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August 8, 2005
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The present study is dealing with the question how the major yield-controlling components in pulp (i.e.,hemicelluloses and lignin) alter the behavior and/or properties (e.g., dimensions, flexibility, sugar content) of the fibers. The hypothesis should be verified that certain fiber properties can be used as marker for yield information. Pine and maple wood were digested under specific conditions to produce unbleached pulps with two different lignin contents per method. Screened pulps were chemically analyzed using a new NMR technique for carbohydrates, and the fibers were fractionated using a modified Bauer McNett classification. Pulp yields were related to the pulping methods in the sequence: polysulfide>kraft>biokraft>soda. Carbohydrate analysis revealed that the glucose content (glucose method) was related to the pulping yield. Certain fiber properties (fiber width and coarseness measured directly from the screened pulps) also provided close correlations with the pulp yield. The arithmetic average fiber length and width of the R 14 Bauer McNett screen was a significant predictor of yield at the 95% confidence level, with a mean error of 0.43%.
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August 8, 2005
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The chemical characteristics of lignin and extractives on the outermost surface of hardwood rapid displacement heating (RDH) kraft pulp were studied using time-of-flight secondary ion mass spectrometry (ToF-SIMS). Changes in these surface compounds induced by totally chlorine-free (TCF) bleaching were also revealed. The results suggest that the surface lignin remaining on unbleached RDH pulp was remnant from native wood lignin, which was never released from wood fibers, but had undergone structural changes during kraft cooking. Less than half of the surface lignin was removed during bleaching, with the oxygen stage and the final peroxide stage being the most effective. The main wood extractives on the hardwood RDH kraft pulp surface were sterols and steryl esters. TCF bleaching strongly reduced their abundance. Bleaching also removed fatty acids, but less effectively than neutral extractives. Fatty acid sodium salts were partly removed during TCF bleaching, in contrast to fatty acid calcium salts, which were very stable. ToF-SIMS has the unique capability to give valuable chemical information about the complex mixture of compounds on the pulp surfaces. Thus, it complements other surface-sensitive analytical techniques such as electron spectroscopy for chemical analysis (ESCA), atomic force microscopy (AFM) and field-emission scanning electron microscopy (FE-SEM). ToF-SIMS can give detailed chemical information about the effects of process conditions on pulp surface characteristics.
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August 8, 2005
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The composition of mature, juvenile uninfested and juvenile infested Fraser fir wood (Rotholz) and the structures of lignins isolated from these woods were elucidated to verify differences between juvenile and mature wood and the effect of balsam woolly adelgid (BWA) infestation. Milled wood lignin (MWL) isolated from mature, juvenile and Rotholz wood were comprehensively characterized using heteronuclear multiple quantum coherence (HMQC) and quantitative 13 C NMR techniques. The Rotholz wood was found to have ∼13% higher lignin content and more than five-fold the amount of galactans than that of the uninfested wood. Rotholz lignin possesses higher amounts of p- hydroxyphenyl units and aliphatic OH groups and a lower amount of alkyl- O -alkyl linkages and dibenzodioxocin moieties. The degree of condensation of the Rotholz lignin was rather similar to that of normal wood. Only small differences in the structure of mature and juvenile wood components were found.
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August 8, 2005
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Based on their hydrolysis behavior, NMR spectra of the erythro and threo forms of 3-(3,4-dimethoxy-phenyl)-2-(2,6-dimethoxyphenoxy)-3-ethoxypropan-1-ol (named VSE, i.e., α-ethyl ether derivative of veratrylglycerol-β-syringylether) were successfully assigned. A mixture of erythro and threo VSEs was treated at 90°C in pH 1.2 nitric acid solution. In order to assign them, the molar ratios of erythro and threo forms of 1-(3,4-dimethoxyphenyl)-2-(2,6-dimethoxy-phenoxy)propane-1,3-diol (named VS, i.e., veratrylglycerol-β-syringyl) ether given by each VSE were kinetically determined during the treatment. It was found that the inversion ratio at which the first VSE isomer gave erythro -VS was 0.73. Therefore, this isomer was identified as threo -VSE. In addition, from calculations using the least-squares method, the inversion ratio at which the other VSE isomer gave threo -VS was found to be >0.73. These values mean that threo -VSE yields 73% erythro - and 27% threo -VS, while erythro -VSE yields mainly threo -VS.
