The Depolarizing Treatment Of Wood-flour And The Properties Of Wood-plastic Composites

Poplar wood-flour and high density polyethylene (HDPE) were used as raw materials in this study. The effect of poplar wood-flour particle size on the mechanical properties of wood plastic composites (WPCs) was investigated. Poplar wood-flour was modified by maleic anhydride, n-stearylacrylate and silane, respectively. The processing technic of WPCs was optimized. The surface characteristics of unmodified and modified poplar wood-flour was characterized. The interface bonding mechanism between wood-flour and HDPE, and the relationship between the surface characteristics of wood-flour and the properties of WPCs were both studied. The main research contents and conclusions are as follows:(1) The effect of poplar wood-flour particle size on the mechanical properties of WPCs was investigated. The result showed that the tensile modulus and flexural modulus were not significantly affected by particle size in the range studied, there was a slight increase in tensile modulus and flexural modulus as particle size increased. For larger particle size, there was a moderate increase in tensile strength and flexural strength.(2) Poplar wood-flour was modified by maleic anhydride, n-stearylacrylate and silane, respectively. The effect of the content of HDPE, maleic anhydride, n-stearylacrylate and silane on the mechanical properties of WPCs was investigated through orthogonal experiment. The result showed that the optimal content of HDPE, maleic anhydride, n-stearylacrylate and silane was 30%-35%,5%,3% and 2%, respectively.(3) The contact angles of different probe liquids on poplar wood-flour were tested with capillary rise method based on Washburn equation, and the surface free energy and the correspondent dispersion and polar components were calculated according to the method suggested by Owens-wendt-Kaelble. The effect of temperature on the surface free energy and its polar component was investigated. The result showed that the surface free energy and the corresponding dispersive and polar components of the poplar wood-flour were 23.43 mN/m,4.64 mN/m and 18.79 mN/m, respectively. When the treated time was 2 h, as the elevated treated temperature, the surface free energy of poplar wood-flour decreased, its dispersive component which reflected the dispersion force increased, and its polar component which reflected the surface polarity decreased.(4) The surface characteristics of the modified poplar wood-flour were investigated by FTIR. The contact angles of different probe liquids on the modified poplar wood-flour were tested with capillary rise method based on Washburn equation, and the surface free energy and the correspondent dispersion and polar components were calculated according to the method suggested by Owens-wendt-Kaelble. The interface bonding mechanism between wood-flour and HDPE was discussed. The result showed that the strong absorption at 3344 cm-1 that can be seen in all of the FTIR spectra is caused by the remaining OH groups of the fiber constituents, and there is a reduction in the absorbance of this band for modified poplar wood-flour which indicates the reduction of polarity of modified popalr wood-flour. The absorbance at 2921 cm-1 and 2854 cm-1 of the modified poplar wood-flour is due to C-H stretching in the—CH2—and—CH—groups. The surface free energies of modified poplar wood-flour with maleic anhydride, n-stearylacrylate and silane were 48.31 mN/m,46.88 mN/m and 34.37 mN/m, respectively. The corresponding polar components which reflected the surface polarity were 0.4 mN/m, 1.21 mN/m and 3.04 mN/m, respectively. The surface free energy of HDPE was 31.2 mN/m, according to Zisman's theory of critical surface free energy, it was possible for the spreading of HDPE on the surface of the modified poplar wood-flour.(5) The relationship between the surface characteristics of poplar wood-flour and the properties of WPCs was investigated. The result showed that the tensile strength, flexural strength and flexural modulus of WPCs with modified poplar wood-flour were improved greatly. But the water absorption and thickness swelling of WPCs with modified poplar wood-flour were reduced greatly. Moreover, the interfacial adhesion of WPCs with modified poplar wood-flour was better than that of WPCs with unmodified wood-flour. All of these provided evidence for the interface wetting theory. The method of testing the contact angles of different probe liquids on poplar wood-flour and then calculating the surface free energy of wood-flour according to the method suggested by Owens-wendt-Kaelble is a useful and low-cost semi-quantitative measure of the surface characteristics of wood-flour.