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

Abstract

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 1st to the 2nd 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.

The Impact of Reprocessing with a Quad Screw Extruder on the Degradation of Polypropylene

“…Over the three processing cycles in the TSE, the MFI/MFI o increased from 1.3 to 2.0, 1.7 to 3.3, and 2.5 to 5.1 for screw speeds of 500, 1000, and 1500 rpm, respectively. These results were in agreement with other authors' work on polypropylene homopolymers and copolymers reprocessed using single-and twin-screw extruders [9,13,17,18]. At a screw speed of 500 rpm, the QSE produced increases in MFI/MFI o that were similar to those of the TSE.…”

“…These increases indicate that the mechanical work associated with the higher screw speeds increased the levels of shear and made the melt temperature much higher than expected. The findings are consistent with prior work that has shown increases in melt temperature with increasing screw speed [17,27]. Additionally, the melt temperature decreased slightly with a higher number of reprocessing cycles.…”

“…Studying multiple-extrusion history has been found to be a very useful method to simulate mechanical recycling by melt processing [17,18] and to evaluate material processing stability and estimate product properties [18,19]. Several studies of polypropylene have been conducted with co-rotating twin-screw extruders, single-screw extruders, and injection molding machines [7,9,10,[12][13][14][16][17][18][20][21][22][23][24][25].…”

“…Studying multiple-extrusion history has been found to be a very useful method to simulate mechanical recycling by melt processing [17,18] and to evaluate material processing stability and estimate product properties [18,19]. Several studies of polypropylene have been conducted with co-rotating twin-screw extruders, single-screw extruders, and injection molding machines [7,9,10,[12][13][14][16][17][18][20][21][22][23][24][25]. These studies have shown that the degradation during reprocessing is a function of polymer structure, processing method and processing conditions (i.e., temperature, screw speed, screw configuration, and output), and antioxidant efficiency.…”

“…They found that the reprocessed materials presented higher carbonyl indices, higher melt flow indices, and lower average molecular weights when the number of cycles and the melt temperature were increased. When Bouaziz et al [17] investigated the reprocessing of polypropylene at different screw rotation speeds (300, 800, and 1200 rpm) using a twin-screw extruder, they reported that degradation of polypropylene increased with higher screw speeds and a greater number of cycles. Canevarolo [22] investigated the impact of screw design on the degradation of polypropylene with a twin-screw extruder.…”