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August 8, 2005
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N -Methylene(morpholinium) ions (carbenium-iminium ions) are responsible for uncontrollable reactions of Lyocell dopes – solutions of cellulose in N -methylmorpholine- N -oxide monohydrate at process temperatures of approximately 100°C – as they are able to induce autocatalytic decomposition of the solvent. The carbenium-iminium ions derived from N -benzylmorpholine- N -oxide (NBnMO) are less reactive, affording innocent products instead of entering an uncontrollable decomposition pathway. The “dangerous” carbenium-iminium ions derived from NMMO are efficiently scavenged by NBnMO, which is in turn converted into these “innocent” NBnMO-derived carbenium-iminium ions. Color generation in NBnMO-stabilized NMMO is far less pronounced, than in the case of the traditionally used phenolic anti-oxidant stabilizers. This suggests that NBnMO could be used in a novel approach to stabilize Lyocell solutions.
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August 8, 2005
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The decomposition mechanism of peracetic acid by free Mn 2+ ions and by Mn 2+ -diethylenetriaminepentaacetic acid complexes was studied by UV/Vis, electrospray ionization-time of flight-mass spectrometry (ESI-TOF-MS), electron spin resonance (ESR), and Raman spectroscopy. The experimental results demonstrate that a number of different oxidation states of manganese are involved in the decomposition reaction. Furthermore, the kinetics observed show oscillatory features that are characteristic of autocatalytic processes. Radical pathways were found to play a negligible role in the reaction. Based on the experimental observations, an overall reaction scheme for the decomposition process is proposed.
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August 8, 2005
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By means of bioassay-guided fractionation using mushroom tyrosinase, a geranylated stilbene, chlorophorin, was characterized as the principal tyrosinase inhibitor in the heartwood of Chlorophora excelsa (Moraceae). It inhibited the oxidation of L-tyrosine and DL-3,4-dihydroxyphenylalanine (DL-DOPA) due to mushroom tyrosinase and melanin biosynthesis on B16 melanoma cells. Chlorophorin, which is a slight yellowish compound, has previously been reported as an unstable compound in light. On the basis of this finding, a chlorophorin derivative [4-(3″,7″-dimethyloctyl)-2′,3,4′,5-tetrahydroxydihydrostilbene; hexahydrochlorophorin] which is colorless, obtained by the hydrogenation of chlorophorin with Pd/C, was also tested to develop a superior material for practical use. Hexahydrochlorophorin showed more potent inhibitory activity on tyrosinase and melanin biosynthesis, and lower cytotoxicity towards B16 melanoma cells than chlorophorin.
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August 8, 2005
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An oriented strand board (OSB) made of Scots pine ( Pinus sylvestris L.) was tested for volatile organic compound (VOC) emissions 24 h after the hot-pressing process over a period of 2 months. The predominant emissions from the OSB were monoterpenes and aldehydes. Terpene emissions decreased continuously, whereas aldehyde concentrations initially increased and subsequently decayed. Aldehydes are formed by the autoxidative splitting of unsaturated fatty acids contained in the wood. Due to the delayed release of aldehydes, a comparison of different emission test results is only possible if age and storage conditions are clearly specified. For a reduction in VOC emissions from wood-based materials, wood properties, manufacturing process, and storage conditions have to be considered.
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August 8, 2005
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The aim of this study was to propose an alternative non-deterministic and non-parametric technique for describing continuous variation in modulus of elasticity ( E ) within and between stems. The material studied consisted of hybrid Eucalyptus ( Eucalyptus urophylla × Eucalyptus grandis ) stems felled at the age of 59 months. Samples for measuring E were taken along a diameter slab at 1.30 m above ground. The results showed that the proposed reconstruction technique is consistent compared to results from other studies on Eucalyptus . E increases from pith to bark, following a polynomial distribution. Local and tree-averaged E increased with cambial age, following a sigmoidal profile that can be described with five characteristic parameters ( E at pith, E at inflection point, E after inflection point, cambial age when latency period ends, and cambial age at inflection point). The tree contributes little to the total variation. The most important changes in E value were found with increasing radial position, with this effect eight-fold more important than the tree effect.
