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

Abstract

AbstractThis study used a newly developed rotating die system for purposes of reducing entrance pressure drop and sharkskin fracture for molten polypropylene (PP) and wood/polypropylene (WPP) composites in a single‐screw extruder. The sharkskin fracture characteristics of the PP and WPP composite surfaces were examined quantitatively via roughness profiles and relaxation time evaluations, and qualitatively through scanning electron microscopy under the effects of wood content, shear rate, die temperature, and die rotation speed. The experimental results suggested that the entrance pressure drop of PP increased with increasing wood content and shear rate. The die entrance pressure drop for WPP composite melt with 30 wt % wood content could be minimized by 20–50% by using a die rotation speed of 70 rpm. The roughness level (sharkskin) and relaxation time were found to increase with increasing wood content, but could be minimized by rotating the die—the die rotating effect being more meaningful for WPP when compared with neat PP extrudate. The rotating die system was found to be an effective technique for minimizing the extrusion load and fracture level of extrudate skins for high‐viscosity materials such as the WPP composites used in this work. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012