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January 17, 2006
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To better understand the within-tree variations between juvenile wood, mature wood, and compression wood, wood from a 35-year-old mature bent loblolly pine was separated into seven groups by different positions in the tree. Morphological and chemical structure analyses, including fiber quality, X-ray diffraction, sugar and lignin content analysis, as well as nitrobenzene oxidation, ozonation, and advanced NMR spectroscopy, were performed. Fiber properties were significantly different for tree-top juvenile normal wood and tree-bottom juvenile normal wood, juvenile normal and mature normal wood, juvenile compression and mature compression wood. However, differences in the chemical structure and composition were less significant within the specific tissues indicated above.
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January 17, 2006
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In this study the rate and extent of mercury incorporation into different morphological fractions, i.e., fibers, mechanically peeled fibers, primary and secondary fines, of an unbleached softwood kraft pulp were evaluated. In addition, the surface coverage of the different morphological pulp fractions by lignin was quantified using XPS in combination with mercurization. Incorporation of approximately one mole of mercury per mole of lignin (C 9 -unit) was obtained for the different morphological parts after a 10-h reaction. Extractives inhibit the mercurization reaction; however, this effect decreases as the mercurization procedure proceeds and disappears after approximately 10 h. XPS analysis showed that the amount of lignin on the pulp fiber surfaces was approximately twice as high as in the rest of the fibers and that mechanical peeling in a disintegrator removed lignin-rich material from fiber surfaces. The amount of surface lignin on primary and secondary fines was 3.5- and 6.5-fold higher than in the bulk, respectively. The mercurization technique in combination with XPS is well suited for verification of the amount of surface lignin.
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January 17, 2006
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Three different XPS methods based on the O/C atomic ratio, C1 carbon content, and Hg amount are compared in this study to quantify the surface coverage of various pulp fiber surfaces by lignin and extractives. The sensitivity of the methods to drying technique and the stability of organically bound mercury when subjected to X-ray irradiation were also investigated. Results reveal that the surfaces of all pulp fibers have a higher content of lignin and extractives than the bulk of the fibers. Similar lignin surface coverage was obtained for thermomechanical pulp fibers using the Hg, O/C, and C1 carbon methods, while the Hg method gave lower values for kraft pulp fibers than the O/C and C1 carbon methods. The O/C and C1 carbon methods are sensitive to the drying technique, i.e., air-dried samples showed a higher amount of lignin on the fiber surface than freeze-dried samples, while no or only minor differences in results were obtained using the Hg method. The Hg method was more reproducible than the other methods. Special care must be exercised during XPS analysis to minimize mercury degradation.
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January 17, 2006
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Bioassay-guided isolation of compounds from n- hexane extracts of the bark of Cryptomeria japonica resulted in six abietane- and two pimarane-type diterpenoids, including a new compound, 12-methoxy-6α,11-dihydroxyabieta-8,11,13-triene. The structure of the new substance was established by spectral analyses and comparison with related compounds. The antifungal activities of these diterpenes were evaluated against the phytopathogenic fungi Alternaria alternata , Pyricularia oryzae , Rhizoctonia solani and Fusarium oxysporum . The diterpenes showed moderate antifungal activity against the fungi examined.
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January 17, 2006
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Genetic engineering of trees has generated a large amount of interest in the development of highly improved transgenic trees. To efficiently monitor and control the properties of the transgenic products, a rapid, mini-scale analytical method is required. Transmittance near-infrared (NIR) spectroscopy was chosen as a fast analysis tool for characterizing the chemical properties of the transgenic products. Pellets were prepared from 75 mg of wood meal and directly scanned using transmittance NIR spectroscopy. Very strong correlations were obtained between the NIR data and conventional wet-chemistry results for the lignin content, S/G ratio, cellulose and xylose content. The results indicate that transmittance NIR is a powerful tool for determining and screening the chemical properties of transgenic trees.
