Nanostructural assembly of cellulose,hemicellulose, and lignin in the middle layer of secondary wall of ginkgo tracheid

Physical, chemical, and biological properties of wood depend largely on the properties of cellulose, noncellulosic polysaccharides, and lignin, and their assembly mode in the cell wall. Information on the assembly mode in the main part of the ginkgo tracheid wall (middle layer of secondary wall, S2) was drawn from the combined results obtained by physical and chemical analyses of the mechanically isolated S2 and by observation under scanning electron microscopy. A schematic model was tentatively proposed as a basic assembly mode of cell wall polymers in the softwood tracheid as follows: a bundle of cellulose microfibrils (CMFs) consisting of about 430 cellulose chains is surrounded by bead-like tubular hemicellulose-lignin modules (HLM), which keep the CMF bundles equidistant from each other. The length of one tubular module along the CMF bundle is about 16 ± 2 nm, and the thickness at its side is about 3–4 nm. In S2, hemicelluloses are distributed in a longitudinal direction along the CMF bundle and in tangential and radial directions perpendicular to the CMF bundle so that they are aligned in the lamellae of tangential and radial directions with regard to the cell wall. One HLM contains about 7000 C₆-C₃ units of lignin, and 4000 hexose and 2000 pentose units of hemicellulose.     

Insecticidal and anti-microbial activity of bio-oil derived from fast pyrolysis of lignin,cellulose, and hemicellulose

Journal of Pest Science - Conflicting views regarding synthetic pesticides include the successful use as pest management tools for agriculture and forestry on one hand and the threats to components...     

Attempts to understand the nature of phenolic and etherified components of wood lignin

Summary Periodate oxidation, because of its high selectivity in degrading phenolic nuclei, has been combined with nitrobenzene oxidation and phenyl nucleus exchange techniques to investigate the nature of wood lignin in situ. For both softwood and hardwood, the phenolic and etherified components of wood lignin have been shown to differ significantly in chemical composition, and the etherified lignin structure appears to be substantially more condensed.Financial support from the Empire State Paper Research Associate (ESPRA) and by the NRICGP of USDA (No. 93-37103-9318) is greatly appreciated     

Contribution of lignin to the reactivity of wood in chemical modifications I: influence of delignification on acetylation

In order to examine the contribution of wood components to the acetylation of wood, we acetylated wood meal that had been partially delignified. The results were analyzed in terms of the reaction kinetics. The first-order rate equation was successfully adjusted to the weight gain data. The rate constant for acetylation initially increased with progress of lignin elimination and then turned to decrease; the apparent activation energy showed the reverse tendency and ranged from about 90 to 130 kJ/mol. These results suggest that lignin elimination brings not only separation of lignin but also drastic change of the chemical and/or physical structure in the residual lignin, and this affects the reactivity of wood meal as a whole. The ultimate weight gain estimated by the regression of the rate equation showed a minimum when lignin was moderately eliminated, which was explained in terms of enhanced reactivity of lignin and lower accessibility for holocellulose than predicted. The equilibrium moisture content had a maximum when lignin was moderately eliminated. This tendency is the opposite of that observed for the ultimate weight gain, and suggests that the sites for acetylation do not always correspond to those for moisture adsorption. Part of this report was presented at the 54th Annual Meeting of the Japan Wood Research Society, Sapporo, August 2004     

脲醛树脂胶粘剂添加剂不同配比研究*

为降低生产成本、开发新型木材胶粘剂添加剂,选用羧甲基纤维素钠和细沙为主要原料,面粉为辅料,并研究其成分配比对胶粘剂人造板产品质量及加工成本的影响。结果表明：当添加剂中羧甲基纤维素钠、面粉、细沙质量百分比为3∶30∶67时,成本比传统添加剂降低了33%,面粉使用量减少了70%。     

