Morphological changes in sugi (Cryptomeria japonica) wood after treatment with the ionic liquid, 1-ethyl-3-methylimidazolium chloride

We investigated morphological changes in wood tissues of sugi (Cryptomeria japonica) resulting from treatment with the ionic liquid 1-ethyl-3-methylimidazolium chloride ([C2mim][Cl]), which dissolves cellulose. Treatment with [C2mim][Cl] caused dissociation and distortion of tracheids in latewood, but not in earlywood. This difference was due to the difference in swelling behavior of the cell wall between earlywood and latewood. Many pit membranes in bordered pits were broken by treatment with [C2mim][Cl]. In addition, some chemical changes in wood components, such as cellulose and lignin, occurred before significant disruption or destruction of the cell wall. Our results show that the reaction of wood liquefaction by [C2mim][Cl] treatment is not homogeneous, both from chemical and morphological viewpoints.     

Influence of reaction atmosphere on the liquefaction and depolymerization of wood in an ionic liquid, 1-ethyl-3-methylimidazolium chloride

The influence of reaction atmosphere on the liquefaction and depolymerization of wood in an ionic liquid, 1-ethyl-3-methylimidazolium chloride ([C2mim][Cl]), has been systematically studied. The wood samples were treated with [C2mim][Cl] at 120°C under various atmospheres such as oxygen, nitrogen, and carbon dioxide, both dried and humidified. The percentage of residue after the treatment shows that oxygen considerably accelerates the liquefaction of wood in [C2mim][Cl], and humidity hardly affects liquefaction under any atmosphere. Gel permeation chromatography (GPC) and high performance liquid chromatography (HPLC) analyses on the solubilized compounds in [C2mim][Cl] indicate that oxygen and humidity enhance the depolymerization of the wood component. Thus, the reaction atmosphere was revealed to influence, and 1be capable of controlling, the reaction of wood in [C2mim][Cl].     

Morphological changes of Japanese beech treated with the ionic liquid, 1-ethyl-3-methylimidazolium chloride

The morphological changes in wood tissues of Japanese beech (Fagus crenata) upon treatment with the ionic liquid, 1-ethyl-3-methylimidazolium chloride ([C2mim][Cl]), which can dissolve cellulose, were investigated. Treatment with [C2mim][Cl] induced significant swelling of all wood tissues. However, the swelling behavior of wood fibers was different from that of vessels. Intervascular pits were occluded, and pit membranes in ray-vessel pits were broken after treatment with [C2mim][Cl]. No significant differences in swelling behavior were found between latewood and earlywood, although different morphological changes for latewood and earlywood during [C2mim][Cl] treatment were seen in our previous studies on sugi (Cryptomeria japonica). We have found that the effects of [C2mim][Cl] on Japanese beech tissues are inhomogeneous and different from those found for other wood species.     

Comparative study of morphological changes in hardwoods treated with the ionic liquid, 1-ethyl-3-methylimidazolium chloride

Three hardwoods of varying vessel arrangement were treated with the ionic liquid, 1-ethyl-3-methylimidazolium chloride ([C2mim][Cl]), which can dissolve cellulose, to investigate its influence on wood tissue morphology. Characterization was carried out by light and scanning electron microscopy. The wood fibers of all species swelled significantly during [C2mim][Cl] treatment. The swelling behavior varied according to wood species and differed from other cell types such as ray parenchyma cells. Morphological changes of the pits also varied between wood species. Treatment with [C2mim][Cl] affects wood tissues differently depending on wood species and cell type. These differences are not due to the vessel arrangement and its presence, but possibly from the chemical component and the microfibril angle of various wood tissues.     

Reaction behavior of cellulose in an ionic liquid, 1-ethyl-3-methylimidazolium chloride

We investigated the reaction behavior of cellulose in an ionic liquid, 1-ethyl-3-methylimidazolium chloride ([C2mim][Cl]), which can dissolve cellulose. The cellulose samples were treated with [C2mim][Cl] at 100, 120 and 140 °C. At the beginning of the treatment, the solubilized cellulose in [C2mim][Cl] is depolymerized into various low molecular weight compounds such as cellobiose, cellobiosan, glucose, levoglucosan and 5-hydroxymethylfurfural. As the treatment continued, some of the low molecular weight compounds reacted with the ionic liquid to form new polymers, which were black and contained nitrogen. [C2mim][Cl] is, therefore, not only a solvent for cellulose, but also a reagent for both depolymerization to produce various low molecular weight compounds, and subsequent polymerization of those compounds.     

