Study On The Weathering Of Wood Modified With An Agent Containing N-methylol Resin/sucrose

Wood is susceptible to precipitation,sunlight radiation and frost during outdoor service,resulting in surface crack,discoloration,mould,and fungal decay.In this study,two woods typically used in Chinese wood industry,domestic produced poplar(Popular adenopoda Maxim)and imported radiata pine(Pinus radiata D.Don)from New Zealand,were impregnated with an agent containing N-methylol resin(1,3-dimethylol dihydroxy ethylene urea)and sucrose(vacuum 0.01 MPa for 1h,following with pressure 0.6 MPa for 2h)and dried at elevated temperatures;the modified/unmodified/coated with five acrylic coatings woods were exposed outdoor in Harbin,(altitude 145-175m,125°42′-130°10’ E、44°04’-46°40′N,a region of the temperate continental monsoon climate with a short rainy summer and a long frozen winter),for 39 months to determine the dynamic change in surface color,cracking/checking,deformation,and moisture content.The findings could be used as a reference for verifying the potentially outdoor application of the modified wood.The results show that both the non-modified and modified woods underwent a color change in first year of exposure.The non-modified wood changed from pale yellow to grey and the modified one from dark brown to grey.This indicates that the modification cannot stabilize wood color during weathering.The modification can considerably restrict the formation of surface cracks in the first 12 months;afterwards both the untreated-and treated woods tended to a comparable degree of cracking.The cracking mode of pine wood was changed by treatment from longitudinal cracking along the cells to cross-section cell fracture;the treatment did not influence the cracking mode of poplar wood.During the outdoor exposure,the modified woods had lower moisture content than their non-modified controls.As a result,the modified woods exhibited lower deformation.The restricting effect to deformation was more obvious on the poplar wood than the radiata pine wood,which is explained by higher dimensional stability of the radiata pine.The FTIR and XRD analyses reveal that the degradation of cell wall compositions was restrained in 12 months of weathering;however,the lignin and cellulosic crystallinity on the surface cells approach to a similar level.This indicates that modification with N-methylol resin/sucrose does not protect the cell wall compositions from a long-term weathering.The microscopic morphology indicates that treatment restrained the detachment of surface cells,especially earlywood cells.As a result,the modified woods still showed a smooth surface but the non-modified woods had a surface like washboard.The modification slows the color change of the coated clear paint within 15 months during the aging process;however,it does not have a protective effect as the paint film breaks.The modification treatment does not affect the penetration of the paint on the surface of the wood to improve the unevenness of the coating on the surface of the wood.The wood finishing and modification treatment synergistically reduce the variation range of wood moisture content,improve the dimensional stability of the wood substrate,and thus reduce the test of the flexibility of the paint film:the substrate modification significantly reduces the aging process of the painted transparent paint film The degree of cracking and spalling.The modification treatment hinders the conduction of moisture along the direction of the wood fiber,improves the adhesion of the paint film,but reduces the transverse tensile strength of the wood.The 39-month aging results show that WF950 and WF980 are not suitable for outdoor use,and the addition of 085E yellow paint improves the durability of the coating system.The WF380 has the potential for long-term outdoor use.Based on the test methods and data in this experiment,a new standard for the natural aging test of coated wood was established in accordance with EN 927-3.In summary,the modification of nitrogen methylol resin/sucrose can effectively inhibit the fluctuation of moisture content,the deformation and the growth of discoloring bacteria in the outdoor aging process of wood,slow down the fading process and component loss,and help to enhance the outdoor durability of wood.Extend the outdoor life of the wood.It is advantageous for the outdoor substrate to be applied to the transparent coating.Extend the maintenance cycle of the painted wood outdoors.The modifier has certain outdoor application potential.