Modification Mechanism And Performance Characterization Of Poplar Veneer Simultaneously Treated With Dye And Flame Retardant

Fast-growing poplar is commonly used in the reconstituted decorative lumber.It is an important method to improve the surface decoration effect and flame retardant property of poplar wood that combined dyeing and flame retardant treatment.The acid dyes(GR)and nitrogen and phosphorus(NP)flame retardants were used to simultaneously modify poplar wood in this study.The aim was to simultaneously improve the decorative effect and fire resistance.Furthermore,the different pretreatment and chitosan post-treatment were applied separately to improve the performance of treated wood.Fourier transform infrared spectroscopy(FTIR),thermogravimetric analysis(TG),X-ray photoelectron spectroscopy(XPS),X-ray diffraction(XRD),scanning electron microscope(SEM),and cone calorimetry(CONE)were utilized to reveal the mechanism of poplar wood simultaneously treated with dye and flame retardant.The dyeing effect,wash fastness,light fastness,surface wettability,and flame retardancy were also studied.The effects of the addition of flame retardant on the dye uptake and dye diffusion were analyzed from the dye kinetics perspective.The main results of the study are concluded in the following:(1)In the process of simultaneously treated poplar with dye and flame retardant,there was both promotive and competitive interactions between flame retardant and dye molecules.The NH4+ and H+ of NP flame retardant in aqueous solution weaken the repulsion between the dye matrix(RSO3-)and wood fiber with the same negative charge,thus improving the dye uptake.When the flame retardant concentration was 15%,the dye uptake reached a maximum of 18.02%.The increase in dye concentration reduced the dispersion uniformity of the flame retardant molecules in the solution,which is not conducive to the diffusion of the flame retardant molecules into the wood,resulting in a decrease in the limiting oxygen index.(2)When the temperature was 70 °C,the decomposition of the flame retardant increased.In addition,a large number of flame retardant molecules occupied the pores of the wood,hindering the diffusion of the dye molecules and reducing the diffusion coefficient.At 50 and 60 °C,the flame retardant weakened the repulsion between the dye molecules and the wood,increased the transfer rate of the dye molecules to the wood,and improved the diffusion properties of the dye.The diffusion coefficients increased by 35.27% and 16.84%,respectively.(3)The flame retardant caused a deviation in the color of the surface of the dyed wood,which was shown by the decrease in brightness and chromaticity index of the yellow-blue axis,and the increase in chromaticity index of the red-green axis.The hygroscopicity of the flame retardant increased the rate of decrease of the adhesive’s contact angle on wood surface.K value increased from 0.237 to 0.370.The spread and penetration rate of the adhesive on wood surface increased,thus significantly improving the wettability.(4)The flame retardant treatment reduced the ignition time,peak heat release rate,total heat release and total smoke release of the wood,increased the amount of residual carbon.So the flame retardancy of wood was significantly improved.It is beneficial to broaden the application field and increase added value of poplar.(5)Different pretreatment methods improved wood permeability and provided more penetration channels for dye and flame retardant molecules.After pretreatment,the dye uptake increased,and the limiting oxygen index increased to 37-58%.Hydrothermal treatment improved the surface color stability of poplar wood simultaneously treated with dye and flame retardant.(6)Chitosan could form a continuous film on wood surface,thus preventing the loss of dye and flame retardant molecules from wood.After the modified poplar wood was treated with different concentrations of chitosan,the surface color difference was reduced from 18.892 to 4.509-12.859 for wash treatment,and the leaching resistance of flame retardant was increased from 2.79% to 8.07-23.61%.Chitosan molecules are saturated with chemical bonds and have a stable structure,and the chitosan film was able to reflect and absorb part of the light energy,thus inhibiting the photodegradation reaction of lignin in the wood components.Therefore the light fastness was improved for the poplar wood simultaneously modified with dye and flame retardant.