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August 8, 2005
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The elastic properties of earlywood and latewood and their variability were measured in 388 specimens from six loblolly pine trees in a commercial plantation. Properties measured included longitudinal modulus of elasticity, shear modulus, specific gravity, microfibril angle and presence of compression wood. Novel testing procedures were developed to measure properties from specimens of 1 mm×1 mm×30 mm from earlywood or latewood. The elastic properties varied substantially circumferentially around a given ring and this variation was nearly as large as the variation across rings. The elastic properties varied by ring and height, but while the modulus of elasticity increased with height, the shear modulus decreased with height. A strong correlation was found between modulus of elasticity and shear modulus, but only at low heights and inner rings. Specific gravity and microfibril angle were the strongest predictors of elastic properties and explained 75% of the variation in modulus of elasticity for latewood. Despite being the best predictors in this study, these parameters accounted for less than half of the variability of earlywood modulus of elasticity, earlywood shear modulus and latewood shear modulus.
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August 8, 2005
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The mechanical treatment of wood in a refiner involves a complex combination of shear and compression forces. To obtain more knowledge on this process, the possibility of using an apparatus based on the Iosipescu shear test device to measure the behaviour of wood under a combined shear and compression load was tested. In this new apparatus, different combinations of shear and compression load were achieved by different rotations of the shear test device itself. Numerical simulations of the combined shear and compression test were carried out and compared with experimental data to verify the reliability of the modified device as applied to wood. It was concluded that the new apparatus is suitable for applying different combinations of shear and compression load in testing wood samples. However, finite element analysis showed that with the use of homogeneous material in the model, the level of strain reached would be 10-fold smaller. This fact is probably due to the honeycomb structure of the wood cells, which allows for different local deformation that could not be represented by the continuous material used in the model.
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August 8, 2005
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The main objective of this paper is to propose an alternative method for viscoelastic characterisation of wood-based panels. Our approach, based on inverse identification methods, allows simultaneous estimation of the whole bending/torsion stiffness matrix of orthotropic plates. Elastic or viscoelastic characterisations are carried out according to the same protocol. The first step consists of optimisation of the experimental set-up, i.e., determination of the best localisation and intensity of the applied stresses and of the best position for boundary conditions. This step is realised for each type of panel using generic algorithms to obtain sensitivities satisfying the test for each stiffness matrix component. An identification procedure is then performed using a finite element program. The measurement of the whole displacement field (500×500 mm 2 ) is made using an optical system. Validation of the elastic identification is carried out by comparison with the mechanical properties obtained from a vibrating test and a simulation tool. Non-conventional analysis of the viscoelastic behaviour of wood-based panels is illustrated for two particular plywood panels.
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August 8, 2005
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Measurements are reported of the mechanosorptive strain in Pinus radiata specimens stressed either in torsion or in bending. It is demonstrated that, to secure valid data, correction must be made for the moisture-induced distortion at zero load. A series of measurements can be made on a single specimen if two successive mechano-sorptive loading cycles are used and the sense of the stress is reversed for the second cycle. At the end of this procedure the specimen has reverted to its original dimensions. The mechanosorptive strain is shown to vary linearly with the applied stress; the ratio of the mechanosorptive strain to the initial elastic strain is therefore an appropriate way of quantifying the mechanosorptive effect. Analysis of torsion and bending data reveals that there is a strong correlation between the magnitude of the mechanosorptive strain and the shear stress component of the applied stress along the cellulose microfibril direction. It is suggested that the mechanosorptive effect arises from the effect of stress on the distribution of hydrogen bonds in hemicelluloses. A detailed model must await more information about the molecular structure of hemicelluloses in the cell walls.
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August 8, 2005
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Nitrous acid deaminative depolymerisation was used to prepare three chitosan oligomer (CO) mixtures from high-molecular weight chitosan. These mixtures of chitosan oligosaccharides were analysed by electrospray ionisation mass spectroscopy, potentiometric titration and gel permeation chromatography. A method based on potentiometric titration of the amino groups of the oligomers gave an average degree of polymerisation (DP) for the three preparations of 5 (CODP5), 9 (CODP9) and 14 (CODP14). Chitosan acetate and the chitosan oligomer mixtures were assayed against Leptographium procerum , Sphaeropsis sapinea and Trichoderma harzianum on nutrient media. Leptographium procerum and S. sapinea growth was prevented by chitosan acetate and chitosan oligomers at concentrations of 0.3–0.4% (w/v), whereas T. harzianum was able to overcome the fungistatic action of these compounds. The oligomer preparation CODP14 exhibited superior specific activity to both CODP5 and chitosan acetate, suggesting an optimum molecular weight for bioactivity. All oligomer preparations were more effective at pH 4 than at pH 6. This result, in combination with the inactivity of N -acetylated CODP14, indicated that amino group protonation was an important factor for fungistatic activity. The CODP14 preparation was reduced with sodium borohydride and fractionated by alkali precipitation and ion exchange chromatography. Bioassays of these fractions pointed towards DP and degree of deacetylation (DD) as key factors in chito-oligosaccharide bioactivity. Conversely, the terminal aldehyde groups generated by depolymerisation did not contribute to the activity observed.
