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June 1, 2005
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The relationship between transverse Young's moduli and cell shapes in coniferous early wood was investigated using cell models constructed by two dimensional power spectrum analysis. The calculated values of tangential Young's modulus qualitatively explained the relationship between experimental values and density as well as the difference in experimental values among species. The calculated values of radial Young's modulus for the species having hexagonal cells agreed well with the experimental values, whereas, for the species having square cells, the calculated values were much larger than the experimental values. This result was ascribed to the fact that the bending moment on the radial cell wall of square cell models was calculated to be small. It is suggested that the asymmetrical shape of real wood cells or the behavior of nodes during ell deformation is an important factor in the mechanism of linear elastic deformation of wood cells.
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June 1, 2005
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It is not definitively known whether or not the production of extracellular hydrogen peroxide (H 2 O 2 ) is a universal characteristic of brown-rot fungi. Cytochemical localization of H 2 O 2 was tested in two brown-rot fungi, Tyromyces palustris and Coniophora puteana , by staining with cerium chloride. Transmission electron microscopy (TEM) showed the deposition of cerium perhydroxide within the fungal hyphae as well as wood cell walls affected by brown-rot fungi. TEM work indicated that extracellular H 2 O 2 was present in brown-rot fungi and that H 2 O 2 from brown-rot fungi diffused into the wood cell walls in the early stages of decay. The present work strongly suggests that H 2 O 2 plays an important role in the early degradation of cellulose by brown-rot fungi. The usefulness of this technique for localizing H 2 O 2 at high resolution with minimal nonspecific deposition is also discussed.
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June 1, 2005
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Preparations of the previously unreported, water-soluble, tetraguanidinium, tetracholine and tetrakisbenzyltrimethylammonium ellagates are outlined. Ellagic acid and these water-soluble salts remove Mg 2+ , Ca 2+ and Mn 2+ ions from dilute aqueous solutions at pH greater than 7. The salts also remove Fe 2+ , Fe 3+ , Co 2+ and Cu 2+ between pH 3 and pH 6. At pH 1 the water-soluble ellagates underwent hydrolysis, resulting in the precipitation of free ellagic acid in preference to the formation of metal-ellagate complexes. These trends were also observed when mixtures of metal ions were applied.
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June 1, 2005
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Barks from the litters of a multiple level Tertiary fossil forest from the Canadian Arctic were chemically examined and compared with coeval Arctic fossil woods. Degradation and diagenesis of the polysaccharides similarly occurred in barks and woods. However, unlike the fossil woods, the loss of polysaccharides led to materials exhibiting a marked cation exchange capacity, which is comparable to what is found for humus, the final product of diagenesis of the forest litter. Dichloromethane extracts from the barks invariably showed the presence of n -alkanes from C14 to C30, and terpenes such as cadalene, calamenene, fichtelite, sandaracopimarane, abietatriene, simonellite, diaromatic totarane, ferruginol, dehydroferruginol, and sugiol. The presence of phenol-diterpenes and/or diaromatic totarane was related to species belonging to Cupressaceae, Taxodiaceae and Podocarpaceae, in agreement with the recovery of trunks of metasequoia in some forest levels.
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June 1, 2005
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The low field 1 H NMR relaxometry technique has been shown to be effective in determining the qualitative and quantitative moisture content and the water state distribution in maritime pine wood ( Pinus pinaster Ait). Further investigations on extractive materials in resin-rich samples evinced the presence of oleoresin components, which may disturb adhesion on pine wood boards.
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June 1, 2005
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Wastes from industrial processes which use lignocellulosic materials as raw material are an interesting source of chemicals since they can be transformed into products of high added value. In the process described here, ozone was used to produce oxyaromatics from a lignin-rich industrial waste resulting from the production of furfural from almond shells. Ozonation, thioacidolysis and mild alkaline hydrolysis were used to determine some structural features of the raw and acid-hydrolyzed almond shell lignins. During ozone treatment of the different lignin solutions the following compounds were identified: glycolic, oxalic, malonic, glyceric (trace), malic, p -hydroxybenzoic and vanillic acids, p -hydroxybenzaldehyde, vanillin, syringaldehyde and hydroquinone. The aromatic aldehydes passed through a production maximum during the first few minutes of the reaction, while glycolic and oxalic acid (the main aliphatic acids) yields increased throughout the treatment. Raw almond shell lignin had a typical hardwood composition [made up of guaiacyl (G) and syringyl (S) phenylpropane units] and few β-O-4 structures. Acid-hydrolyzed almond shell lignins had a more condensed structure than the above. The S/G ratio obtained by ozonation was slightly lower than that obtained by thioacidolysis, with the (S/G) Ozonation /(S/G) Thioacidolysis ratio ranging from 0.52 to 0.70. The almond shell lignin-polysaccharide complex did not contain any cell wall-esterified p -hydroxycinnamic acid ( p -coumaric and ferulic acids).