Effect of ozone treatment of wood on its liquefaction

The effects of ozone treatment were investigated to improve the process of liquefaction of wood with polyhydric alcohol solvents. The liquefied wood having a high wood to polyhydric alcohol ratio (W/P ratio) could be prepared by using the wood treated with ozone in the liquid phase. The liquefied wood with a W/P ratio of 2 : 1 had enough fluidity to act as a raw material for chemical products. To get some information about the effects of ozone treatment toward the wood components, cellulose powder and steamed lignin were treated with ozone and liquefied. In particular, ozone treatment in the liquid phase was found to be effective for wood and cellulose powder. On the other hand, steamed lignin self-condensed during liquefaction after treatment with ozone in the liquid phase. Thus, ozone treatment provided lignin with reactive functional groups, and caused the subsequent condensation reaction. Although lignin was converted to a more condensable structure by ozone treatment, the condensation reaction was found to be suppressed for wood during its liquefaction. The wood liquefied products displayed good solubilities in N,N-dimethyl formamide (DMF) even after treatments of long duration. It was suggested that one of the main effects of ozone treatment toward wood was the decomposition of cellulose.Part of this report was presented at the 53rd Annual Meeting of the Japan Wood Research Society, Fukuoka, April 2003     

Ionic liquids as formaldehyde-free wood adhesives

Several ionic liquids promote depolymerization of wood components, i.e., polysaccharides and lignin, into low molecular weight compounds, some of which further re-polymerize into resin-like compounds. In this study, the depolymerization/re-polymerization of wood components in ionic liquids was applied to preparation of plywoods from Japanese cedar (Cryptomeria japonica) veneers by employing ionic liquids as adhesives. The adhesive solution was prepared by mixing an ionic liquid (pyridine hydrochloride ([Py][Cl]), imidazole hydrochloride ([IM][Cl]), or 1-ethylpyridinium chloride ([EtPy][Cl])) with water and d-glucose in various weight ratios. Tensile shear test of the three-ply plywoods prepared from the veneers and the adhesive solution through hot-pressing indicated that the plywood bonded with the [IM][Cl]-based solution ([IM][Cl]/water/glucose ratio: 9/3/2) exhibited the highest strength. Scanning electron microscope observation on the plywoods suggested that the ionic liquids softened the cell walls of the probably plywood through the depolymerization/re-polymerization reactions and the cell walls were compressed during the hot-pressing process. Entwining of the compressed cell walls and van der Waals force enhanced by the compression were considered to be origins of the adhesion of the veneers.     

Analysis on residue formation during wood liquefaction with polyhydric alcohol

Liquefactions of cellulose powder, steamed lignin, alkali lignin, and their mixtures were carried out to analyze the reaction process of wood using polyhydric alcohol. The liquefaction of wood proceeded immediately and wood components were converted to N,N-dimethylformamide (DMF)-soluble components. After that, the condensation reaction occurred with increasing reaction time. However, none of cellulose powder, steamed lignin, and alkali lignin condensed by themselves during their liquefaction. The mixture of cellulose and lignin was also liquefied, and condensed after a long reaction time. The results of analysis showed that the behavior of the mixture resembled that of wood with respect to molecular weight distribution and the main functional groups. Lignin was converted to DMF-soluble compounds in the initial stage of wood liquefaction, followed by cellulose gradually being converted into soluble compounds. After that, condensation reactions took place among some parts of depolymerized and degraded compounds from cellulose and lignin, and were converted into DMF-insoluble compounds. It was concluded that the rate-determining step of wood liquefaction was the depolymerization of cellulose. Furthermore, it was suggested that the condensation reaction was due to the mutual reaction among depolymerized cellulose and degraded aromatic derivatives from lignin or due to the nucleophilic displacement reaction of cellulose by phenoxide ion.Part of this report was presented at the 52nd Annual Meeting of the Japan Wood Research Society, Gifu, April 2002     

