Study On The Mechanism Of Silicate Modified Chinese Fir And Its Application In Furniture

As an important part of China's artificial forest,Chinese fir(Cunninghamia lanceolata)plays an important role in wood processing,economic construction and ecological environment protection.However,there are some defects of Chinese fir,such as loose structure,light and soft material,low strength and flammability,which limit its wide application in furniture,floor,wood structure and other fields.The existence of aspirated pits in Chinese fir makes the penetration of modifier difficult,and the existing modification methods are difficult to achieve ideal results,which leads to the slow progress in the research of Chinese fir modification.In view of this,this paper takes the fast-growing Chinese fir as the research object,silicate as the impregnating modifier,through the "respiration method" impregnation modification process of negative pressure-positive pressure alternation to modify the Chinese fir.The modified Chinese fir with high quality,high strength,dimensional stability,environmental protection,non-toxic,flame retardant and smoke suppression and other excellent properties was prepared.The modification process,mechanism,basic properties of modified Chinese fir and main properties in furniture application were analyzed.The main research contents and results are as follows:(1)Compared with phenolic prepolymer organic impregnating modifier,sodium silicate inorganic impregnating modifier was more conducive to maintain the environmental characteristics of Chinese fir itself,improve the thermal stability and dimensional stability of Chinese fir,and the impregnation effect was better.Compared with the vacuum step-by-step pressure method,the impregnation modification technology of respiration method can make more modifiers enter into wood,and form more hydrogen bond association and chemical bond with the groups in Chinese fir.At the same time,it can improve the physical and mechanical properties,water resistance,fire resistance and smoke suppression,and heat resistance of Chinese fir.(2)The silicate impregnation modification process of Chinese fir was studied,and the influence rule of various factors on the properties of modified Chinese fir was clarified.On this basis,response surface method was used to optimize the process.The results showed that the influence of each process factor on the weight percentage gain was as follows: impregnation pressure > sodium silicate concentration > impregnation time > respiration time.When the concentration of sodium silicate solution was 31.60%,the impregnation time was 3.80 h,the impregnation pressure was 0.7MPa,and respiration time was 6 times,the impregnation effect was the best.(3)The density,bending strength,compressive strength and impact toughness of Chinese fir were increased significantly after silicate impregnation modification.The three-section quality wear rate and wood water absorption rate decreased significantly.The fire resistance of Chinese fir has been improved significantly,and the effect of flame retardant and smoke suppression was good.The structure of combustion residual carbon was complete.At the same time,the effect of the modified treatment on the color of Chinese fir was small,and the wood basically maintains the original color characteristics.In glossiness,the modified Chinese fir was smaller than that of unmodified Chinese fir,but the distribution rule was basically the same.After modification,the texture spacing,texture thickness and texture density of radial section and tangential section of Chinese fir did not change significantly.Texture gray and background gray were slightly reduced,and the difference between them was larger,making the texture more obvious than unmodified Chinese fir.(4)SEM analysis showed that the negative pressure-positive pressure alternation could destroy the pit plug of the aspirated pit,and open the passage for the penetration and migration of the modifier in Chinese fir.The air inside the wood was discharged,so that the impregnation effect of the wood was better.Compared with the unmodified Chinese fir,the mechanical properties and water resistance of modified Chinese fir were significantly improved by the physical and chemical double effects of silicate modifier.At the same time,the changed of Si element content in radial and transverse direction of modified Chinese fir further verified the effect of respiration method on the opening of aspirated pits.XPS test results was found that C,O,Na and Si elements appeared along the transverse direction from the surface to 30 mm,and the relative content difference was small.The absorption peak intensity of Si-O-C binding structure was basically the same everywhere,which revealed that the modifier was better immersed in the middle of Chinese fir,and the uniformity was good.(5)Based on the analysis model of “windsor chair”,the application of unmodified and silicate impregnation modified Chinese fir in solid wood furniture was analyzed by using Solid Works modeling software and ANSYS finite element software.The results showed that under the fourth level of Chinese national standard,the stress of the structure or component caused by the applied load of the modified wood model was less than the allowable stress of the modified Chinese fir,and the form variable and stress were smaller than that of the unmodified Chinese fir.It was certificated that the structural strength of the chair can meet the requirements of the load standard.It was feasible to use silicate impregnation modified fir wood in the production of solid wood furniture.(6)The contact angle of the water-based paint of Chinese fir was slightly larger than that of the unmodified Chinese fir,and it was still in partial wetting state.The effect of modification treatment on the adhesion of water-based paint on the surface of Chinese fir was less than that of paint type and painting times.When the water-based paint was selected as the surface coating,the type of bottom paint and surface paint can achieve better coating effect,and the times of painting should be 2-3 times for the bottom paint and 2-3 times for the top paint.When choosing the water-based paint with integrated bottom and surface,it should be painted 4 times to obtain satisfactory adhesion performance.The results showed that the bond strength of Chinese fir tenon was improved by 30% and 17% respectively.The best interference fit of mortise and tenon was that when the unmodified Chinese fir was 1.5mm and the modified Chinese fir was 1mm,the pull-out strength and bending strength of mortise joint were the largest.