| Wood modification with furfuryl alcohol(FA),also known as wood furfurylation,is a commercialized wood material modification technology,which can significantly improve the dimensional stability of wood materials.Traditional wood furfurylation technology generally applys vacuum-pressure impregnation process to inject the prepared furfuryl alcohol(FA)modification solution into wood and bamboo followed by curing.However,there are major defects such as the prepared FA modification solution is prone to failure due to prepolymerization,high FA resin consumption,the treated materials is difficult to dry which due to the resin blocks the moisture movement channel,and the treatment of waste liquid is difficult to recycle.These problems restrict the industrial application of wood material furfurylation technology.In this paper,the fast-growing Chinese fir(Cunning lanceolate),poplar(Populus tomentosa)and moso bamboo(Phyllostachys pubescens Mazei ex H.de Lebaie)were used as test materials.Utilizing the characteristics of FA molecules that are relatively volatile and highly polar(with a large amount of hydroxymethyl),a two-step furfurylation via vapor phase furfurylation(VPF)or solution quantitative adsorption furfurylatuin of wood and bamboo based on the precise modification of the cell wall was proposed.These methods solved the problems that were unavoidable in traditional wood furfurylation,and successfully prepared modified wood and bamboo with high dimensional stability and improved mechanical properties.Advanced technologies such as imaging fourier transform infrared spectroscopy(FT-IR)microscopy,nanoindentation,and dynamic vapor sorption(DVS)were used to study the distribution of FA resin in the above furfurylated materials.The main conclusions are highlighted as follows:1.After treatment with six kinds of organic weak acids such as maleic anhydride(MA),the water resistance and dimensional stability of wood and bamboo had been improved.Among them,MA had the best treatment effect,the anti-swelling efficiency(ASE)of treated Chinese fir,poplar and bamboo was 58.98%,43.38% and 14.26%,respectively,which showed that MA have good affinity and esterification ability for wood and bamboo cell walls.In addition,maleic anhydride treatment had no obvious adverse effect on the mechanical properties of wood and bamboo,and the flexural mechanical properties were slightly improved.Therefore,MA was selected as the catalyst for the subsequent precise furfurylation of cell wall.2.The VPF of wood and bamboo by in-situ polymerization in a closed container was used to obtain furfurylated wood and bamboo with low FA resin loading rate and high dimensional stability.On the premise of ensuring the dimensional stability of the furfurylated wood and bamboo,and comprehensively considering the production cost,a parameter combination of 40 h VPF time,115℃ VPF temperature,and 4.5% MA concentration were proposed as the starting processing parameters for VPF of Chinese fir and poplar.As for bamboo,30 h VPF time,125℃VPF temperature,and 4.5% MA concentration were proposed.The furfurylated Chinese fir,poplar and bamboo prepared by the above-mentioned process have ASE as high as 89.00%,80.06% and 51.32%,respectively,under the condition that the weight gain rate was only 10-12%.The equilibrium moisture content(EMC)of treated materials decreased by 38.48%,34.94% and56.28%,respectively,and the compressive strength parallel to grain also increased slightly.3.For the furfurylation of wood in cell walls,there was a threshold of loading rate.When the load rate is less than the threshold,there was a positive correlation between WPG and dimensional stability.If the loading rate was too high,FA has a strong swelling effect on the cell wall,which destroyed the integrity of the cell wall and led to deterioration of the stability of wood performance.4.Using vacuum-assisted vapor phase furfurylation to modify wood and bamboo could significantly enhanced the dimensional stability of materials,the ASE of furfurylated Chinese fir,poplar and bamboo could reach 76.74%,72.28% and 44.59%,respectively.The EMC of furfurylated wood and bamboo was significantly reduced,which was 35.66%,36.10% and 54.45%lower than the control sample,respectively.The use cycle of furfuryl alcohol liquid has increased significantly.Low-temperature auxiliary heating could promote the evaporation of FA molecules and increase the solidification rate,thereby significantly increasing the weight gain gain(WPG)of the modified material,and compared with the treated samples without auxiliary heating,the WPG of Chinese fir,poplar and bamboo were increased about 135%,196% and 103%,respectively.5.The WPG of furfurylated materials could be control well by FA solution quantitative adsorption modification technology.After modification,the WPG of Chinese fir and poplar was between 21-22%,and that of bamboo was about 12%.The dimensional stability of furfurylated Chinese fir,poplar and bamboo was significantly increased,the ASE was as high as 74.14%,71.07% and 53.02%,respectively,and the hygroscopicity dropped by 41.06%,36.55% and55.85%,respectively.Especially the curing rate of furfuryl alcohol exceeded 80%,which was higher than the vacuum-assisted vapor phase furfurylation.6.The distribution of FA resin within wood and bamboo cells treated by the above three furfurylation methods was studied by scanning electron microscope(SEM),nanoindentation and imaging FT-IR spectroscopy.The results showed that: A,the deposition of FA resin in the cell cavity of wood and bamboo could be avoided by the three modification technologies,and the furfurylation could take place inside the cell wall of wood and bamboo.B,The results of nanoindentation showed that the mechanical properties of the cell walls in the outside region of furfurylated wood and bamboo were significantly increased after modification,which indicated that FA could enter the cell wall and solidify well.C,The results of imaging FT-IR spectroscopy showed that: FA could penetrate into the interior of the tested wood and bamboo through different mechanisms via using the three furfurylation methods,and more furfuryl alcohol resin was distributed in the outer region of the modified wood,which made the modified wood show the characteristics of typical gradient materials.7.The modification mechanism of dimensional stability for the three furfurylation technologies was studied,and the results showed: A,through vacuum impregnation,low concentration aqueous solution ensured that the strong polar MA catalyst was only distributed in the cell walls of wood and bamboo,a small portion of MA would have an esterification reaction with cell components which improved the dimensional stability of wood and bamboo.B,the strong polarity and low molecular weight FA could easily enter the cell walls of wood and bamboo in the subsequent vapor phase or solution quantitative adsorption treatment process,and then the polycondensation and cross-linking reactions of FA occurs under the catalysis of MA catalyst and heating conditions,forming hydrophobic FA resin,which played a role in filling the cell wall,thus further improving the dimensional stability of wood and bamboo. |
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