Effects of heat treatment on brittleness of <Emphasis Type="Italic">Styrax tonkinensis</Emphasis> wood

A new approach is proposed for the evaluation of the brittleness of heat-treated Styrax tonkinensis wood. Heat treatment made wood more brittle when wood was heated at a higher temperature or for a longer time. The brittleness increased to four times that of the control when wood was heated at 200°C for 12 h. For treatment at 160°C, the increase in brittleness without any change in weight is thought to be possibly caused by the relocation of lignin molecules. At higher temperatures, loss of amorphous polysaccharides due to degradation is thought to become the main factor affecting brittleness. The crystallites that were newly formed after 2 h of treatment showed brittleness that was different from that of the inherent crystallites remaining after 12 h of heat treatment. This inherent crystalline cellulose possibly plays a role in brittleness. There is also the possibility of using color to predict the brittleness of heat-treated wood.     

Reaction behavior of wood in an ionic liquid, 1-ethylpyridinium bromide

The reactions of Japanese cedar and Japanese beech in a pyridinium-based ionic liquid, 1-ethylpyridinium bromide ([EtPy][Br]) were studied. Japanese beech was more easily liquefied than Japanese cedar. Hemicellulose is liquefied rapidly, lignin more slowly, while cellulose is partially liquefied. X-ray diffraction analyses on the [EtPy][Br]-insoluble residues revealed that the crystalline structure of cellulose is maintained even after treatment. The difference in liquefaction can be explained by chemical structural differences between softwood and hardwood lignins and hemicelluloses.     

Liquefaction and product identification of main chemical compositions of wood in phenol

To clarify liquefaction ratios and their construction variations of the main chemical compositions of wood in phenol using phosphoric acid as a catalyst, the chemical ingredients of wood such as holocellulose, cellulose and lignin, were measured and extracted according to GB methods. With Fourier transform infrared （FTIR）, the product identification of reactant before and after liquefaction in phenol was investigated. The molecular weights and their distributions of the liquefaction results （acetone soluble parts） were studied by gel permeation chromatography （GPC）. Results show that the molecular weights and their distributions of poplar and Chinese fir are almost the same. In poplar, the distribution of cellulose is the largest, and that ofholocellulose the smallest after liquefaction. For Chinese fir, the distribution of holocellulose is the largest, and that of cellulose the smallest. After liquefaction of poplar cellulose, the change bands of FTIR spectrum observed below 1 600 cm^-1, can be attributed to new substitute groups. The same is true for poplar lignin. For Chinese fir, the spectra of liquefaction results of all chemical compositions differ from that of wood meal. This reveals the more activity groups were produced because of the reactions between Chinese fir and phenol. The research shows that the liquefaction ratios of poplar decrease in the following order： holocellulose 〉 lignin 〉 cellulose, and those of Chinese fir in the order： lignin 〉 cellulose 〉 holocellulose.     

Chemical analysis of the product in acid-catalyzed solvolysis of cellulose using polyethylene glycol and ethylene carbonate

Degradation and decomposition of cellulose were studied in an acid-catalyzed solvolysis treatment of biomass using polyethylene glycol (PEG) and ethylene carbonate (EC). The solvolysis reaction was followed by a typical reaction system of wood liquefaction that uses sulfuric acid catalyst at 140° or 150°C at atmospheric pressure. The methods of fractionation and chemical analysis of the degraded cellulose in the solvolyzed product are discussed. The solvolyzed product was separated into several fractions, and they were hydrolyzed to release glucose and levulinic acid to determine the quantity of glucosides and levulinates in the solvolysis product. The data clearly showed that the solvolysis reaction had the same mechanism when using PEG or EC. Degradation of cellulose leads to the formation of glucosides, which then decompose, resulting in a levulinic acid structure, and producing a water-insoluble fraction. The conversion rates of both glucosides and levulinates strongly depend on the reaction conditions of the solvolysis. In particular, EC promotes faster conversion of the reactions. The method discussed here is a chemical analytical technique for characterization of the products of wood liquefaction.     

