| Chemical modification can improve the dimensional stability and durability of wood via cell wall bulking, hydroxyl group deactivation or lumens filling. This method can improve the comprehensive properties of wood decay and wethering resistance, and can give the special functions such as flame retardant, waterproof on the wood.Sucrose, an environmental friendly natural chemical, is used as a additive for wood modification. A N-methylol resin,1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU) can crosslink the wood polymers and therefore effectively improve the dimensional stability of wood. The solutions containing both sucrose and DMDHEU were used to impregnate veneers of poplar and radiata pine wood, following with hot-pressed to fix the deformation. The properties of the veneers were enhanced at low chemicals loadings by modification of and compression process. This study determined the effects of impregnation/compression on the properties of the resulting veneers, such as springback ratio, density, hardness, color, and mechanical strength.For treatment of poplar and radiata pine with sucrose alone, the sucrose cannot react with wood, and neither condense itself to polymer in the wood cell lumen. While using 10% DMDHEU as a crosslinking agent, sucrose can be fixed effectively in the wood. The optimized fixation ocurred when DMDHEU/sucrose had a ratio of 1:1. Treatment with the mixing solutions caused cell wall bulking up to 7.5% in poplar wood, and up to 7.1% in radiata pine.Densification of the impregnated wood was performed using a hot press, temperature, time and compression ratio were optimized. The selected optimization process is:for poplar, press time of 15 min, pressure at 2.0 MPa, temperature at 160 ℃, and the compression rate 20%; For radiata pine, press time of 20 min, pressure at 2.0 MPa, temperature at 160 ℃, and the compression ratio 20%.Densification and impregnation of poplar and radiata pine with the solution of 5% sucrose and 10%DMDHEU which can reduce the springback rate to 25% and 26% after test in boiling water. Besides, the ASE of poplar and radiata pine were increased to 54% and 60% respectively.The surface density of wood had a greatly increased by the processing of densification. The poplar surface density increased to 0.71g/cm3 from 0.45g/cm3 and the radiata pine to 0.87 g/cm3 from 0.56g/cm3.The rigidity of the wood was enhanced after densification treatment. The bending elastic modulus of poplar and pine wood increased to 10.6GPa and 13.8GPa, respectively. They were treated with 10%DMDHEU and 20%sucrose. The bending and impact strength of the densified poplar and radiata pine were improved slightly after adding a small amount of sucrose, as compared with treated with 10%DMDHEU alone. The compression strength and surface hardness of the densified poplar and radiata pine were increased by adding the sucrose; The compression strength of poplar increased to 9.5MPa from 5.1MPa and radiata pine increased to 10.2MPa from 6.2MPa.The compressed poplar and radiata pine veneer had the highest contact angle when impregnation with 10% DMDHEU alone, the initial contact angle showed an decrease trend with the increase of sucrose concentration. The excessive amounts of sucrose incorporated in the wood caused a decline in bonding strength. The bonding strength can also be improved by the means of pressing the treated wood that had been applied adhesive in advance.The lightness and color of the poplar and radiata pine were darkened with increasing the sucrose concentration increased; However, the grain figure became clear. The coating adhesion and hardness of the compressed wood were improved 40% and 17% approximately by impregnating with sucrose and DMDHEU; The surface abrasion of densification poplar and radiata pine was reduced by 78% and 80% compared with the untreated wood.These results suggested a potential application of the treated/compressed poplar and radiata pine veneers at relatively low chemical loading for surface layer of laminated floor. |
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