| Chinese fir plantation wood[Cunninghamia lanceolata(Lamb.)Hook]is an important fast-growing timber tree species in southern China,with abundant resources.However,because of the soft material,the single color of the material and the unobvious pattern etc,it has been greatly restricted in the practical application.The study of wood dyeing properties of Chinese fir is of great significance,it can improve the visual characteristics and decorative performances and enhance the utilization value of Chinese fir.In this paper,the effects of hydrogen peroxide,sodium hydroxide,and freeze-thaw cycles pretreatment on the dye penetration rate and dye-uptake of Chinese fir plantation wood were firstly compared by a single-factor experiment,then a better pretreatment method for freeze-thaw cycles was selected and optimized by response surface methodology.On the basis of this optimization,the Chinese fir plantation wood was dyed with acid scarlet 3R dye.Four process parameters of dye concentration,dyeing time,dyeing temperature,and dosage of dyeing auxiliary were selected.The dye penetration rate,dye-uptake,and color difference were taken as the investigation indexes.The orthogonal experiments and fuzzy mathematics methods were used for optimization.Finally,based on this,Wood was dyed by adding dicyandiamide to the dyeing solution,chitosan solution coated on the surface of the wood,and water-soluble melamine-formaldehyde(MF)resin and dye mixture made,and the color fastness to hot water and color fastness to UV exposure were tested,compare the effect of these three fixing treatments on the color fastness.The main conclusions of the paper are as follows:(1)Hydrogen peroxide,sodium hydroxide and freeze-thaw cycles pretreatment can improve the dyeing performance of Chinese fir to different extents and the freeze-thaw cycles pretreatment effect is the best,Compared with untreated sample,the maximum dye penetration rate and dye-uptake were increased by 138.21%and 81.86%,respectively;while the dye penetration rate of peroxide and sodium hydroxide pretreatment increased by 45.06%and 76.34%,respectively,and the dye-uptake increased by 71.90%and 73.01%,respectively.The effect of pretreatment on the dye penetration rate and dye-uptake of Chinese fir plantation wood and the effect of these pretreatment methods on the environment were considered seriously,so the freeze-thaw cycles pretreatment method is selected as the basis for subsequent research.(2)Comprehensive analysis of the response values of dye penetration rate and dye-uptake.The optimum process conditions for freeze-thaw cycles pretreatment were soaking time in 24h,freezing time in 16h20min,thawing time in 6h41min and cycle twice.Under the treatment process,The predicted values of dye penetration rate and dye-uptake were 57.52%and 8.51%,respectively,and the average dye penetration rate was 54.10%and dye-uptake was 8.44%in the three confirmatory tests,indicating that the model was reasonable and effective.Compared with the untreated wood,the wood's CSPG(compression strength parallel to grain)through optimize process conditions pretreatment increased by 7.73%,the MOR(modulus of rupture)decreased by 1.86%,the MOE(modulus of elasticity)decreased by 3.31%,the overall change is not obvious.The water absorption gain rate increased by 2.90%within 24h compared to untreated wood.Stereomicroscope observation found that the freeze-thaw treatment wood developed a crack along the radial direction in the transverse.section.Observation by field emission scanning electron microscope(FESEM)revealed that the freeze-thaw treatment caused cracks in the pit membrane of bordered pit,the longitudinal tracheids wall,the middle lamella of longitudinal tracheids and ray parenchyma cells.The results of mercury intrusion porosimetry(MIP)showed that the total pore volume of wood treated with freeze-thaw cycles increased,the surface area decreased and the porosity increased.Fourier transform infrared spectroscopy(FTIR)and X-ray diffraction(XRD)analysis showed that treated wood increased the crystallinity and the chemical composition did not change.Thermogravimetric(TGA)analysis showed that the thermal stability of the treated wood improved,and the residual weight increased.(3)Based on the orthogonal test and fuzzy relation comprehensive evaluation method,the best dyeing process are dye mass fraction in 2.0%,dyeing time in 4h,dyeing temperature at 90?,and dosage of dyeing auxiliary in 3.0%.The average dye penetration rate of the four confirmatory tests under the process conditions was 52.40%,the dye-uptake was 7.31%and the color difference was 52.21.FTIR analysis showed that it was physical absorption primarily between dyes and wood,and FESEM results indicated that a great deal of dyes gathered and were observed in the tracheid,longitudinal tracheid wall,ray parenchyma cells and other microstructure of wood.XRD analysis showed that the crystallinity of the dyed wood was lower than that of the freeze-thaw treatment wood and the characteristic peak of sodium sulfate crystal appears on the diffraction peak.TGA analysis showed that after the freeze-thaw wood was dyed,the thermal stability and the residual weight were increased.(4)Comparing dyes with dicyandiamide,wood chitosan coating,and water-soluble MF resin and dye mixture made.Among them,the color difference of pure dyeing material was 5.16 at 60? water washing for 0.5h and the absorbance value of the soaking solution was 0.8974Abs,and the color difference was 26.37 after 168h UV exposure.The best color fastness to hot water is water-soluble MF resin and dye mixture made composite dyes,its color difference at 60? water washing for 0.5h is 2.57 and the absorbance value of the soaking solution was 0.0960Abs.The best color fastness to UV exposure is wood surface chitosan coating,and its color difference is 22.42 after 168h UV exposure.The triazine ring characteristic absorption peak appeared in the MF resin fixing material by FTIR,indicating that the MF resin was mixed with the dye and cured at high temperature and adhered to the wood microstructure surface.The fixation of chitosan and dicyandiamide is mainly to increase the color fastness by forming the sulfonate form at the interface of wood and dye molecules. |
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