Liquefaction of wood (Metasequoia glyptostroboides) in allyl alkyl imidazolium ionic liquids

The results of wood liquefaction by allyl alkyl imidazolium ionic liquids indicated that wood (Metasequoia glyptostroboides) without any pretreatment is liquefied in ionic liquids at temperatures below 100°C within 40 min. Acidic ionic liquids show low residue even at 70°C and 30 min. The liquid/wood ratio of the reactants affects the reaction course. After the reaction is over, ionic liquids can be separated from the products and recycled at least five times maintaining good liquefaction activity. The suitability of the ionic liquids for wood liquefaction is ascribed to the functional groups of the ionic liquids. Influencing factors of wood liquefaction are discussed in relation to the ionic composition of the ionic liquids.     

木粉及其组分的多元醇酸催化热化学液化

分别将木粉、纤维素和木质素在乙二醇中进行热化学液化。研究结果表明木粉中纤维素的非结晶区、木质素和半纤维素首先被液化,而纤维素的结晶区较慢被液化,到液化反应中期基本降解完全,液化产率高于97%。利用在线红外光谱仪跟踪检测了整个液化反应过程,结合GC-MS结果发现:乙二醇在反应过程中脱水生成了二甘醇和三甘醇。在液化反应中,纤维素的糖苷键断裂后生成葡萄糖苷结构,随后葡萄糖苷中的吡喃环也被打开,生成的活性中间体相互反应或与乙二醇反应生成了如3-(2-甲基-[1,3]-二氧戊环-2-基)-丙酸乙酯、乙酰丙酸丁酯等酯类;木质素的苯丙烷结构主要降解为苯酚、2,6-甲氧基苯酚等芳香族衍生物,因此木粉液化产物是聚醚/酯混合多元醇。     

Preparation of synthetic wood composites using ionic liquids

Synthetic wood composite films containing cellulose, hemicelluloses, and lignin, the three major components of natural wood, were prepared in a room temperature ionic liquid solvent, 1-ethyl-3-methylimidazolium acetate, [EMIM][Ac]. Various synthetic wood composites were obtained by dissolution of individual wood components together with additives, including polyethylene glycol (PEG), chitosan, and multi-wall carbon nanotubes (MWNTs) in [EMIM][Ac]. The addition of water affords a gel that was dried in either a low humidity environment or under vacuum. Synthetic wood films showed smoother surface textures, higher water resistance, and higher tensile strengths than cellulose films formed by the same methods. Tailor-made synthetic wood composites were also prepared having a variety of desirable properties, including antimicrobial activities, controlled hydro-phobicity/philicity, high relative dielectric constant, and a high degree of cohesiveness.     

Reactions between Cr(VI) and wood and its model compounds

Wood, macromolecular and simple model compounds, were reacted with CrO₃ or K₂CrO₄ aqueous solutions. Extracted lignin, guaiacol, vanillin, vanillyl alcohol and homovanillyl alcohol were chosen as model compounds for lignin, whilst cellulose, gum Ghatti, xylan, extracted hemicellulose from pine, methyl-β-D-glucopyranoside and methyl-β-cellobioside were used as models for wood polysaccharides. The kinetics of the reduction reactions of Cr(VI) were monitored using UV-Vis spectroscopy and the results obtained for several temperatures are discussed. In general terms, wood, lignin and lignin model compounds reduced Cr(VI) faster and to a greater extent than polysaccharides or simple sugar molecules. Moreover, lignin model compounds were reduced even faster than lignin. Simple sugars showed a reduction pattern similar to that of cellulose. Extracted hemicellulose revealed to be a poorer reductant while gum Ghatti was the strongest among the polysaccharides. As expected, CrO₃ aq. behaved as a more powerfull oxidant than K₂CrO₄ aq. for these substances. Even at 100 °C, sugars or polysaccharides did not seem to be oxidised by K₂CrO₄ aq. 0.01 M. These results suggest that, because of the differences in reactivity, lignin reacts preferentially when wood is treated with Cr(VI)-containing formulations, like those which are applied in wood preservation treatments.     