Distribution of lignin in normal and tension wood

Summary The distribution of lignin in normal and tension wood of four hardwood species has been studied by examination in the electron microscope of the lignin skeletons remaining after removal of the polysaccharides with hydrofluoric acid. In normal wood fibers, the S₁ had a higher lignin concentration than the S₂ layer, which was not as highly lignified as in conifer tracheids. Vessels had a high concentration of lignin in both normal and tension wood, while the extent of lignification of the parenchyma was variable.In tension wood fibers, the S₁ and S₂ layers were highly lignified. A thick, unlignified G-layer was often associated with an extremely thin S₂ layer with a high concentration of lignin. In both normal and tension wood, the lignin had the same orientation as the cellulose micro-fibrils in the different cell wall layers. The results confirm the earlier conclusion that, in the species investigated, the same amount of lignin is present in gelatinous as in normal fibers. Evidently, the lignification mechanism operates normally in the non-gelatinous layers of the fibers, as well as in the vessels and in the parenchyma of tension wood.

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Zusammenfassung Die Ligninverteilung im Normalholz und im Druckholz von vier Laubhölzern wurde untersucht. Die Ligningerüste, die nach der Entfernung der Polysaccharide durch Fluorwasser-stoffsäure übrigblieben, wurden im Elektronenmikroskop beobachtet. In den Normalholzfasern hatte die S₁-eine höhere Ligninkonzentration als die S₂-Schicht, die weniger lignifiziert war als in den Koniferentracheiden. Die Gefäße hatten eine hohe Ligninkonzentration in sowohl Normal-als in Zugholz, während der Lignifizierungsgrad der Parenchymzellen variierte.In den Zugholzfasern waren die S₁- und S₂-Schichten völlig lignifiziert. Eine dicke, unlignifizierte G-Schicht war oft mit einer außerordentlich dünnen S₂-Schicht, die eine hohe Ligninkonzentration zeigte, verbunden. Sowohl im Normal- wie auch im Zugholz besaß das Lignin dieselbe Orientierung wie die Cellulosemikrofibrillen in den verschiedenen Zellwandschichten. Die Ergebnisse bestätigen den früheren Schluß, daß in den hier untersuchten Laubhölzern in den gelatinösen und in den normalen Fasern dieselbe Ligninmenge vorliegt. Offenbar läuft der Mechanismus der Lignifizierung in den S₁- und S₂-Schichten der gelatinösen Fasern des Zugholzes normal ab.

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This investigation was supported by the United States Department of Agriculture, Forest Service, through Forest Service Research Grant No. 1, which is hereby gratefully acknowledged.     

Determination of the cellulose and lignin content on wood fibre surfaces of eucalypts as a function of genotype and site

We compared the chemical composition of wood fibres and fibre surfaces of several eucalypt species and hybrids originating from various growth sites in South Africa. The objective was to test for differences in chemical surface composition due to genetics or site with the ultimate aim to facilitate a tailor-made supply of wood for pulping that results in an optimal blend of fibres that can be pulped together with similar yields. This, however, requires a sound knowledge of the fibre properties. The surface functionality on the single fibre level is a key property, because it determines how good inter-fibre bonding will be when paper is formed, which depends amongst other fibre properties on the amount of free hydroxyl groups that are available and therefore on the cellulose content on the fibre surface. The cellulose and lignin content on the fibre surface were determined with chemical force microscopy, a variation of atomic force microscopy. Since the general bulk composition of the fibre and the surface composition might differ, both parameters were determined. We found significant differences in the cellulose and lignin content on fibre surfaces, with regard to genotype and site, respectively. In some, but not all, cases, the surface composition of wood fibres followed the bulk composition, and differences were generally more pronounced. Differences due to genotype were significant, especially with regard to the surface lignin content—but variation due to site was also distinctly recognisable. This variation in surface functionality could be the reason why some pulpwood blends result in a lower pulp yield and different quality.     

