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June 1, 2005
Abstract
Hydrolysis of bordered and pinoid pits may be a key event during colonization of wood by decay fungi. Although pits are numerous, studies of pectin-hydrolyzing enzymes in wood decay fungi are scarce, probably because of the relatively low content (less than 4 %) of pectin in wood and because of the primary focus on understanding the degradation of lignified components. Endopolygalacturonase (endo- PG) activity was estimated by cup-plate assay and viscosity reduction of pectin from liquid cultures of fifteen brown-rot and eight white-rot basidiomycetous fungi using sodium polypectate as the carbon source. Oxalic acid was estimated in liquid culture and related to mycelial weight of each fungus. Changes in longitudinal gas permeability of southern pine cores exposed to selected decay fungi in liquid culture were measured to determine the extent of hydrolysis of bordered pits. Twelve of fifteen brown-rot and six of eight white-rot fungi tested were positive for at least one of the polygalacturonase test methods. Accumulation of oxalic acid was detected in thirteen of fifteen brown-rot isolates and none of the white-rot fungi tested. Gas permeability of pine cores increased approximately fourfold among brown-rot fungi tested and eighteenfold among white-rot fungi tested. Scanning electron microscopy revealed bordered pit membrane hydrolysis in cores colonized by white-rot fungi, but only torus damage, weakening and tearing of the pit membranes, was observed in cores exposed to brown-rot fungi. We conclude that both brown- and white-rot decay fungi have the enzymatic capacity to hydrolyze pectin, damage bordered pit membranes, and increase wood permeability during colonization and incipient decay.
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June 1, 2005
Abstract
The attraction of steamed Japanese larch ( Larix leptolepis (Sieb. et Zucc.) Gord.) heartwood to the subterranean termite, Coptotermes formosanus Shiraki was investigated. Hot-water extracts of the steamed and the non-steamed larch woods were sequentially extracted with n -hexane, diethyl ether, and ethyl acetate. Furthermore, the residual water-soluble fraction of the steamed wood was fractionated by column chromatography using an Amberlite XAD-2 resin. Feeding-preference and feeding-deterrence of the termite were assessed in the two-choice feeding tests using paper discs permeated with each fraction. The diethyl ether extracts of the non-steamed larch wood showed the feeding-deterrence activity. Taxifolin, the main component of these extracts, was found to be the major feeding-deterrence constituent. In the case of the steamed larch wood, taxifolin was not detected in any fractions, and the residual water-soluble fraction showed the feeding-preference activity. Furthermore, it was found that the feeding-preference constituents were contained in the coloring substances adsorbed by the Amberlite XAD-2 resin. From these results, the degradation of taxifolin and the formation of coloring substances during the steam treatment were to be considered as important factors of the attraction of steamed larch wood to the termite.
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June 1, 2005
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The objective of the study was to investigate whether soluble sugars and nitrogenous compounds in wood have an impact on susceptibility of wood to decay in ground contact, which is important in the field of test methodology and standardization. Kiln drying of Scots pine planks caused a distinct gradient of low-molecular weight (LMW) sugars and nitrogenous compounds in the 0–2 mm zone at the surface of the timber, whereas the deeper zones had constant and low contents of soluble substances. Strips, containing different content of soluble nutrients, were cut and exposed in two types of soil; the former one being rich in soft rot fungi, the latter one being rich in soft rot fungi and bacteria. The strips rich in nutrients showed an average of 16 % of mass loss whereas samples poorer in nutrients were less affected (8–9 %) after 120 days of exposure in the soil rich in soft rot fungi. A pure culture test with the soft rot fungus Phialophora mutabilis confirmed the above-mentioned observation. The result is in favour of taking samples with approximately equal content of soluble nutrients to decrease the variability of test results, e.g., mass losses. The garden compost, rich in both soft rot fungi and bacteria, caused severe mass loss (40–48 %) of the strips after 120 days of exposure. No difference in the mass losses of the samples was measured. The choice of test soil as well as the nutrient status of the samples can lead to completely different results and, consequently, conclusions.
