Properties of biocomposites produced with polypropylene and willow (Salix babylonica L.) wood/bark

The present study investigates the influence of various components of wood-polypropylene composites (WPCs), namely wood (W), inner bark (IB), outer bark (OB), and their blending, on the mechanical behavior. To achieve this objective, willow wood, inner bark, and outer bark flours were used as reinforcements at different weight percentages (17%, 27%, and 40%) in combination with polypropylene (PP) at varying weight percentages (44%, 58%, and 64%), along with a 2% compatibilizing agent. These constituents were processed in a twin-screw co-rotating extruder, with each treatment having a distinct mass proportion of reinforcement to polypropylene. Subsequently, test samples were fabricated using an injection molding machine from the obtained pellets. The mechanical properties of the resulting biocomposites were evaluated in accordance with ASTM standards. It was observed that the flexural and tensile properties of the WPCs improved with increasing inner bark content. Based on the findings of this investigation, a formulation comprising 27% wood, 27% inner bark, 44% polypropylene, and 2% compatibilizing agent (W/IB/PP/MAPP) can be recommended for construction applications requiring high mechanical strength. However, the other reinforced biocomposites exhibited notably lower notched impact strength compared to pure polypropylene.