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October 7, 2005
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October 7, 2005
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October 7, 2005
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October 7, 2005
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June 1, 2005
Abstract
This paper describes the effect of light on the diurnal change in the innermost surface of developing secondary walls. Cryptomeria japonica D. Don saplings were grown in two growth chambers, in which temperature and relative humidity were kept constant and the light-dark phase of the photoperiod varied. One chamber reproduced the natural light-dark phase, while the other reversed it. Samples of differentiating xylem were collected during the dark period when the tangential strain, used as an index of volumetric changes in differentiating cells, was high, and during the light period when the tangential strain was low. The innermost surface of developing secondary walls in differentiating tracheids was observed by field emission scanning electron microscopy. In the specimens collected during the dark period, amorphous material was observed and the cell wall surface was immunogold-labeled with an anti-glucomannan antiserum. In the specimens collected during the light period, cellulose microfibrils were clearly evident, and amorphous material and immunogold labeling were rarely observed. These results demonstrate that the diurnal changes in the innermost surface of developing secondary walls correspond to the light-dark cycle over 24 h.
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June 1, 2005
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New Trichoderma isolates were prepared from soils collected in the areas of the world where the dry rot fungus Serpula lacrymans is indigenous. Agar-screening tests were carried out to identify the antagonistic effects of isolates and determine if their mode of action was geared towards production of volatiles. Overall, Trichoderma isolates from Northern California, USA, were found to be extremely effective against S. lacrymans (Schumacher ex Fr. Gray.) and some produced a killing effect in the agar systems. In addition, these isolates inhibited S. lacrymans growth by volatile production even in the absence of direct contact between the Trichoderma isolate and S. lacrymans , whereas a standard laboratory culture of Trichoderma harzianum T25 was found to be much less effective. In two different soil and wood microcosms the USA isolates were also able to stop the growth of S. lacrymans and produced an apparent killing effect.
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June 1, 2005
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June 1, 2005
Abstract
The termiticidal performance of wood-based composites [medium density fiberboard (MDF), hardwood plywood, softwood plywood, particleboard and oriented strand board (OSB)] was evaluated following treatment with a non-ester pyrethroid, silafluofen, using supercritical carbon dioxide (SC-CO 2 ) as a carrier solvent. Treatment was conducted under nine combinations of temperature (35°C, 45°C or 55°C) and pressure [7.85 MPa (80 kgf/cm 2 ), 9.81 MPa (100 kgf/cm 2 ) or 11.77 MPa (120 kgf/cm 2 )]. Treated and untreated samples were individually exposed to the subterranean termite Coptotermes formosanus Shiraki in the laboratory, and the percent mass loss of the samples and termite mortality were determined to compare the termiticidal performance among the wood-based composites and treatment conditions. Silafluofen/SC-CO 2 treatment significantly improved the termite resistance of all of the wood-based composites, although the termiticidal performance varied with the composite type and treatment conditions. The best performance for MDF, hardwood plywood, softwood plywood and particleboard was obtained at 35°C-7.85 MPa in terms of the inhibition of feeding, and gave high termite mortality and energy-conservation, whereas the best performance for OSB was at 35°C and 9.81 MPa or 11.77 MPa.
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June 1, 2005
Abstract
The concept of animal protein utilization aiming to reduce leaching of treatment salts from wood was tested and verified. Animal proteins in the form of spray-dried animal blood plasma were used as an addition to the water solution of fungicidal salt or included in the solution for soaking pre-treated wood. The wood was subjected to thermal treatment which caused protein denaturation, a process which changes the proteins' spatial conformation and reduces their solubility in water. Scots pine wood ( Pinus sylvestris L.) was treated with a water solution of copper sulfate using vacuum, vacuum-soaking and vacuum-pressure methods. The animal proteins were added to the treatment solutions or applied by soaking to samples pre-treated with the salt. After treatment, the samples were heated to 100°C. After suitable conditioning, the wood was subjected to leaching. The content of Cu 2+ in the water extracts was determined by Atomic Absorption Spectrophotometry (AAS).
