The effect of extrusion reprocessing cycles on the structure and properties of nano-silica reinforced polypropylene/ethylene-propylene-rubber composites

In this study, the effect of repeated extrusion processing cycles on the structure and properties of polypropylene/ethylene-propylene-rubber/nano-silica composites was investigated. The recycling process was simulated by performing three extrusion runs, using a high shear twin screw extruder by varying the speed screw rotation (300, 800, and 1200 r/min), in order to get better understanding of the multi recycling effects. For comparative purposes, neat polypropylene/ethylene-propylene-rubber was also reprocessed under the same conditions as a reference material. From the morphological analyses performed by scanning electron microscopy, multiple extrusions were found to be not only helpful for decreasing the ethylene-propylene-rubber phase size, but also useful for ensuring a more homogenous dispersion of silica nanoparticles within the matrix. The physico-chemical properties analyses illustrate that the repeated cycles of extrusion processing provoke a decrease of the molar masses and an increase in the melt flow index. It was marked that, when going from the 1^st to the 2^nd extrusion cycle, and by increasing the rotation speed from 300 to 800 r/min at the same cycle, the mechanical properties were greatly enhanced. A substantial improvement of these properties was achieved after incorporating the silica nanoparticles and the maleic anhydride grafted polyethylene copolymer.