The Study On The Modification Technology And Mechanism Of Fururylation Of Wood And Bamboo

The scientific utilization of fast-growing wood and bamboo is one of the most important ways to ease the contradiction between supply and demand of timber. Fast-growing wood and bamboo have the advantage of fast growing and short-rotation, but their performance defects are also very obvious. Therefore, how to overcome the disadvantage of fast-growing wood and bamboo by prolonging their service life and enhancing their commercial value is an major problem during the sustainable development of China’s forestry industry. Furfurylation of wood is an environmental friendly wood modification technology. This process has been regaining increasing attention from industry over the last 10 years. In this paper, a new composite acidic catalyst was developed by our research group to furfurylate poplar, Chinese fir wood, as well as the characteristic fast-growing bamboo resources. In addition, the mechanism of wood and bamboo furfurylation were studied. The study includes two parts as follows:(1) According to the structural characteristics and intended use of the products of the fast-growing poplar, Chinese fir wood and bamboo, weight percent gain(WPG), equilibrium moisture content(EMC), anti-swelling efficiency(ASE), modulus of rupture(MOR), modulus of elasticity(MOE) and parallel-to-grain compressive strength(CS) and durability were selected as evaluating indicators to optimize several key impregnation process, namely furfuryl alcohol(FA) concentration, curing time and temperature.(2) Environmental Scanning Electron Microscope(ESEM) was carried out to obeserve the distribution of furfuryl alcohol resin in the cell lumen and cell wall of wood and bamboo; The laser scanning confocal microscopy was carried out for the observation of distributional difference of furfuryl alcohol resin in the cell lumen against cell wall; nanoindentation was applied to test the hardness and modulus of cell wall of furfurylated wood and bamboo in order to further confirm the exist of FA polymer in the cell wall and evaluate the effect ofmodification on the mechanical properties of cell wall; Infra-red spectrum(FTIR) and nuclear magnetic resonance(NMR) were also applied to clear the modification mechanism between FA polymer and wood and bamboo cell wall.The main research conclusions are as follows:It is very easy for the low-molecular weight furfuryl alcohol to penetrate into wood cells and polymerize during the process. After only once vacuum pressure impregnation process, the highest FA resin retention rate of poplar, Chinese fir and bamboo is up to 60%, 85% and 32%,respectively. The hygroscopicity of wood and bamboo reduced significantly, for instance, the equilibrium moisture content of wood and bamboo reduced by around 40 to 50% conditioned at 23℃ and 65% relative humidity. The dimensional stability of wood and bamboo were also improved significantly. The average of anti-swelling coefficient(ASE) of furfurylated poplar wood were 80%, 92% and 90% in tangential, radial directions and volume. While for the Chinese fir wood, the average of ASE were 71%, 79% and 75% in tangential, radial directions and volume. The ASE of furfurylated bamboo with soaking pressure were on anverage 49%51%, 52% and 51% in the tangential, radial, parallel to the grain directions and volume,respectively.The furfurylated modification endowed the excellent mould resistance properties of wood and bamboo. First, furfurylated poplar and Chinese fir wood showed efficient outstanding anti-mold property, for instance, the anti-mold efficiency reached up to 100% both for Chinese fir wood with only 20% of FA retention rate and bamboo with only 10% of FA retention rate.Furfurylation of wood and bamboo also owned excellent anticorrosion performance resistance to decay fungi. The weight loss ratio was less than 3% for modified poplar and Chinese Fir wood with only 20% FA residual rate and theshape of test specimens kept intact at the end of the test, which belonged a strong decay levels. Overall, the furfurylated wood and bamboo produced conparable results to CCA modified material, and more environment-friendly.Furfurylation of wood and bamboo shows excellent anti-termite properties. Indoor anti-termite test results showed that the weight loss rate was less than 0.7% for furfurylated samples with retained over 20% FA resins.While for the Furfurylated bamboo with 5.4% of FA resin showeda weight loss ratio of 1.76%, belonging to I class termite resistance,and the furfurylated bamboo with 15% of FA resin showed a weight loss rate of 0.82%, and it’s termite resistance level reach to “0” class.The mechanical properties of furfurylated wood and bamboo can be improved with appropriate modification technology. The results showed that the MOR and CS of furfurylated poplar improved remarkably while the MOE showed little improvement. It is not the case with the furfurylated Chinese fir as the mechanical properties under most modification process were reduced.In this paper, orthogonal experiment and single factor experiment were designed to optimize the modification parameters of wood and bamboo. Finally, four optimum process are recommended. A combination of 50% furfuryl alcohol, 105 ℃ curing temperature, and 8 h curing time were proposed as the starting processing parametes for furfurylation of poplar. As for the Chinese fir, 50% furfuryl alcohol, 115℃ curing temperature, and 5 h curing time were proposed. The starting processing parametes for furfurylated bamboo is 15% furfuryl alcohol,105℃ curing temperature, and 3-5 h curing time with vacuum pressure impregnation process.A combination of 50% furfuryl alcohol, 105℃ curing temperature, and 5 h curing time were proposed as the starting processing parametes for furfurylation of bamboo with soaking process under room temperature. Overall, the results show that furfurylation significantly improves the dimensional stability and durability of wood and bamboo. Furthermore, most of the mechanical properties were also enhanced, especially in the case of CS.Scanning electron microscopy and confocal laser microscopy revealed that FA resin was mainly filled in traeheid, vessel cell and wood rays. Furthermore, FA resin covered the inner wall of cells completely, blocking most of the pits on cell wall. The starch granules in bamboo parenchyma cells were dissolved and removed, and some cell cavity was filled with resin.Nanoindentation test results showed thatthe hardness of furfurylated poplar, Chinese fir and bamboo increased by 32, 24 and 65%, with modulus increased by 4, 51 and 53%,The nano-indentation test technology not only revealed that FA resin immersed into cell wall andcured well, but also indicated modification mechanism form the cell wall point, Once improving that FA impregnated wood and bamboo readily.FTIR results indicated that hemicellulose and lignin of wood and bamboo cell wall are degraded during furfurylation. Meanwhile, the characteristic peaks of carbonyl significantly strengthened and offset, indicating that the etherification reaction might occur between FA polymer and wood cell wall compounds during furfurylation of wood and bamboo. There is anther possibility that carbonyl might be introduced by FA polymer. The 13 C CP/MAS NMR of furfurylated wood and bamboo showed superimposed peaks of untreated wood and FA resins at the corresponding chemical shift. In addition, there was no new peaks appeared. Therefore, the results are inclined to support the conclusion of resin filling in the cell wall and cavities of wood and bamboo. It should be noted that it is not able to prove that there is not chemically react between FA polymer and cell wall components of wood and bamboo definitively due to the limited degree of precision laboratory instruments and the accumulation of knowledge.