Impact of Intensive Mixing and Shearing Elements on the Effectiveness of Extrusion of Wood Polypropylene Composites

The objective of this study was to determine the effect of various design solutions for intensive mixing and shearing elements located at the end of a single-screw plasticizing system on the effectiveness of wood polypropylene composite extrusion. Four types of such elements were used in the study: a pineapple mixer, a Maddock mixer, a ring mixer, and a helical mixer. For the purpose of the study, four blends were prepared containing 5, 10, 15 and 20% of wood fibre, respectively. Direct and indirect resulting factors as well as variable, constant and disturbing factors were investigated. The effectiveness of extrusion of wood polypropylene composites was determined based on results of parameters characterizing this process, such as extrudate temperature, unit consumption of energy supplied to the extruder, mass flow rate, and extrusion speed. It has been shown that the effectiveness of the extrusion process can be improved by using different mixing and shearing elements. Such screw design solutions make it possible to affect rheological phenomena occurring during melt flow in the plasticizing system, without modifying the extrusion process parameters such as screw rotation speed and polymer temperature. The literature review shows that there exist very few and general studies investigating the effect of screw design geometry, especially that of mixing and shearing elements, on the efficiency of extruding and mixing wood polypropylene materials.