Research On Properties And Mechanisms Of Montmorillonite-and Boron/Phosphorus Compounds-Catalyzed Furfurylated Poplar Wood

Fast-growing poplar wood is abundant,but it is still rarely used as solid wood due to its poor properties.Furfurylation is an environmental friendly cell wall modification method.However,the traditional acidic catalysts cannot meet the requirement of low cost and high performance due to their high reactivity,poor storage stability,and single function,thus restricting its popularization and application in wood modification.In this study,montmorillonite（MMT）and boron/phosphorus compounds were used as functional modifiers of wood and catalysts of furfury alcohol（FA）.In order to improve the dimensional stability,flame retardancy,and decay resistance of fast-growing wood,FA monomers and functional agents were introduced into poplar wood（Populus cathayana Rehd.）under vacuum-pressure impregnation.On this basis,some advanced methods including field-emission scanning electron microscopy,Fourier transform infrared spectroscopy,X ray diffraction,thermogravimetric analysis coupled with Fourier transform infrared spectrometry,and X ray photoelectron spectroscopy et al.were used to analyze the modification mechanism of wood furfurylation.And the curing kinetics of two different systems of FA resin were studied by differential scanning calorimetry to analyze the mechanism of FA curing within wood.The main conclusions of this study are summarized as follows:（1）Sodium montmorillonite（Na-MMT）was transformed into organo-montmorillonite（O-MMT）through ion exchange,resulting increased basal spacing of the interlayers,as well as the change of clay surface from hydrophilic to hydrophobic.The thermal stability of modifiers was improved.The solid acid sites not only catalyzed the decarboxylation and promoted the generation of CO₂ but also promoted the Hoffmann elimination reaction and formed nitrogen compounds.（2）MMT/FA-modified wood were prepared by adjusting the MMT modification method and impregnation technology based on the different targets.In order to improve the dimensional stability and decay resistance of wood,O-MMT was prepared in situ synthesis within wood by inducing didecyl dimethyl ammonium chloride（DDAC）.And it was used in combination with FA to modify wood.At FA concentration of 30%,the modified wood can achieve an anti-swelling efficiency（ASE）value higher than60%and a ML value of 3.2%,which was ranked as high-resistant level in decay resistance.MMT-catalyzed furfurylated wood was prepared by inducing hydrogen ion within clay sheets,thus catalyzing FA curing within wood for flame retardancy.Compared to the original wood,the highest peak heat release rate（PHRR）and total smoke production（TSP）values of MMT-catalyzed furfurylated wood decreased about 31%and 67%,respectively.（3）The introduction of MMT decreased the characteristic temperatures of FA resin,increased the reactive activity at early stage of curing,while its barrier effect reduced the enthalpy of resin curing by13.9%at most.After addition of wood flour（WF）,the characteristic temperatures of FA resin were improved to some extent.And the combined effect of WF and MMT decreased the reactive activity at autocatalytic stage,increased the activation energy at condensation and branching polymerization stage,hindered the motion of FA monomer or linear molecular chains at diffusion stage,thus dropping the enthalpy of resin curing to 514.0 J/g.（4）Boric acid and ammonium dihydrogen phosphate were combined as catalysts for FA and functional modifiers for wood by preparing FA modification solution with excellent storage stability.And the dimensional stability,mold and decay resistance,and flame retardancy of wood were significantly improved.At FA concentration of 15%,the modified wood can achieve a moisture adsorption and water absorption ASE value higher than 47.8%and 59.8%,respectively.After leaching test,the damage value of these modified wood was no more than“1”at anti-mildew performance test and they reached durable level in decay resistance test.After modification,the limiting oxygen index（LOI）value of the treated wood was improved from 25.5%to 34.4%,and the PHRR and TSP decreased about 36%and 97%compared to the untreated wood,respectively.（5）The boron/phosphorus compound catalytic system significantly raised the curing characteristic temperatures of FA resin.And higher temperature should be provided to jointly reduce the reaction activation energy of curing reaction of FA resin.At higher temperatures,the enthalpy of the resin curing reaction were increased by 47.4%,leading higher curing degree and longer curing time.The addition of WF further increased the curing characteristic temperatures,reduced the reaction rate,and required a higher curing temperature（114-130℃）to promote complete curing of the resin.In addition,the addition of wood pushed up the activation energy of resin curing process at the chemical control stage and diffusion control stage.