Microstructure and mechanical properties of polypropylene/poly (ethylene-co-octene copolymer)/clay ternary nanocomposites prepared by melt blending using supercritical carbon dioxide as a processing aid

To improve the mechanical properties of polypropylene (PP), poly (ethylene-co-octene copolymer) (PEOc) and clay particles were incorporated by melt blending with the aid of supercritical carbon dioxide. Results from X-ray diffraction, electron microscopy, and rheology show that using sc-CO2 makes the clay layers mainly intercalated by polymer chains and well exfoliate in the nanocomposites relative to direct melt blending. This leads to a three-dimensional network structure formed in the nanocomposites as confirmed by rheology. Evidences from scanning electron microscope (SEM) indicate most of clay particles are mainly localized close to or inside the PEOc phase and others disperse separately in the PP phase. The incorporation of PEOc and clay significantly improve the impact strength of PP without the expense of lowering PP's stiffness and strength. The use of sc-CO2 or PP-g-MA during melt-compounding can further improve the mechanical properties of the ternary nanocomposites. Compared to PP-g-MA, sc-CO2 is more favorable for dispersing clay in PP/PEOc blend and improving the mechanical properties of the nanocomposites.