Enzymatic degradation of cellulose,cellulose derivatives and hemicelluloses in relation to the fungal decay of wood

Summary Cellulases and hemicellulases (mannanase and xylanase) from culture filtrates of various fungi, including a brown rot fungus, Polyporus schweinitzii and a soft rot fungus, Chaetomium globosum, have been isolated and characterized. Investigations of their molecular weights, pH- and temperature optima and stabilities indicate that hydrolases of the wood destroying fungi are very similar to one another and to hydrolases from various other plant organisms. Substrate specificities and the effect of substituents on the natural substrates have also been investigated. Routine tests for mannanase and xylanase were carried out with model substrates (mannan from Tubera salep, xylan from wheat straw), but preliminary tests with complex hemicelluloses isolated from wood showed that these too could be broken down to monoor oligosaccharides. The results presented are discussed in relation to possible roles of the various enzymes in vivo.Paper presented at the Int. Wood Chemistry Symposium, Seattle, 3. IX. 1969.With support of the Deutsche Forschungsgemeinschaft.     

Degradation of wood surfaces during natural weathering. Effects on lignin and cellulose and on the adhesion of acrylic latex primers

Summary Radiata pine veneers and blocks were exposed to natural weathering under Australian summer conditions over a period of 30 days. Infrared spectroscopy revealed that there was perceptible surface delignification after 4 hours exposure, substantial surface delignification after 3 days exposure and almost complete surface delignification after 6 days. Rapid lignin degradation was also suggested by measurements of the acid insoluble lignin content of weathered veneers. Viscometry determinations on holocellulose samples from weathered veneers and unweathered controls indicated significant depolymerisation of cellulose after 4 days exposure. A tape test was used to assess the adhesion of acrylic latex primers to weathered blocks. The adhesion of exterior acrylic primers decreased on weathered wood surfaces and was significantly lower on specimens that were weathered for 5 to 10 days. An oil-modified acrylic primer showed greater adhesion to weathered wood surfaces. Primer adhesion was lower on weathered radial surfaces than on similarly exposed tangential surfaces. The practical implications of these findings for the coating of exterior wood with acrylic latex primers are discussed briefly.The authors wish to thank Dr. A. J. Michell for FTIR spectral determinations and the Australian Research Council small grants scheme for financially supporting part of the work     

A comparative study of bamboo (Phyllostachys incarnata Wen) milled wood lignin and the successively alkali-fractionated lignins

The chemical composition and structural characterization of the milled wood lignin (MWL) and successively alkali-fractionated lignins from bamboo (Phyllostachys incarnata Wen) were comparatively investigated using Fourier transform infrared (FT-IR), gel permeation chromatography (GPC), 2D heteronuclear single quantum coherence (HSQC), and alkaline nitrobenzene oxidation. It was found that bamboo MWL (S/G?~?1.3) is of SGH type with a considerable amount of esterified p-coumaric acid and etherified ferulic acid. Molecular weights of 3,320?g/mol for MWL and varying weights between 970 and 3,430?g/mol for the alkali-fractionated lignins were obtained. Moreover, 2D HSQC of MWL showed a predominance of β-O-4′ linkages (65%), followed by β–β′ linkages (15%) and lower amounts of β-5′ (7%), β-1′ (4%), 5–5′ (4%) linkages, and cinnamyl acetate end groups (5%). In addition, a percentage (~45%) of the lignin side chain was found to be acylated at the γ-carbon. However, the alkali-fractionated lignins lost parts of these linkages during successive alkaline fractionation processes.     