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June 1, 2005
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Considerable research has been conducted to quantify the leaching rates of chromium and arsenic from timbers treated with the traditional wood preservative, CCA. However, much of this work has concentrated on measuring total metal concentrations. The environmental toxicity of these elements is significantly affected by their oxidation state. Therefore, quantification of individual metal species is considered important if the environmental effects of wood preservative leachates are to be determined. Laboratory leaching tests were conducted to allow speciation of both chromium and arsenic lost from CCA treated timbers exposed to artificial seawater for the first time. Differential pulse polarography was used to measure concentrations of As(III), Cr(VI) and Cr(III). Analysis indicated that less than 10% of the total As was leached as As(III), and that less than 1% of the total Cr was leached as Cr(VI).
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June 1, 2005
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Milled wood lignin as well as wood meal from todo fir ( Abies sachalinensis MAST) was treated with 70% aqueous 1,4-butanediol solution at 220°C without acid catalyst in order to elucidate the delignification mechanism during high-boiling solvent (HBS) pulping. HBS lignin was recovered from black liquor by precipitation, and was subjected to gel permeation chromatography and quantitative 13 C-NMR study. The average molecular weight of MWL decreased. The content of phenolic hydroxyl groups in MWL increased from 0.28 to 0.68/OMe. The decrease in the content of β-O -4 substructures was evident, which may be attributed to the homolytic cleavage of phenolic β -aryl ethers. The changes in the content of β -5 and β-β substructures were rather small. The benzyl ether formation of β-O -4 structures with 1,4-butanediol was also confirmed by 13 C-NMR. However, the signals corresponding to Hibbert's ketones were not observed, which suggests that acidolysis was not an important degradation pathway during HBS pulping.
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June 1, 2005
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Delignification of spruce ( Picea abies [L.] Karst.) during ASA (modified alkaline sulfite/anthraquinone pulping with alkali splitting) and magnesium bisulfite pulping was studied on a cellular level using scanning UV microspectrophotometry. This improved cellular analytical technique enables direct imaging of the topochemistry of lignin removal within the cell wall at different stages of cooking. The cooks were performed in a laboratory digester with forced liquor circulation. At 30 min intervals samples were taken for chemical and UV microscopic analyses. UV microscopy reveals that delignification during ASA pulping starts in the region of the pit canals and proceeds evenly across the entire S2 layer. As a specific feature of bisulfite pulping, a partial delignification of the radial compound middle lamella can be detected after 60 min of cooking. After 120 min, in both processes, the delignified cell walls show low UV absorbance values of both S2 and compound middle lamella. At this stage, approximately 90% of the initial lignin content is removed. At the end of both pulping processes, only parts of the cell corners can be distinguished by the new UV scanning technique.
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June 1, 2005
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Bamboo ( Bambusa procera acher ) was delignified in a laboratory-scale digester by conventional kraft pulping under varying conditions. Pulps with kappa numbers in the range 12.9–56.3 and viscosities in the range 871–1319 ml g −1 were obtained. The chemical composition of the corresponding black liquors was analysed with respect to their main organic and inorganic constituents. The results indicated that the dry solids of the black liquor contained 40–44% lignin, 20–24% aliphatic carboxylic acids, 4–7% polysaccharides and the residual matter (about 30%) consisted mainly of inorganic constituents. Of the monosaccharide moieties detected in the polysaccharides, xylose was predominant, suggesting that xylan was a major hemicellulose constituent in the black liquor. The effect of effective alkali, sulphidity and H-factor of the cook on the formation of the individual constituents in the black liquor is also discussed.
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June 1, 2005
Abstract
We recently reported that during peroxide bleaching, magnesium is substantially more effective when in a complex form with either pulp or a chelant. We also speculated that different magnesium forms affected the catalytic activity of transition metals towards peroxide decomposition to different degrees. As oxygen-delignified pulps still containing lignin were used, it was impossible to separate the catalytic peroxide decomposition by transition metals from the peroxide reaction with lignin, and thus to determine where in the pulp-liquor system magnesium or chelants, or both, were deactivating transition metals. In this paper, we studied the peroxide decomposition kinetics with different modes of addition of the P-stage chemicals in the presence of fully-bleached kraft pulps which are virtually lignin-free, in alkaline filtrates, in P-stage filtrate and in water. We found that most of the peroxide decomposition occurring during a P-stage applied to chemical pulps takes place through interaction with transition metals in the pulp rather than with transition metals in the soluble bulk phase. We also concluded that in any component of a peroxide bleaching system, magnesium is extremely efficient at reducing the rate of peroxide decomposition, while a chelant becomes more valuable when complexing magnesium.