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June 1, 2005
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The reaction of two silylating agents (TMSIM, TMS-acetamide) on softwood (white fir) and hardwood (beech) is examined. As proved by means of FTIR microscopy, silylation takes place at the outer surface as well as the inner surface. The FTIR spectroscopical features of both softwood and hardwood remain unchanged. Scanning electron microscopy provides additional evidence that the inner surface is also successfully silylated. Furthermore, the anatomical characteristics of the silylated wood species are not changed. No inorganic elements except silicon could be detected in the EDX-analysis. By means of transmission electron microscopy the reaction site was determined to be on the lumen-faced side of the cell wall. Half of the S2 wall appears to be silylated.
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June 1, 2005
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Guaiacyl-type lignin is the major component of ginkgo lignin. Specific 13 c-enrichment of α, β and γ-carbons of the guaiacylpropane side chains was achieved by administration of coniferin-[α 13 C], coniferin-[β- 13 C] and coniferin-[γ 13 C], respectively, to growing stems of ginkgo trees. Unenriched coniferin was administered as a control. The xylem tissues containing specifically 13 C-enriched lignins or unenriched lignin were subjected to analysis by solid state NMR. Subtraction of the spectrum of tissue containing unenriched lignin from the spectra of tissues containing 13 C-enriched lignins gave difference spectra exclusively assigned to the enriched side chain carbons of intact protolignin in the cell walls. From the signal intensities determined under quantitative conditions and an estimate of corresponding standard uncertainties, the percentage ranges of the major inter-unit lignin bonds originating from the β-carbon of the coniferin precursor were estimated to be: β-O-4/α-O-R (R = H, polysaccharides or lignols) including β-OH, 53% to 57%; combined β-5, β-β and β-1, 32% to 36%; coniferaldehyde end groups, 2% to 4%; and coniferyl alcohol end groups, 4% to 6%.
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June 1, 2005
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The present paper aims at elucidating the effect of high-temperature defibration at different temperatures on the bulk and surface chemical properties of defibrated birch, aspen and eucalypt. The results indicate that defibration of these hardwoods results in partial depolymerization of fiber lignin via (homolytic) cleavage of interunit alkyl-aryl (β-O-4) ether bonds. This increases the phenolic hydroxyl content and produces relatively stable (phenoxy) radicals. Syringyl-type lignin is more extensively depolymerized than guaiacyl-type lignin. Defibration generates water-extractable material, which is enriched in hemicellulose-derived carbohydrates and has a substantial content of aromatic compounds rich in phenolic hydroxyl groups. The amount of water-extract and the extent of lignin interunit ether bond cleavage increase with an increase in defibration temperature. The differences between various hardwood species in this respect are small. The surface chemical composition of the fibers differs considerably from their bulk composition, but is not significantly influenced by variations in defibration temperature. Lipophilic extractives cover a large portion of the fiber surface, while the lignin content of lipophilic extractives-free fiber surfaces is 2–3 times as high as the bulk lignin content of the fibers.
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June 1, 2005
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Eucalyptus globulus wood samples were delignified in two-stage treatments carried out in media made up of formic acid, water and hydrogen peroxide under selected operational conditions. The pulps were subjected to Totally Chlorine Free (TCF) bleaching sequences. Alkaline treatments, oxygen delignification, ozone stages and treatments with peroxyacids were assayed in order to reach the target values for dissolving pulps. Under the best conditions, a fully bleached pulp (91.6% ISO brightness) with SCAN viscosity of 649 ml/g and favourable molar mass distribution was obtained.
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June 1, 2005
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Nonphenolic β-0-4 erythro and threo lignin model diastereomers with various γ-groups (CH 3 , CH 2 -O-CH 3 , and CH 2 OH) and C α -substituents (OH, OCH 3 ) were synthesized, and the alkaline hydrolysis rates and activation parameters determined. In addition, two of the diastereomer pairs were computationally modeled and the thermodynamic values for the ionization of the α- or γ-hydroxyl, and subsequent displacement of the phenolate group to form an epoxide intermediate, were determined. The results suggest that the erythro γ-hydroxyl may participate in the hydrolysis to a significant extent, which results in a relatively high erythro / threo rate ratio for the α,γ-di-OH isomers. The influence of the erythro γ-hydroxyl on the hydrolysis rate may be due to the relatively favorable stability of the erythro γ-oxyanion. The electronic effect of the g-substituent appears to influence how fast the α-hydroxyl displaces the phenoxyl. We had previously suggested that the γ-substituent sterically inhibits hydrolysis of the threo isomer, and computational modeling confirmed this.