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August 8, 2005
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This paper describes the use of quantitative real-time PCR for monitoring colonization of birch wood ( Betula pubescens ) by the white-rot fungus Trametes versicolor in an EN113 decay experiment. The wood samples were harvested after 4, 8, 12, 16 and 20 weeks of incubation. The mass loss was in the range of 4–40%. Chitin and ergosterol assays were conducted for comparison. Second-order polynomial fits of the mass loss of decayed wood versus chitin, ergosterol and DNA gave correlations (r 2 ) of 0.87, 0.61 and 0.84, respectively. Compared to the other two assays employed, real-time PCR data correlated best with the relative mass loss of decayed samples 4–8 weeks after inoculation, while the saturation and decline of DNA-based estimates for fungal colonization 16–20 weeks after inoculation indicated that the DNA assay is not suited for quantification purposes in the late stages of decay. The impact of conversion factors, extraction efficiency, inhibitory compounds and background levels in relation to the three detection assays used is discussed.
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September 1, 2005
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The adsorption of copper, [as Cu(II)], monoethanolamine (MEA) and didecyldimethyl ammonium chloride (DDAC) components of CuMEA and alkaline copper quaternary (ACQ) solutions impregnated into wood was followed by measuring the changes in solution concentrations in the wood over time. The rate and extent of copper and MEA adsorption were highly dependent on the solution strength and the conditioning temperature. Both copper and MEA were adsorbed by the wood structure with a rapid initial reaction, with higher relative amounts sorbed from lower concentration solutions. This was followed by a slower adsorption that still had not equilibrated after 7 weeks at 22°C. Generally, the adsorption pattern was similar for copper and MEA, suggesting that they were adsorbed as a copper MEA complex, with an MEA/copper molar ratio close to the theoretical maximum of 4. At a higher conditioning temperature of 50°C the reaction time was greatly reduced, with the adsorption after 1 week higher than after 7 weeks at 22°C, suggesting faster and more complete reaction at higher temperatures. DDAC was adsorbed more quickly and to a higher degree than Cu(II) for all treatment solutions and should be preferentially removed from such solutions, especially if empty-cell treatments are used. There appeared to be higher Cu adsorption from the higher concentration solutions of CuMEA than from corresponding ACQ solutions, likely due to DDAC competition with copper for the same reaction sites.
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September 1, 2005
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An approach to modeling leaching and leaching impacts of preservative components from treated wood is presented based on three simple laboratory determinations: the amount of preservative component available for leaching (Le), equilibrium dissociation of preservative into free water in wood (Di) and diffusion coefficients for component leaching in different wood directions ( D ). In this study, the following inorganic wood preservative systems were investigated: chromated copper arsenate (CCA), the copper component of copper azole (CA) and alkaline copper quaternary (ACQ), and boron in disodium octaborate tetrahydrate (DOT). Aggressive leaching of finely ground wood showed that amounts of preservative compounds available for leaching were highest for borates, followed by copper in copper amine systems and arsenic in CCA, copper in CCA and chromium in CCA. The equilibrium dissociation or solubility of components in free water in the wood was much higher for borates and copper amine, followed by copper and arsenic in CCA and chromium in CCA. Use of the applicable diffusion coefficient ( D ) and Di or Le values in a diffusion model allows the prediction of total amount leached and emission or flux rate at different times of exposure for products with different dimensions and geometries. The approach was tested and generally validated through application of the model to results of laboratory water spray leaching of full-size lumber samples. The approach explains the rapid leaching of boron compounds (large diffusion coefficient and high initial dissociated concentration) compared to other preservative components and predicts that ACQ will have higher initial leaching rates compared to CCA and CA, but the latter preservatives will continue to leach copper at a measurable rate for a much longer time. The practical implications and limitations of the approach are discussed.