Comparative study of anatomy and lignin distribution in normal and tension wood of Salix gordejecii

Fibre morphology, anatomy and ultrastructure in cell wall of Salix gordejecii normal wood were examined by transmission electron microscopy (TEM). S. gordejecii tension wood can be recognized anatomically by the presence of gelatinous (G) fibres, which contain a conspicuously thickened inner cell wall layer. TEM images showed that cell wall of S. gordejecii normal wood was typically divided into three layers including the primary wall (P), the middle lamellar (ML) and the secondary wall (S₁, S₂ and S₃). Lignin distribution was determined by using confocal laser scanning microscopy (CLSM) and transmission electron microscopy with energy dispersive X-ray analysis (TEM-EDXA). Confocal images (530 nm) of S. gordejecii normal wood showed strongly lignified CCML, and weakly lignified ML and S2 layer. Weakly lignified fibres (F) and strongly lignified vessels (V) were also detected by using CLSM. Results obtained from confocal microscopy were further confirmed by using TEM-EDXA, indicating that the ratio of lignin concentration in CCML, ML and S2 is 1.72 (1321):1.31 (1006):1 (768). Lignin distribution in tension wood is similar to that in normal wood, except for the non-lignified G layer.     

Non-uniform reaction of solid wood in vapor-phase acetylation

To clarify the non-uniform reaction of wood during vapor-phase acetylation, spruce wood blocks were exposed to acetic anhydride vapor at 120°C. Weight percent gain (WPG) due to the acetylation was estimated from the equilibrium moisture content at 25°C and 60% relative humidity. The diffusion of reagent vapor was much faster along the longitudinal direction than along the tangential direction. When the end surface was exposed to the reagent vapor for 48?h, 20% WPG, which was known to have sufficient stability and durability, was achieved to a depth of 42.5?mm. However, this depth was only 6.5?mm when the straight-grain surface was exposed. The reaction profiles were successfully approximated using reaction time (t), reaction rate (k′), delay time (t _d′), and a parameter n reflecting the diffusion-controlled reaction. The t _d′ value increased almost linearly as the depth increased from the surface. The k′ value ranged from 0.02 to 0.03?h^?1, regardless of the depth and direction of diffusion. The n value decreased with an increase in the depth and approached 1–2. These values enabled the prediction of the degree of acetylation at any reaction time and positions of wood during vapor-phase acetylation.     

Enzymic isolation of lignin from wood and pulps

After enzymic hydrolysis of polysaccharides in milled wood or pulp the unhydrolysed lignin residue becomes soluble in certain polar solvents. Extensive disintegration of the wood is necessary to obtain a sufficient accessibility toward the enzyme. For milling a porcelain rotary ball mill is recommended. A relationship has been found between the milling energy, which is proportional to the size of the mill, the milling time, and the yield of ball-milled wood lignin (BMWL). Enzymatically isolated lignin (EIL) requires a critical milling time which is shorter than that for obtaining maximum yields of BMWL. A procedure for isolation of the total lignin content from wood and pulps in the form of three fractions has been developed, giving a water soluble, low molecular carbohydrate-lignin complex by water extraction of ball-milled wood, a BMWL-carbohydrate complex by subsequent extraction with dioxane, and a EIL-carbohydrate complex by dioxane extraction of the residue after enzymic hydrolysis.     

A novel method of acetylation of wood using supercritical carbon dioxide

Sugi heartwood was acetylated with acetic anhydride in supercritical carbon dioxide (CO₂) (120°C or 130°C, 10–12 MPa). As a result, the weight percent gain increased with increasing acetylation time up to 16%–20% at 1 h and 24%–28% at 24 h. The antiswelling efficiency of the acetylated specimens reached 75%–80% at 3–4 h of acetylation. It is supposed that the acetylation in supercritical CO₂ has a high bulking effect compared with liquid-phase and vapor-phase acetylation with uncatalyzed acetic anhydride. The results showed that the acetylation progressed rapidly because supercritical CO₂ and acetic anhydride formed a single phase at more than 90°C, and the acetic anhydride reached the reaction sites in the wood quickly.     