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June 1, 2005
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In this work, carboxylic acids of the Moroccan Pinus pinaster bark were studied and analysed by High Performance Liquid Chromatography (HPLC), Thin Layer Chromatography (TLC) and Gas Chromatography coupled with Mass Spectrometry (GC-MS). Several acids, such as gallic, p-hydroxyphenylacetic, 3,4-dihydroxyphenylacetic, salicylic, shikimic, protocatechuic, terephtalic, ferulic, p-coumaric, vanillic, caffeic and isovanillic acids, were detected by direct injection of standard products and by studying the mass spectrum of their trimethylsilyl derivatives.
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June 1, 2005
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Data suggest that the dimerization of coniferyl alcohol is not under thermodynamic control. In this study, molecular dynamics calculations were used to estimate the effect of the solvent environment. In water, the coniferyl alcohol radicals were forced to associate by the formation of a solvent cage. In glycerol, the solvent cage effect appeared to be absent. These results suggest that in water, the product distribution of the dimers will be modified by interactions with the solvent. The computed results are consistent with experimental observations of coniferyl alcohol reactions in various solvents.
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June 1, 2005
Abstract
Acetic acid lignins from rice straw (RLs), birch (BL) and fir (FL) were chemically characterized by means of elementary analysis, functional groups analysis, alkaline nitrobenzene and permanganate oxidation, Mannich reactivity and other techniques. The results showed that RLs had higher contents of residual polysaccharide and protein, and remarkably fewer acetyl groups than BL and FL. Results of nitrobenzene and permanganate oxidation indicated that RLs were remarkably more condensed than the native lignin in rice straw. In addition, the results of Mannich reactivity showed that RLs were more reactive toward modification than BL and FL, and might be a good raw material for lignin derivatives, such as lignin adhesives and chelating resins.
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June 1, 2005
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The rapid FTIR (Fourier transform infrared) spectroscopy technique was used to indirectly measure the lignin content of Sitka spruce wood samples. A model was constructed to relate FTIR data to lignin content measured in wood by chemical analysis (i.e. the modified acetyl bromide method), through the application of the principal component regression (PCR) approach to a set of calibration observations. The acetyl bromide method provided lignin determinations ranging from 24% to 34% with a measurement error of 0.6%. A residual standard deviation of 0.8% and an average prediction error of 0.9% were calculated for lignin content when employing the selected PCR model (based on a normalized infrared data set, obtained using the band at 1374 cm −1 as a reference) to indirectly measure this wood property. Furthermore, a large portion of the variability in lignin content was explained by the two principal components retained in the selected calibration model, as indicated by the magnitude (i.e. 0.93) of the coefficient of multiple determination. The model was subsequently employed to predict the lignin content of wood samples collected in a clonal experiment. Two multivariate diagnostic measures were applied to assess the quality of the individual predictions, and the results indicated that the spectral information contained in the new sample vectors was suitable for use with the selected calibration model.
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June 1, 2005
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The permanganate oxidation method was used to analyze residual lignins in Norway spruce ( Picea abies ) organosolv pulps. The pulps were produced by ethanol water solvolysis catalyzed by 0.005M or 0.01M H 2 SO 4 at 175 °C. Condensation reactions of residual lignin occurred at a significant rate when the ethanol volume fraction was 0% but not when it was ≥ 51 %. There was selective removal of uncondensed guaiacyl units when mixtures of 51 %, 76%, and 91% ethanol were used. The condensed units in the native lignin were less reactive and accumulated in the fibers. They constituted > 60 % of the C 9 units by the time 80 % delignification was achieved. A limited amount of results are presented for a kraft pulp with hopes of enhancing the credibility of permanganate oxidation as an analytical tool for residual lignins.