Relationship between production of hydroxyl radicals and degradation of wood, crystalline cellulose, and a lignin-related compound or accumulation of oxalic acid in cultures of brown-rot fungi

The degradation of wood, filter paper cellulose, and a lignin-substructure model, was measured in cultures of seven fungi usually regarded as brown-rot fungi. Hydroxyl radical production and the accumulation of oxalic acid in the cultures were also measured. Four of the fungi, Gloeophyllum trabeum, Tyromyces palustris, Laetiporus sulphureus, and Postia placenta, were typical brown-rot fungi, in that they preferentially degraded and eliminated the polysaccharides in wood and produced large amounts of hydroxyl radical. The rates of hydroxyl radical generation in cultures of the four fungi were directly proportional to the degradation rates of wood, cellulose, and the lignin-related compound, and inversely proportional to the amount of oxalic acid in the cultures. Two of the fungi, Daedalea dickinsii and Lentinus lepideus, did not degrade any of the substrates significantly and produced very little hydroxyl radical. Coniophora puteana had the highest rate of cellulose degradation, but did not degrade wood or the lignin model significantly and produced only negligible amounts of hydroxyl radical. These results indicate that brown-rot fungi produce large amounts of hydroxyl radical for the degradation of wood and crystalline cellulose.     

Effects of inorganic acid catalysts on liquefaction of wood in phenol

In order to obtain the effects of acid catalysts on wood liquefaction in phenol, we investigated the liquefaction of wood powder from Chinese fir (Cunninghamia lanceolata) and poplar (Triploid Populus tomentosa Carr) in the presence of phenol with the following weak inorganic acids as catalysts: phosphoric acid (85%), sulfuric acid (36%), hydrochloric acid (37%) and oxalic acid (99.5%). Results show that phosphoric acid (85%) and sulfuric acid (36%) are better than the other catalysts. It was found that lower residue ratios can be obtained under defined reaction conditions: phenol/wood ratio is 4, a 10% catalyst based on the weight of phenol, a temperature of 150°C for 2 h and phosphoric or sulfuric acid. The residue ratios are 3.2% and 4.0%, respectively. __________ Translated from Journal of Beijing Forestry University, 2004, 26(5) [译自: 北京林业大学学报, 2004, 26(5)]     

Chemistry and ecotoxicity of heat-treated pine wood extractives

Pine (Pinus pinaster) wood was heat-treated in an autoclave for 2?C12?h at 190?C210°C. Hemicelluloses were the first compounds affected by the treatment. In general, the sugar decrease was higher for arabinose and galactose followed by xylose and mannose. Lignin started to degrade for small mass losses but at a slower rate than hemicelluloses, and cellulose only degraded significantly for severe treatments. Almost all of the original extractives disappeared, and new compounds arose such as anhydrosugars and phenolic compounds. The compounds that might leach from heat-treated wood were mainly those identified in the water and ethanol extracts, all of which were not harmful at the existing concentrations, thereby reinforcing the wood heat treatment as an environmental benign process.     

Changes of crystallinity in wood cellulose by heat treatment under dried and moist conditions

The different effects of heat treatment on wood, especially on the cellulose crystallites of wood under ovendried and highly moist conditions, were investigated by X-ray diffractometer. Heat was found to increase significantly the crystallinity of wood cellulose; moreover, almost twice as much crystallization was observed after heat treatment of spruce and buna under a highly moist condition than under the oven-dried condition. In pure cellulose almost the same crystallization was observed under both the conditions, whereas more crystallization occurred in wood cellulose than in pure cellulose. Absolute crystallization was observed for the wood species and pure cellulose under both conditions, considering the thermal decomposition of the amorphous region in addition to crystallization. Our results suggested that other components accomparying wood cellulose were involved in the increase of crystallinity by heat treatment, and that wood cellulose contained more quasicrystalline regions than pure cellulose. Moreover, calculated apparent activation energies revealed that crystallization and decrystallization in pure and wood cellulose under heat treatment of highly moist condition were some-what easier than those under the oven-dried condition. The behavior of the piezoelectric modulusd ₂₅ almost paralleled that of crystallinity.