Preparation And Properties Of Silica Modified Plantation Poplar Wood

The plantation poplar is one of the main fast-growing timber species in China,with the largest planting area in the world.However,the fast-growing poplar wood has the problems of low density,soft material,unstable size,flammability and perishability,which greatly limits its application.This paper selected silica powder to prepare silica modifier(S).The effects of the molar ratio of silicon to alkali,reaction time,reaction temperature and the type of alkali material on the solution properties of silica modifier were investigated through orthogonal experiments.Variance and range analysis were used to optimize the process parameters.Furthermore,organosilicone oil and silane coupling agent were used to hybridize the silica modifier,and the composite silica modifier,which is mainly composed of silica solution,was obtained.It had good permeability and high activity.The plantation poplar wood was impregnated with this modifier and then heat treated.The density,mechanical strength,dimensional stability and thermal stability of the treated wood were all improved.Scanning electron microscope(SEM),X-ray diffractometer(XRD),Fourier infrared(FTIR)and nuclear magnetic resonance instruments were used to analyze the distribution and binding form of modifier in modified wood,and the modification mechanism of composite silica modifier was discussed.This will provide a theoretical basis and promote the practical application of wood silicification.The main conclusions are as follows:(1)Based the molar ratio of silicon to alkali,reaction time,reaction temperature and types of alkali materials in the synthetic formula of silica modifier,the L₉(3⁴)orthogonal experiment was carried out,and the average particle size of solution,silica conversion rate,solid content were analyzed.Through comprehensive balance method,the high efficiency liquid activation process of silica powder was obtained,i.e.reaction temperature 200?,base type Na OH,silicon-to-alkali molar ratio 1.715 and reaction time 4 hours.The prepared silica solution was of Si O₂conversion rate 70.9%,modulus 2.43,solid mass fraction 42.8%,average particle size 21.91 nm,p H value 11.55,density 1.361 g·cm^-3,and viscosity 4.8 m Pa·s,this silica modifier has a long storage period,good stability and good permeability.(2)The silica solution was further modified with silicone oil(W-SC₂)and organic coupling agent hybridization(W-HS₂),the solution absorption amount of the treated poplar was more than250%,its absolute dry weight gain rate and density were imcreased more than 45%respectively.W-SC₂ and W-HS₂ had much lower hygroscopicity than W-S.The bending elastic modulus(MOE),bending strength(MOR),and compressive strength of W-SC₂ were 79.8%,68.0%and99.2%higher than untreated wood in turn.The MOE,MOR and compressive strength of W-HS₂were increased by 94.6%,121.5%and 122.6%respectively.(3)The total color difference?E*of poplar wood modified by silica composite and heat exceeded 30NBS,and the brightness L*decreased.The color of TW-SC₂ changed the most.The equilibrium water content of TW-HS₂ was lower than that of W-HS₂ by 21.9%,and its moisture absorption capacity decreased.The MOR,MOE and compressive strength of TW-HS₂ were increased by 111.3%,84.0%and 106.4%respectively.After heat treatment,the color of silica composite modified wood became darker,its moisture absorption capacity was reduced,and its physical and mechanical properties were improved.(4)Through scanning electron microscopy,X-ray diffractometer,Fourier infrared,solid-state nuclear magnetic,cone calorimeter and thermogravimetric analysis,the modification mechanism was discussed.SEM analysis showed that the composite modifier was filled and solidified in the wood cell cavity and partly entered into the cell wall,thus wood was effectively strengthened,and its physical and mechanical properties were significantly improved.FTIR analysis found that the Si-O-Si characteristic absorption peak appeared the silica composite modified wood,which showed that the modifier existed in wood in the way of both chemical combination and physical filling,and wood mechanical properties was greatly improved.²⁹Si nuclear magnetic resonance spectroscopy analysis found that the coordination number around Si atom of TW-HS₂ became larger,indicating that heat treatment can promote the polycondensation and curing of the modifier in wood.Cone calorimeter analysis showed that after the silica composite modification,the ignition time of wood and the time of the second peak of heat release rate were significantly delayed,the total heat release amount and the rate of mass loss were reduced.Thermogravimetric analysis found that the thermal degradation rate of the modified wood decreased significantly,and its thermal stability was improved.The silica composite modification can promote wood carbonization in advance and slow down wood degradation.