Properties Of Sucrose/DMDHEU-Modified Wood Used For Window

Chemical modification can improve the dimensional stability and durability of wood through grafting reaction of the modified agent onto wood cell wall molecules to block the hydroxyl groups,bulking cell wall or/and filling cell lumens.In recent years,modified wood has been applied to floors,doors,windows outdoor decorations and so on.With the development of modification technology,more and more chemical agents applied to modify wood,but some are existing defects such as releasing toxic gases,high cost,waste liquid difficult to deal with.In this paper an environmentally friendly agent--sucrose was used for crosslinking with 1,3-dimethylol-4,5-dihydroxy ethyleneurea(DMDHEU)to modify poplar and pine.The modified poplar and pine wood were processed into windows,then the properties of modified wood and windows were evaluated and analyzed.The weight percent gain of poplar and pine were 57% and 55% after modified with sucrose/DMDHEU,respectively,which improved the density of modified wood effectively.The modified agents deposited in the pine lumens were more than that deposited in the poplar catheter.The bending strength of modified poplar decreased by about 46%,however,modified pine wood increased by about 17%.The modulus of elasticity of modified poplar and pine were increased up to about 51% and 84%,respectively,which enhanced the hardness and toughness of modified wood.The nail holding power was enhanced both in poplar and pine,and tangential sections > radial sections > transverse sections.The tensile strength,shear strength and cleavage strength of modified poplar and pine were decreased in different degrees.The results showed that the hardness,density and stiffness of the modified wood were improved,but the brittleness increased at the same time.Surface free energy and shear strength by compression loading of poplar and pine modified by sucrose/DMDHEU did not show obviously change.That did not affect the general water-based coatings and adhesives spreading wetting of the wood surface.The dry film adhesion can not reflect the strength of the coating adhesion,because some wood chips were pulled off.The hydroxyl groups on the wood surface were increased,which enhanced the hydrogen bonding force and the van der Vaals force,meanwhile the contact area increased with cell inflation.The wet film adhesion of modified wood was slightly higher than unmodified wood.The decrease of moisture absorption improved the dimensional stability of modified wood.During the 27 months of natural weathering,the moisture content of modified poplar and pine were always lower than that of unmodified wood.The lignin is degraded continuously to produce the color changing groups under the effect of ultraviolet light,which lead to the increase of the lightness of the modified wood,and decrease slightly of unmodified wood.The color difference of modified wood was higher than unmodified wood.The wet film adhesion of modified pine was almost not changed but the modified poplar decreased during weathering.Because of the degradation of lignin,the cellulose and hemicellulose were retained to make the surface of the wood feel gully.For the wood windows manufactured by modified and unmodified polar and pine,the performances of windows can all reach Class 8 in thermal insulating properties,Class 8 in air permeability,Class 5 in water tightness,and Class 9 in wind load resistance.Although some mechanical properties of the modified wood were decreased,it did not affect the performances of the wood windows.In summary,the dimensional stability and toughness of wood modified with sucrose/DMDHEU were enhanced,at the same time the brittleness of modified wood was improved.The surface coating and bonding strength were not affected,but the coating adhesion and weathering resistance were improved.The adhesion and nail assembly integration capabilities of the modified wood were improved,but the modified wood should avoid withstanding high loads.The performances of wood windows made by modified wood were as well as the unmodified materials,which met the production and use requirements.