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January 17, 2006
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January 17, 2006
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The chemistry of chemithermomechanical pulping (CTMP) was assessed by chemical pre-treatment of spruce chips, followed by laboratory-scale refining. Pre-treatments with alkali, sulfite, alkaline sulfite and alkaline peroxide liquors were carried out at 40°C, 60°C and 80°C. The sodium hydroxide dosages were 1% and 2% and the sodium sulfite and hydrogen peroxide dosages were 2%, 4% and 6% on a dry wood basis. Process water samples were taken before and after refining. Alkali consumption in the pre-treatments and the amount and composition of released wood components were determined. A major part of the alkali was consumed in the alkaline and alkaline sulfite pre-treatments. In the alkaline peroxide pre-treatments, however, alkali consumption was considerably lower. Acetic acid was the main wood component released to the process waters in alkaline pre-treatments. Pectins, determined as galacturonic acid and rhamnose by acid methanolysis, were also released to some extent, as well as easily soluble polysaccharides. After fibre separation in refining, more hemicelluloses and pectins were released. There was a significant difference between the degree of demethylation for pectins and the degree of deacetylation for galactoglucomannans after the pre-treatments. The diffusion of chemicals into the secondary wall layers seemed to be slower than the liquor penetration into the porous middle lamella through the pit pores. Up to 10% of the pectins were dissolved in the process waters as a result of depolymerisation and extensive demethylation. The residual amount of pectins in the fibres, however, was determined to be as low as 65–70% of the initial pectin content.
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January 17, 2006
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Three types of silanes were tested for their ability to impart hydrophobicity to solid wood samples: a tetraalkoxy silane bearing four hydrolysable alkoxy groups; two alkyl-trialkoxy silanes; and two multifunctional oligomeric silane systems. The first two types were applied as monomeric silane solutions and pre-condensed sols. The water uptake of treated wood was considerably reduced, especially after treatment with multifunctional water-borne silane systems, while uptake of gaseous water was not changed. Initial water repellence was most pronounced when a fluoro-alkyl functional oligomeric silane system was used; however, after a longer submersion time (24 h), the reduction in water uptake was strongly diminished. Wetting-drying cycles led to a reduction in hydrophobicity of samples treated with sols of alkoxysilanes, while aqueous functional silanes revealed enhanced water-repellent effects after these tests. This was explained by continued condensation of unreacted silanol groups in the aqueous functional silanes during the wetting-drying cycles. X-Ray mapping of silicon (SEM-EDX) showed that the reduction in water uptake due to the multifunctional silane HS 2909 is caused by plugging of the main penetration pathways such as pits, ray cells and ray tracheids.
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January 17, 2006
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Parallel-plate rheological analysis was conducted on two types of cross-linking poly(vinyl acetate) latex films: dry freestanding films, and dry films bonded directly to wood (composites). For each sample type, three levels of cross-linking were used: (1) little or no cross-linking of unaltered latex; (2) substantial cross-linking through AlCl 3 catalysis of N -methylolacrylamide co-monomer; and (3) greater cross-linking from a phenol-formaldehyde resol additive, in addition to AlCl 3 catalysis. Simple thermal scans revealed a strong wood/adhesive interaction; wood increased the base polymer T g by ∼5°C in all adhesives. Relative to the simple thermal scans, time-temperature master curves provided more insight and information about the wood/adhesive interaction. Storage modulus and tan δ master curves both indicated that wood retarded adhesive cross-linking. Using time-temperature superposition, a segmental coupling analysis demonstrated that wood actually narrowed the breadth of the glass transition, or reduced segmental coupling. Cross-linking influenced segmental coupling, but in a fashion that was dependent on the presence or absence of wood. Wood-induced reductions in cross-linking and in segmental coupling were attributed to the diffusion of water-soluble reactive compounds away from the adhesive layer and into the bulk wood. Time/temperature equivalence provides a sensitive means to detect interactions between wood and viscoelastic adhesives.
