EFFECT OF SURFACE FREE ENERGY OF WOOD-FLOUR AND ITS POLAR COMPONENT ON THE MECHANICAL AND PHYSICAL PROPERTIES OF WOOD-THERMOPLASTIC COMPOSITES

The primary objectives of this study were to investigate the relationship between surface free energy of wood-flour (WF) and the mechanical and physical properties of wood-high density polyethylene (HDPE) composites (WPCs). The contact angles of different liquids against unmodified and modified poplar WF with 4% n-stearylacrylate were measured with capillary rise methods, the surface free energy and the correspondent dispersive and polar components were calculated based on Washburn equation and the methodology suggested by Owens-Wendt-Kaelble. The results showed that the surface free energy of WF increased from 23.43 mJ/m(2) to 46.88 mJ/m(2), which was higher than the surface free energy of HDPE (31.2 mJ/m(2)), and its correspondent polar component decreased from 18.79 mJ/m(2) to 1.21 mJ/m(2) and the dispersive component increased from 4.64 mJ/m(2) to 45.67 mJ/m(2) after the modification with 4% n-stearylacrylate, which make it ready for the spreading of HDPE on the surface of WF. The tensile strength and flexural strength of WPC samples made with modified WF were obviously improved due to the modification. The water absorption and thickness swelling of WPC samples prepared with the modified WF were lower than those with the unmodified WF which could be attributed to the poor adhesion between the unmodified WF and polymer matrix. The improved compatibility between WF and HDPE was well confirmed by SEM.