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June 1, 2005
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Changes in the moisture content of green sitka spruce ( Picea sitchensis Carr.) during heating in environments of over 100°C and 1 atm were measured. Temperature and weight were measured in a highly accelerated stress test (HAST) chamber. The set temperature and relative humidity ranges were 107–160°C and 75–99%, respectively. The change in the temperature of a specimen was roughly divided into 4 steps. Equilibrium moisture contents at lower temperatures and pressures were similar to previous estimates, while at higher temperatures and pressures they were higher than previous results. A diagram of temperature–relative humidity–pressure–equilibrium moisture content in the range of 105–160°C, 75–99% RH and 0.02–0.39 MPa was obtained experimentally.
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June 1, 2005
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A research program was conducted to investigate the effect of water transition on wood fracture properties, focusing on fracture behavior and patterns with different crack orientations of Betula platyphylla Suk. and Pinus bungeana in three different moisture adsorption processes. At a constant temperature of 20°C, three levels of relative humidity were considered: 66%, 82% and 100%. The results indicated that moisture content did not influence the crack propagation path, while specimen crack orientation did. With longer moisture adsorption times, the time needed to reach the maximum load from the critical load also grew; this is because below the fiber saturation point, from excessive dryness to a certain moisture content, the cell wall becomes less brittle and the toughness is enhanced. At 20°C constant temperature, the fracture toughness gradually increased from oven-dry state adsorbing moisture to 82% relative humidity, but decreased from 82% to 100% relative humidity. Within a tree species, fracture toughness depended on specimen type. The fracture toughness of LT specimens was by far higher than that of TL and TR specimens. The LT specimen fracture toughness of Betula platyphylla Suk. was comparable to that of Pinus bungeana .
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June 1, 2005
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This study develops a high performance grading process based on the analysis of acoustic vibrations in the audible frequency range. The unique feature of the method is that the spectrum is directly applied to obtain predictive variables for estimating the modulus of elasticity and modulus of rupture. A partial least squares regression was used. This powerful method represents a compromise between principal component regression and multi-linear regression. Partial least squares regression screens for factors which account for the variance in the predictor variables and achieves the best correlation between factors and predicted variable. The method is based on projections, similar to principle components regression, whereby a set of correlated variables is compressed into a smaller set of uncorrelated factors.
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June 1, 2005
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Crack propagation in wood is strongly influenced by the microscopic structure of the material. The relationship between structure and function with regard to damage and fracture behaviour can only be understood with a sufficiently fine level of examination. An experimental approach to perform micro-wedge splitting tests on spruce and beech inside the chamber of an Environmental Scanning Electron Microscope and under atmospheric conditions is presented. The specimens are loaded in mode I in the TR crack propagation system. Based on the load-displacement diagram, the characteristic parameters of fracture energy, critical load and initial elasticity are determined. The load and displacement data for the in situ experiments are related to the obtained ESEM images and allow a discussion of the fracture process on the cellular level. Density was found to be an important factor for fracture mode and several crack arresting phenomena depending on the variation of elasticity could be identified.
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June 1, 2005
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June 1, 2005
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A method for measuring shrinkage resulting from drying in the three anisotropic directions is developed and tested. Measurements are performed on sawn discs, a technique which simplifies preparation and enables large numbers of measurements. Shrinkage values can be represented as a map of the disc surface. The results indicate that comparisons between shrinkage distribution and tension wood distribution on the discs show a clear relationship and can be measured with relatively high accuracy in reference to the “shrinkage map”. In the long term, this method could be useful in the timber industry as a means for choosing the direction in which logs are cut depending on their type of wood composition.
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June 1, 2005
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The influence of wood upon the setting of cement is generally assessed by conducting semi-adiabatic hydration tests. The existing methods to quantify wood-cement compatibility are based on the maximum hydration temperature ( T max ), the time ( t max ) to reach it or the heat evolved in a specified period. Results obtained by these methods at higher wood-cement ratios are not convincing and show inconsistencies for various reasons. This paper discusses these reasons and suggests an alternative method based on a maturity function. The results from the new calculation method are compared with those of the existing methods and demonstrate the superiority of this new method at higher wood-cement ratios.