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June 1, 2005
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The conversion of different types of lignin to monophenolic compounds has been studied between 500 and 650 K, under typical coal liquefaction conditions using 9,10-dihydroanthracene (AnH 2 ) and 7 H -benz[ de ]anthracene (BzH) as the hydrogen-donor solvents. The yield of phenolic compounds was found to increase with the capacity of the hydrogen donor. The application of a polar cosolvent appeared to be beneficial as well. The differences in product distribution could be related to the origin of lignin. The maximum yield amounted to 11 % after 4 h at 625 K using milled wood lignin in AnH 2 . It has been found that lignin itself is a hydrogen-donating substance and capable of cleaving aromatic ketones such as α-phenoxyacetophenone.
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June 1, 2005
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Four softwood and three hardwood species were liquefied using polyethylene glycol (PEG) or glycerol-containing PEG solvent systems as liquefaction reagents under defined reaction conditions: wood / liquefaction reagent / sulfuric acid = 3.00/9.00/0.27 gram, at 150 °C. The percentage residues and hydroxyl numbers were determined as an estimate of polyol value of the solution. The PEG system yielded 10–30% residual materials even under the best reaction conditions since low -OH group content resulted to re-condensation of liquefied wood (LW). The hydroxyl numbers linearly decreased from 210 to 100 mg KOH/g on extended (150 min) reaction time. On the other hand, addition of 10% glycerol to the PEG system resulted in small amount of unliquefied residues (~ 3%) and a stable hydroxyl number, regardless of the wood species tested. In case of 60 min reaction time, the mean residue value was 5.8% and a corresponding mean hydroxyl number of 216.1 mg KOH/g was obtained. This system is deemed suitable for liquefaction of a wide variety of wood species.
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June 1, 2005
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Chlorine dioxide delignified pulp was subjected to various oxidative alkaline extraction stages (EAr, E, EO, EP, and EPO) from which the residual and effluent lignins were isolated and characterized by 1 H and 13 C NMR. Results of the NMR analyses indicate an increase in unconjugated carboxyl content of the lignins with the alkali treatment; a decrease in phenolic and formyl groups with oxidant reinforcement, especially oxygen; and an enrichment in aromatic methoxyl groups with increasing amount of oxidant reinforcement. The alkaline extracted pulps were further treated to a second chlorine dioxide stage from which the residual lignins were extracted and analyzed by 1 H NMR. Significant structural differences were noted between the various oxidative E stage and D 1 stage lignins.
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June 1, 2005
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A novel plasma-enhanced coating for wood substrates has been developed which diminishes the degradation of wood under simulated harsh environmental conditions. Reflective (zinc oxide) and electromagnetic radiation (EMR)-absorbent (benzotriazole, 2-hydroxybenzophenone, phtalocyanine, and graphite) substances were incorporated into a liquid phase, high-molecular-weight polydimethylsiloxane and deposited as thin layers on wood surfaces. The macromolecular films, containing the dispersed materials, were then converted into a three-dimensional solid state network by exposure to a 30 kHz-oxygen-RF-plasma. The discharge induced chemistry and altered surface topographies in the surface layers were monitored by survey and high resolution Electron Spectroscopy for Chemical Analysis, Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy, and Scanning Electron Microscopy. The surface characteristics and the resistance to weathering of the plasma treated substrates were evaluated and compared to the properties of un-modified samples.
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June 1, 2005
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Volatile organic compounds (VOCs), principally terpenes, released during wood drying face present or potential regulation. Two approaches are reported to control VOC release: heating green wood, or irradiating it with microwave energy, both in a low-headspace environment where evaporation is minimized. Low-headspace heating of green flakes (for OSB manufacture) releases VOCs but proportionately much less water. Hence, it is feasible to extract and collect the VOCs from green wood prior to drying, and to then dry it with lowered emissions. Irradiating flakes with microwave leads to contrasting behavior. Water is released with very little VOC loss if the flakes are microwaved in an open container. Microwaving under low-headspace conditions removes the VOCs, but retains the water in the wood. The water trapped in the wood because of the low-headspace restriction drives the VOCs out of the hydrophobic regions ( e.g. , resin canals) where they are principally located, into hydrophilic zones. Movement out of the hydrophilic environment and out of the wood is then quite rapid. Hence, either VOC or water release can be targeted by adjusting the headspace during microwaving. Most of the VOCs lost during drying originate from the surface, and low-headspace microwaving releases this surficial material. Hydrogen isotope exchange work shows that microwaving increases water access to the exchangeable protons in dry, or partially dry, wood tissue. The terpenes are carried out with the small amount of steam generated. Similar results are obtained with low-headspace radiofrequency (RF) irradiation of lumber; RF treatment does not induce a significant change in strength.
