Study On Properties Of Wood Modified By Phytic Acid-silica Sol Composite

Phytic acid(PA)is a kind of biomass organic acid,which is green and environmental-friendly.It shows outstanding flame retardancy when applied to wood.However,PA-modified wood produces a mass of smoke during combustion,with poor mechanical properties.Additionally,PA is highly soluble in water.The molecules of PA contain a lot of hydroxyl groups,which will increase hygroscopicity of the treated wood and render PA leach into environmental media easily.All of the matters are unfavorable for the application of PA-modified wood.Targeted at the above problems,PA and silica sol were used to comprehensively modify wood in this study.The vaccum-pressure impregnation method and gel method were adopted to construct a PA/Si O₂network structure inside the wood.These measures could not only improve the flame retardancy and smoke-suppression properties of the PA-modified wood,but also reduce the hygroscopicity of PA in the wood and enhance the leachibility and mechanical performances of the wood.In this study,the morphology and characteristics of PA-silica sol composite(modifying system),in addition to the morphology of the modified wood and distribution of the modifier,were evaluated;the reaction mode of the modification was analyzed;the combustion behavior of the wood were thoroughly assessed,and the underlying flame retardancy and smoke suppression mechanism were examined;the hygroscopicity,leachibility as well as mechanical properties of the wood were evaluated.The primary conclusions are shown as follows:(1)The PA-silica sol was acidic.The average size of particles in the modifying solution was about35 nm.The distribution of the particle size was relatively uniform.PA reacts with Si O₂ to form an amorphous network structure via gelation,and PA is then confined inside.(2)In the PA-silica composite-modified wood,the gel reaction between PA and Si O₂ occurred on the inner wall of the lumen.The crosslinked degree of the PA/Si O₂ gel network increased with the increase of the Si O₂ added.The WPG walues of the composite-modified wood were in 24.99-66.85%range,and the BC values of it were in 7.51-8.28%range.(3)The modification by using PA-silica sol composite can enhance the flame retardancy of wood significantly.The LOI values of the composite-modified wood was above 46.3%,which was approximately twice that of pristine wood,and 21.6%more than that of PA-modified wood.Moreover,the CO and smoke production of the composite-modified wood was significantly lower than that of PA-modified wood,which decreased with the increase of the Si O₂ content.TGA result showed that,the presence of Si O₂ or PA/Si O₂ gel hindered the degradation of wood components and enhanced the thermal stability of wood significantly.Phosphorus and silicon element have synergistic effects of flame retardancy and smoke suppression—P promotes the dehydration of wood components into char,and Si plays the roles of heat shielding and the impediments to transfer and exchange of substances(flammable gases,CO and smoke).(4)The introduction of the silica gel system could decrease the hygroscopicity and leachability of PA to some extent.Compared with that of pristine wood,the absorption rate of the composite-modified wood decreased by 7.3-14.4%,and the ASE values reached more than 23%;the mass loss rate of W-P+25S group reduced by 23.4%,of which the Si O₂ content was 25%.(5)The compressive strength of wood was reduced by the PA modification;in particular,that of the wood with low density decreased more evidently.The introduction of the silica gel system can reduce the effect of PA treatment on the compressive propterty and the tangential-section surface hardness of wood.However,the bending strength and the cross-section surface hardness of the composite-modified wood still need to be further improved.