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January 17, 2006
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In this study, the reinforcing potential of cellulose “microfibres” obtained from bleached softwood kraft pulp was demonstrated in a matrix of polyvinyl alcohol (PVA). Microfibres are defined as fibres of cellulose of 0.1–1 μm in diameter, with a corresponding minimum length of 5–50 μm. Films cast with these microfibres in PVA showed a doubling of tensile strength and a 2.5-fold increase in stiffness with 5% microfibre loading. The theoretical stiffness of a microfibre was calculated as 69 GPa. The study also demonstrated that the strength of the composite was greater at 5% microfibre loading compared to 10% loading. Comparative studies with microcrystalline cellulose showed that the minimum aspect ratio of the reinforcing agent is more criticalthan its crystallinity in providing reinforcement in the composite.
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January 17, 2006
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The diffusion rate of tritiated water into pine and aspen particles follows a Fickian mechanism. The tortuosity for the diffusion of water into wood is quite low, at approximately 1.6, and increases with decreasing particle size. The tortuosity for aspen is higher than that for pine because the shorter fiber structure in aspen gives rise to a more extensive network of pores. Diffusion into free and bound water occurs at the same rate. Also, diffusion into and out of the particles is nearly identical, demonstrating that diffusion of water into saturated wood particles is completely reversible. No hysteresis was evident, in contrast to behavior for water adsorption on unsaturated wood. The implications of these findings for pulping and wood drying are discussed.
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January 17, 2006
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Thermal modification processes improve the durability and dimensional stability of wood, but strength properties, especially dynamic ones, are compromised. Results from standard dynamic strength testing, such as impact bending tests, suffer from high variability and therefore require a high number of replicates. To overcome this, a new test method named high-energy multiple impact (HEMI) was developed by investigating heat-treated Picea abies Karst., Abies alba Mill. and untreated Robinia pseudoacacia L. The method is based on crushing small specimens by thousands of impacts from pounding steel balls in a heavy vibratory mill. The level of destruction was determined by sieving and analyzing the size distribution of the fragments. We calculated the resistance to impact milling (RIM) based on the mass of the size fractions. RIM shows a linear correlation with the intensity of the thermal treatment. The HEMI test method has the following advantages: small number of specimens, short time for specimen preparation, small variances, and high reproducibility of results.
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January 17, 2006
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For many applications, the perceived quality of a medium-density fibreboard (MDF) is influenced by the appearance of its machined surface. The behaviour of MDF has been studied by passing a cutting tool through it at a relatively low speed. A digital camera was used that travels synchronously with the tool and the deformation occurring in front of the tool tip was recorded. The magnification of approximately 30× also allows the individual fibres or bundles to be clearly observed. Photographic images have also been taken of the same machining process at a much higher speed, producing similar results and thus establishing the slow-speed study as a viable option. The machining of different MDF samples has been recorded using a cutting speed of 1.6 mm s −1 and varying depths of cut (0.5, 0.75 and 1.0 mm). The video recordings of various panels permit the identification of their peculiar machining characteristics. Unrefined particles play a major role during machining. The trends of results have also been confirmed by scanning electron micrographs. The board densities were found to have a major influence on the machinability characteristics of the boards.
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January 17, 2006
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Modal analysis was used to determine the rolling shear modulus of Norway spruce samples that were either untreated or inoculated with fungi. The resonance frequencies of centimeter-range cuboids were measured using contact-less laser interferometry. A three-dimensional theoretical model describing the orthotropic behavior of the material was used to calculate the resonance frequencies. Using an iterative scheme based on the least-squares method, the value of the rolling shear modulus was then extracted. In this first investigation, the decrease in the rolling shear modulus and the weight loss of Norway spruce inoculated with white-rot fungi Heterobasidion annosum and Ganoderma lipsiense were studied for three different exposure times ranging from 4 to 12 weeks. Comparison of measured and theoretical resonance frequencies confirmed that operation was in the applicable range of the theoretical model for the inoculated specimens. A decrease in rolling shear modulus of up to 10% ( H. annosum ) and 50% ( G. lipsiense ) was found.