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June 1, 2005
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June 1, 2005
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The oxidation of pine kraft lignin by alkaline hydrogen peroxide and cyanamide activated hydrogen peroxide was studied. Over 70% of the kraft lignin was degraded and solublized in the presence of cyanamide as compared to less than 20% by hydrogen peroxide alone. A large decrease in the phenolic hydroxyl and methoxyl content,as well as an increase in the carboxylic acid content was also observed in the insoluble residue. Analyses of the low molecular weight degradation products revealed extensive oxidation of the kraft lignin had occurred,consistent with the ring-opening reactions observed in our previous studies using lignin model compounds.
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June 1, 2005
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The kinetics of ASAM and kraft pulping of eucalypt wood ( Eucalyptus globulus ) were studied in relation to delignification and polysaccharide removal. In comparison to kraft, ASAM pulping had lower mass losses and delignification for the same temperature and reaction times (59.2% at Kappa 25 vs 50.0% at Kappa 17, at 180°C). The ASAM pulps have a higher brightness. ASAM pulping had a short initial period with no mass loss and lignin removal, followed by two reaction phases: a main phase where 61% of lignin was removed (at 180°C) and a subsequent final phase. In comparison to kraft, the main delignification rates of ASAM pulping were approximately 2.5 slower (at 180°C, −1.8 × 10 −2 min −1 for ASAM and −4.2 × 10 −2 for kraft pulping), and the calculated Arrhenius activation energies were higher (132.4 kJ mol −1 and 83.5 kJ mol −1 , respectively). The loss of cellulose was relatively small (12.5 %) and lower than in kraft pulps.
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June 1, 2005
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To understand the swelling phenomenon of wood in liquids,the saturated amount of adsorption of liquids onto wood and the standard free energy changes of the adsorption were determined. The saturated amount of adsorption obtained by regression for several liquids decreased with increasing molecular size of the solvents. The mechanism of wood swelling is discussed systematically taking all the liquids examined in previous experiments into account. Since methanol molecules require more energy for release from cohesive interactions within bulk liquids in the adsorption onto pre-swollen wood,the values of free energy change of adsorption for methanol were lower than the values for acetone,although the relative swelling with methanol was higher. These results suggest that although the cohesive interaction within the bulk liquids reduces adsorptivity,the phenomenon of wood swelling is influenced not only by monolayer adsorption but also by multilayer adsorption. Therefore,the cohesive interaction within the bulk liquids reduces adsorptivity but enhances the condensation which strongly influences the swelling of wood.
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June 1, 2005
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To clarify tangential and radial dimensional changes in hinoki ( Chamaecyparis obtusa ) wood by ten kinds of treatments and successive water soaking, a vector expression on the tangential-radial coordinates was proposed and a new measure (ASE′) to evaluate the dimensional stability of wood was defined. The ASE′ is expressed by 100(1 − V s′ / V u ) where V u is the volumetric swelling coefficient of untreated wood and V s′ is that of treated wood calculated on the basis of its oven-dried volume before treatment. The results from formaldehyde treated, heat treated and steam treated wood showed large positive ASE′ values and the ratio of radial swelling to tangential swelling (swelling anisotropy) of these treated woods decreased with increasing weight percent gain or weight loss. The results from acetylated wood, wood impregnated with polyethylene glycol and wood treated with a low molecular weight phenol-formaldehyde resin showed either small positive or negative ASE′ values, and those of wood treated with propylene oxide showed large negative values. The swelling anisotropy of treated woods accompanied by cell wall bulking was larger than that of untreated wood. The swelling anisotropy decreased when the cell lumen was filled with a hydrophobic resin (WPC-MMA), and increased when the cell lumen was filled with a hydrophilic resin (WPC-HEMA).
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June 1, 2005
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Using UV-microscopy, absorbance spectra of a cured melamine-urea-formaldehyde resin and secondary cell walls of spruce wood glued with this resin were determined. Analysis of the spectra showed that peaks characteristic for both coniferous lignin and melamine resin were present in cell walls of tracheids embedded in the resin. A quantitative estimate indicated a melamine content of the resin embedded cell walls of 6.2%. It could be demonstrated that UV-microscopy is well suited for the investigation of resin diffusion into the wood cell wall.
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June 1, 2005
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The indoor environment can constitute a serious health hazard if buildings are not properly constructed and finished. Building, finishing and furnishing materials may emit a large number of volatile organic compounds (VOCs) into the indoor air. That wood-composite products are among the sources of formaldehyde emissions is well documented. Up until now very little has been known about the emission of VOCs from wood-composite products (Merrill and Steiber 1987; Levin 1992; Sundin and Edenholm 1992; Catananti et al. 1993; Barry and Corneau 1999). The aim of this work is the determination of VOC and formaldehyde emissions from particleboard veneered with decorative paper foil.