Differential calometric analysis of wood and wood components

Summary The prolysis of cellulose, hemicelluloses, lignin preparations, and wood was studied by differential calorimetric analysis (DCA) for the range of 25° to 800° C. The test samples included powdered and filter paper celluloses; hardwood xylan; softwood galactoglucomannans, compression wood galactan, and arabinogalactan; a synthetic (DHP), sulfuric acid, Björkman, Brownell, and cellulase lignins; and unextracted and extracted hardwoods and softwoods. Heats of reaction were determined from the DCA thermal transition areas. Distinct differences were found between the thermograms of each hemicellulose and lignin sample. Although wood species could not be separated thermally, hardwood and softwood thermograms differed because of the hemicellulose degradation pattern.Trade names and company names are included for the benefit of the reader and do not imply any endorsement or preferential treatment of the product by the U.S. Department of Agriculture.Formerly Research Technologist, Forest Products Laboratory, Forest Service, U.S. Department of Agriculture. The Laboratory is maintained at Madison, Wis. 53705, in cooperation with the University of Wisconsin. Present address: The Pennsylvania State University, University Park, Pennsylvania 16802.     

Notes on the spectrophotometric determination of lignin in wood samples

A method developed by Johnson et al. whereby lignin is determined spectrophotometrically was found to yield lignin values which showed variations of up to 10%. The presence of water in, and the freshness of the digestive mixture together with the grade of acetic acid used and the time between dilution and measurement of absorbance were found to affect the reproducibility of the method.     

Analysis of the factors influencing the acetylation rate of wood

Factors influencing the rate of acetylation were examined based on the swelling of wood in the reaction solution and the dimensions of the wood sample. The activation energy of acetylation was also estimated. In a swelling test, it was found that wood swells thoroughly in acetic anhydride even without pyridine above 60°C. Therefore, pyridine may facilitate the acetylation process as a catalyst and not as a swelling agent. The weight gain, x (%), attained at reaction time t (h), for various compositions of acetylation solution or dimensions of wood sample were analyzed by applying an original rate equation [x = a × (1 – e^–kt )^1/n ], where a is the ultimate weight gain (%), k is the rate constant (h^–1), and n is a measure of the hindrance against the diffusion of reagent. The optimum volume fraction of pyridine in the pyridine-catalyzed acetylation was about 0.2. Accompanied by a rise in pyridine content, the reaction showed increased diffusion-controlled behavior. The rate constant, which is not affected by the dimensions of the wood sample, was estimated from which an activation energy of about 130kJ/mol was calculated.     

Chemical structural elucidation of total lignins in woods I: fractionation of the lignin in residual wood meal after extraction of milled wood lignin

Residual wood meal after extraction of milled wood lignin (WMEM) ofEucalyptus globulus was extracted with alkali and LiCl/N,N-Dimethylacetamide (DMAc). These agents dissolve mainly hemicellulose and cellulose, respectively. The extractability of WMEM in alkali solutions was influenced by the degree of swelling of the cellulose. Under good swelling conditions, considerable amounts of cellulose and lignin were extracted with the hemicellulose. Maximum extractability was about 60% of the WMEM under optimum conditions (3 M or 5 M LiOH or 3M NaOH solution). Some portion of cellulose was extracted with LiCl/DMAc at room temperature. Thus, lignin inE. globulus WMEM was divided into three fractions: hemicellulose-lignin fraction, cellulose-lignin fraction, and insoluble-lignin fraction.Part of this work was presented at the 49th annual meeting of the Japan Wood Research Society, Tokyo, April 1999; and at the 50th annual meeting of the Japan Wood Research Society, Kyoto, April 2000     

木材液相乙酰化处理及处理材尺寸稳定性和耐腐性的研究

本文论述了马尾松、白桦和青杨三种木材的液相乙酰化条件及各种乙酰化木材的尺才稳定性和耐菌腐能力。以乙酸酐和二甲苯为处理液,反应的最佳条件是:温度120℃,时间7到11小时,乙酸酑与二甲苯配比1:1。当处理试样的增重到15%时,抗收缩率可达60%以上。增重为11.75—17.98%的不同处理试块,其耐菌腐能力可提高3—34倍。