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This article reports on the influence of the paraffin (PAR) on the wood fiber (WF) dispersion in different polyethylene (low-density polyethylene, high-density polyethylene, recycled polyethylene) matrices, as well as on the melt flow behavior and mechanical properties of WFreinforced polyethylene (PE) composites. In the presence of paraffin, the composites showed improved tensile and flexural strength and modulus, but lower impact strength and elongation at break. The extent of improvement in mechanical properties depends on paraffin content and type of polyethylene; the most effective paraffin was in LDPE-based composites. Paraffin-treated WF showed lower moisture absorption ability in comparison with unmodified wood fiber. The phase segregation process was investigated for PE/PAR blends by DSC method. It was shown that an increase of paraffin concentration in the PE/PAR blend leads to a decrease of PE melting temperature and an increase of paraffin melting temperature; it indicates a net exchange of material from paraffin towards polyethylene. However, generally both components of PE/PAR blends remain immiscible.

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Two different mixers were used for re-compounding of wood fl our / 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, fl exural 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 signifi cant decrease of WPC properties, as long as the properties remain unchanged, if reprocessing was done in extruder. More signifi cant 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.