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June 1, 2005
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Environmental Scanning Electron Microscopy, ESEM, was used to investigate microautoradiographs of Scots pine ( Pinus silvestris L.) sapwood painted with a priming oil containing 14 C-labelled alkyd paint binders. Microautoradiography is a photographic method which reveals the localization of compounds labelled with a radioactive isotope in the investigated material. The photographically developed silver grains in the microautoradiograph indicate where the labelled compounds are situated. Microautoradiographs were investigated with ESEM in their natural state, without conventional preparation techniques which are time-consuming and may cause unwanted artefacts. It is demonstrated that the wood structure is clearly visible in the mainly transparent photographic film of the microautoradiographs. Images produced by the backscatter emission detector were of high quality, silver grains and wood structure are visible at the same time and the images are almost without artefacts due to charge built-up, which it is not possible to achieve using a conventional SEM. The investigation of penetration into wood with microautoradiography can thus be conveniently evaluated by ESEM.
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June 1, 2005
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The effect on glue joint strength of removing the layer of cells on end-grain surfaces of wood damaged by machining—the mechanical weak boundary layer (MWBL)—is presented. The wood surfaces have been laser ablated using different types of lasers of different wavelengths. The goal has been to determine whether or not the strength of end-grain glue joints is influenced by the MWBL and to show how the laser wavelength affects the glue joint strength. All tests were carried out with a PVAc-glue with hardener, and two different glue pressures were used. The joints were tested by bending notched and fatigued specimens. The statistical evaluation of the results shows that one laser gave a significantly higher glue joint strength than the others. One main conclusion is that the glue joint strength could have been improved with a stronger glue. An ESEM-analysis showed that fracture occurred primarily in the glueline and not in the boundary layer.
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June 1, 2005
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Dielectric properties from 1 to 18 GHz of rubber wood are modeled using generalized mixture equations and also with equations proposed by Weiner, Kraszewski, Looyenga and Landou, Lichtenecker. Dielectric properties were measured with an open-ended coaxial line-sensor in three structural directions longitudinal, radial and tangential and at different moisture contents. The dielectric constants were predicted well by the Weiner model for all structural grain directions and it was found that the degree of binding decreases with increasing frequency. However, the Weiner model cannot be used for predicting the dielectric loss factor at frequencies below 3 GHz. This may be due to the high conductive loss in this frequency region. The lower value of the exponents in generalized mixture equation was found suitable for fitting the experimental data as well as the Kraszewski equation. Values predicted by Lichtenecker equations are in well agreement with the experimental data at higher microwave frequencies. The prediction of dielectric loss factor using Kraszewski, Looyenga equations were not possible at frequencies below 3 GHz since it is dominated by conductive loss. Above 3 GHz, it was well predicted by Kraszewski and Looyenga equations.
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June 1, 2005
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For the purpose of understanding the swelling phenomenon of wood in liquids, the contributions of enthalpic and entropic terms to the standard free energy change of adsorption have been determined by measuring the temperature dependence of adsorption isotherms. The values of standard enthalpy change of adsorption are smaller for alcohols having both proton-accepting and -donating properties than for acetone having only a proton-accepting property. The results are discussed in terms of the proton-accepting power and the cohesive energy of the respective adsorbate liquids. Methanol showed a larger isosteric heat of adsorption to dried wood than to pre-swollen wood, and the amounts of methanol and acetone adsorbed on dried wood exceeded those on swollen wood within the low activity range. These results indicate the presence of more exothermic sites in dried wood than in pre-swollen wood, and of pre-existing spaces and/or parts loosely hydrogen-bonded between wood constituents in the cell walls of dried wood.
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