A die rotating system for moderations of extrusion load and pressure drop profiles for molten PP and wood/polypropylene composites in extrusion processes

Abstract

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.

Rotating die technique for sharkskin minimization in highly viscous wood/PP composite melt in an extrusion die

“…2(d)], the entrance pressure drop progressively decreased, from 55 × 10 5 to 30 × 10 5 Pa (about a 50% reduction) for low shear rate (2.0 s −1 ), and from 88 × 10 5 to 75 × 10 5 Pa (about a 20% reduction) for high shear rate (7.8 s −1 ), by increasing the die rotation speed from 0 to 70 rpm. The reduction of entrance pressure drop by the action of die rotation speed was associated with two concurrent effects: torsional shear strain and additional shear heating (details of the experimental evidence were given in our previous work) 23. The former can be visualized as a twisting of the flow layers (helical or spiral flows), which is believed to produce torsional shear strain within the die 25.…”

“…The rotating die system that was first developed by our previous work23 was connected to the end of a single‐screw extruder (HAAKE PolyDrive; Thermo Electron), which was used for extruding the WPP composites. The arrangement of the experimental rig is shown in Figure 1 .…”

“…The arrangement of the experimental rig is shown in Figure 1 . The detailed descriptions for each component of the experimental rig can be found in our previous work 23. The exact length‐to‐diameter (L/D) ratio of the barrel was 450/19 mm/mm, and the temperature profiles on the extruder from hopper to die zones were 170, 180, 190, and 200°C.…”

“…Hence, this became an area of interest and inspired this work. More recent work by Intawong et al23 was the original design and manufacture of a rotating die system for reduction of extrusion forces and entrance pressure drop for molten polypropylene and wood/polypropylene (WPP) composites under isothermal and nonisothermal extrusion processes. The experimental results have suggested that the rotation of the die could considerably moderate the extrusion loads and entrance pressure drop, especially with high wood content and at high shear rate.…”

Influence of flow pattern development at die entrance and inside annular die on extrudate swell behavior of NR compound

“…Figure 2a-c shows development of the flow pattern of NR compound occurred inside the barrel of capillary rheometer in a form of Axial Flow (AF) [9,14] , at the piston extrudate rates of 25mm to 100mm with 1.5 s -1 apparent wall shear rate. This resulted from using a die with die gaps of 1mm, 1.5mm, and 2mm, respectively.…”