A die-rotating system was proposed in this work for moderations of extrusion forces and entrance pressure drop for molten polypropylene (PP) and wood/ polypropylene (WPP) composites in a capillary rheometer and a single screw extruder. The effects of processing conditions and wood loading in PP were of our interests. The extrusion force and entrance pressure drop with and without the die rotating system were monitored in real-time. This was the first time that the die-rotating system was used for processing of highly viscous wood/polymer composite materials. It was found that the flow properties of the molten PP and WPP composites obeyed pseudoplastic non-Newtonian behavior. The behavior was more obvious at wood contents of above 6 wt % and in the capillary rheometer. The rotation of the die could moderate the extrusion load by 60% and entrance pressure drop by 20% in the capillary rheometer, and the entrance pressure drop by 30% in the single screw extruder, especially at the conditions where the viscosities of the WPP and the extrusion rate were high. Greater fluctuations in entrance pressure drop caused by die rotation were observed in the single screw extruder.
A novel rotating-die system was proposed to moderate the elastic swelling for molten polypropylene (PP) and wood/polypropylene (WPP) composite. The results suggested that the neat PP and WPP melts followed the psuedoplastic non-Newtonian pattern. The rotation of the die could moderate the extrusion load and entrance pressure drop. The die rotation effect appeared to be very pronounced for the PP with high wood contents and high extrusion rates. The decreases in extrusion load and entrance pressure drop were related with reductions of melt viscosity due to shear heating effect. The results practically implied that use of the rotating die system could increase the productivity in the extrusion process. In terms of elastic swelling, in all cases, it was found that the swelling ratio of neat PP and WPP melt composite increased with increasing shear rate, but for any given shear rates, the addition of wood particles and the use of rotating die caused decreases in swell ratio of the melts, the wood content being more well-defined than the die rotating speed.
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