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January 17, 2006
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Samples of maple were pyrolyzed and subsequently activated by carbon dioxide at different temperatures for various dwell times. The changes in wood structure were characterized by nitrogen adsorption isotherms, transmission electron microscopy (TEM) with selected-area electron diffraction (SAED), and scanning electron microscopy (SEM). Increasing pyrolysis temperatures promoted increased crystallization of graphitic wood components and mineral-like phases. The average pore diameter derived from nitrogen adsorption isotherms approximately correlated with the results obtained by high-resolution SEM and TEM. The highest surface area was found for samples containing considerable amounts of nanoperforated pit membranes located in intervascular pitting. High-resolution TEM examinations of membrane regions showed foam-like clusters with an average size of 1.7 nm, which are attributed to the selective influence of CO 2 activation on pyrolyzed cellulose and lignin.
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January 1, 2006
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Discolouration of wood raw material during wet storage has a notable negative effect on the quality of the final product. In this study, fluorescence microscopy was used to investigate the spatial distribution of discolouring substances in water-sprinkled Norway spruce pulpwood. Water-sprinkled wood was characterised by the presence of discolouring substances on the pit membranes of wood cells. In vitro model studies on the interaction between a model bark substance (tannic acid) and torus constituents support the hypothesis that pectic structures facilitate the allocation of bark substances on pit membranes. Applied pectinase or tannase could not remove the discolouring substances from pit membranes. Manganese peroxidase had a minor but documented effect. The effect of manganese peroxidase, as well as HCl/vanillin labelling, indicated that the discolouring substance may be condensed tannins.
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January 1, 2006
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The aim of this study was to find chemical or physical properties of Siberian larch heartwood timber that correlate with the variation in decay resistance. Juvenile heartwood from 24-year-old grafts of 15 clones was exposed to three brown-rot fungi according to the standard in vitro decay test (European standard EN 113). The mass losses caused by the brown rot fungi Coniophora puteana , Poria placenta , and Gloeophyllum trabeum were 20%, 28% and 17% of the dry mass, respectively. The average mass loss over the three fungi had a strong negative correlation with the concentration of taxifolin (r=–0.673, P=0.006), as well as with the concentration of total phenolics determined by the Folin-Ciocalteu assay (r=–0.677, P=0.006). Thus, the concentration of flavonoids is a promising property for indirect measurement of the decay resistance of Siberian larch timber. The most abundant heartwood extractives, arabinogalactans, had a non-significant relationship with the decay resistance, but their concentration correlated positively with the capacity of the wood to adsorb water (r=0.736, P=0.002). The hygroscopic properties of the wood or the wood density were not associated with the decay resistance.
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January 1, 2006
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Insoluble metaborates were formed by impregnating wood with borax and metallic salts, and the biological resistance of samples treated with metaborates was evaluated. The double-diffusion process was carried out to form metaborate precipitates in sapwood specimens of Japanese cedar ( Cryptomeria japonica ). Water-saturated wood specimens were first impregnated by a saturated borax solution and then diffusion-penetrated with solutions of zinc sulfate or copper sulfate of different concentrations. In laboratory-scale termite tests of wood specimens treated with zinc and copper metaborates at five concentrations from 3% to 20% using a virulent subterranean termite ( Coptotermes formosanus ), metaborate-treated wood showed negligible weight loss, with high termite mortality at the lowest concentration of 3%. An additional termite test for treatments at lower concentrations of 1% and 2% revealed good termite resistance even with small weight gains of 2.3–6.7%. In field termite tests using a tropical dominant termite ( Macrotermes gilvus ) in Serpong, Indonesia, wood specimens of 2 cm (r)×2 cm (t)×10 cm (l) treated with metaborates at 5% and 20% showed little weight loss against termite attack for 2 months or more. In addition, in a decay test using a white-rot fungus ( Trametes versicolor ) and a brown-rot fungus ( Fomitopsis palustris ), metaborate-treated woods showed enhanced decay resistance. This superb enhancement of biological resistance against termite and decay attacks is considered to be attributable to the presence of metaborates containing effective components such as boron, zinc or copper in the cell walls, which were detected by EPMA observations.
