Modification Of Alder By Heat Treatment At Medium And High Temperature

In recent years,my country’s North American alder(Alnus rubra f.pinnatisecta)imports have been increasing,and it has been widely used in furniture and interior home decoration.However,problems such as deformation and cracking often occur in solid wood furniture products made of alder wood in North America,which cause economic losses to enterprises.The heat treatment process can effectively improve the dimensional stability and color difference of wood,improve the use value of wood,and expand the application range.However,heat treatment at high temperatures can cause the wood to become brittle,lose its strength significantly,and lose its natural color.In order to improve the deformation,cracking and other defects of furniture products,this study used water vapor as a protective gas to conduct medium and high temperature heat treatment on North American alder wood of M enterprise with 6processes,and systematically studied the influence of various heat treatment process parameters on wood properties.,developed an optimized process,and used the optimized process to process wood,make furniture door parts,and detect the deformation,cracking and warping of the door.The purpose of this study is to effectively improve the dimensional stability of alder wood in North America while minimizing the impact of heat treatment on the mechanical strength and color of the wood.The main research contents and conclusions are as follows:(1)Changes in the physical and mechanical properties of North American alder wood after heat treatment: the weight loss rate increased with the increase of the treatment temperature and the extension of the treatment time,and the treatment temperature and time factors had significant effects on the weight loss rate.The absolute dry density of wood after heat treatment decreased in different amplitude.The heat treatment time has a significant effect on the absolute dry density of the test material.The water absorption of North American alder wood decreased significantly after heat treatment.The hygroscopic equilibrium moisture content and saturated moisture content of heat treated materials in chord,radial and volume are negatively correlated with the degree of heat treatment,and decrease with the increase of temperature and the extension of time.After heat treatment,the chord,radial and volumetric hygroscopic expansion rate and water absorption expansion rate of wood are obviously reduced,which indicates that the dimensional stability of heat treated wood has been effectively improved.The factors of heat treatment temperature and holding time have significant influence on the wet expansion rate of wood in chord,radial and volume.Compared with the control group,the bending strength of the heat treated materials decreased by about 14.27% on average,and the bending elastic modulus of the heat treated materials both decreased and increased under individual heat treatment conditions.The mechanical strength of heat treated material does not show a regular increase or decrease trend with the increase of heat treatment temperature and the extension of holding time.The influence of heat treatment temperature on flexural strength and flexural elastic modulus of wood is very significant,but the influence of holding time on flexural strength is obviously greater than that on flexural elastic modulus.In addition,there is a strong positive correlation between the absolute dry density and mechanical properties of heat treated materials.After heat treatment,the surface color of alder wood in North America changed to different degrees.The overall color darkens,the color develops to red and yellow,and the overall becomes more shiny.The results showed that after heat treatment at 140℃ and 160℃,the overall color difference of wood was 2.55 and 6.00,respectively,which was in a slightly obvious and obvious visual degree,and basically retained the original light color system of North American alder.After heat treatment at 180 ℃,the overall color difference of wood reached 16.74,and the color change before and after heat treatment increased significantly,and the color changed to dark brown yellow.Heat treatment can effectively eliminate the residual stress of wood and reach the first grade drying quality standard after heat treatment.The residual stress values of M enterprise under the condition of 160℃/8h are 0.276 and 0.301,respectively.Heat treatment temperature and holding time have significant influence on reducing wood residual stress.(2)Using the fuzzy mathematics method,four indexes of wood color,size wet growth rate,residual stress and mechanical strength were used as evaluation factors,and the optimization process of this medium and high temperature heat treatment experiment was obtained as temperature 160℃ and holding time 8h.(3)Wood door products with specifications of 1600 mm×450 mm×22 mm(height ×width × thickness)were prepared by using the optimized process heat treatment materials,M enterprise heat treatment materials and untreated materials as the preparation materials,and adopting the right Angle and oblique splicing structure.The results of high and low temperature wet and heat cycle experiment show that the wood door products optimized for heat treatment(160℃/8h)have better moisture resistance and smaller warpage degree.The final expansion rate of size reaches the largest gap between the optimized process and the enterprise process,which is reduced by 12.00% compared with the enterprise process.After the end of the cycle experiment,the warpage degree of the optimized heat-treated wood door was reduced by14.29%(straight)and 65.79%(oblique),respectively.(4)Developed quantitative procedures for optimizing heat treatment process for enterprises,quantified data parameters in material preparation,heat treatment process parameter setting,heat treatment methods and steps,and put forward detailed specification requirements.