Effect of Re-Compounding on the Properties of Polypropylene / Wood Flour Composites

Abstract

Two different mixers were used for re-compounding of wood flour / polypropylene composites (WPC): internal Banbury mixer and co-rotating twin-screw extruder. Five cycles in an internal mixer and twelve cycles in an extruder were performed on WPC in order to compare the properties of composites. After 3 cycles in an internal mixer, an increase of the WPC mechanical properties (tensile, flexural and impact strength) and a decrease of water uptake was observed. Further increase of the number of cycles in an internal mixer leads to a significant decrease of WPC properties, as long as the properties remain unchanged, if reprocessing was done in extruder. More significant degradation of WPC occurred in an internal mixer compared to the extruder, therefore only 10% of the recyclate prepared in the Banbury mixer and 30% of the recyclate prepared in the extruder can be added to virgin WPC without a decrease of its properties.