| In order to characterize properties of wood-flour (WF) and to elucidate their effects on the mechanical properties of wood polymer composites (WPCs), the surface functional groups of modified and unmodified WF were investigated with Fourier transform infrared spectroscopy (FT-IR), the contact angles of different liquids against modified and unmodified poplar WF with 4% maleic anhydride were measured with capillary rise methods based on Washburn equation, the surface free energy and the correspondent dispersive and polar components were calculated through the methodology suggested by Owens-wendt-Kaelble. The results showed that there was a reduction in the absorbance of hydroxyl groups after the modification; the surface free energy of WF increased from 23.43 mJ/m2 to 48.31 mJ/m2, which was higher than the surface free energy (31.2 mJ/m2) of high-density-polyethylene (HDPE), and its correspondent polar component decreased from 18.79 mJ/m2 to 0.4 mJ/m2 and the dispersive component increased from 4.64 mJ/m2 to 47.91 mJ/m2 after the modification with 4% maleic anhydride, which made it ready for the spreading of HDPE on the surface of WF. The tensile strength and flexural strength of the WPC samples produced with the modified WF were obviously improved due to the modification. The improved compatibility between WF and HDPE was well confirmed by scanning electron microscopy (SEM). The high strength accompanying better toughness of the ultra-fine tested steel is correlated with the changes in substructures, i.e. the thickness of pancakes, the width of bainitic packets and denser dislocations pinned by second particles. |
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