The morphology of the dispersed polymer phases as well as the microstructure of the silica particles inside the nanocomposites were examined using scanning and transmission electron microscopy techniques. Considering the limited time stability of composites with high level of silica loading, the low frequency data of these systems were obtained using dynamic frequency sweep data as well as an extended set of transient creep data reflecting the long time relaxation behavior. The presence of silica particles resulted in an improved morphological stability of all nanocomposites, but the effect was more pronounced when the nanoparticles were localized in the dispersed EC phase. While shearing diminished the viscoelastic properties of the blends containing no silica particle, the sheared nanocomposites with a high concentration of nanosilica revealed enhanced levels of viscoelasticity. This was attributed to the promoted interconnection of solid particles during shearing and the formation of more extended networks as confirmed by microscopic observations.