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July 5, 2005
Abstract
Molecular dynamics simulations were used to explore the distribution of linkages in coumaryl alcohol and coniferyl alcohol systems, including monomeric systems and monomers interacting with β-O4 dimers, respectively. Studying the interactions of two monolignols and the corresponding dimers sheds light on the preferred mechanism of reaction of the growing lignin polymer from the view of kinetic factors. The energy change upon association was quantified, and the distances between the centers of mass of different molecules, and the relative orientations between the phenol groups were calculated for all the systems. Using a cut-off threshold of 4 Å to indicate association leading to bond formation, it is concluded that the presence of the additional methoxy group on coniferyl alcohol assists in promoting interaction of the O4 group with the second moiety. Based on the computed data it is furthermore concluded that in aqueous solution, the most likely model of polymerization is that involving initial dimer formation, followed by dimer-dimer association.
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July 5, 2005
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Cellobiose dehydrogenase (CDH) is an extracellular enzyme produced by various wood-degrading fungi. It oxidizes cellobiose to cellobionolactone under reduction of molecular oxygen to hydrogen peroxide, and Fe 3+ to Fe 2+ . These activated agents can thereafter form highly reactive hydroxyl radicals, which depolymerize wood polymers. In this work, cellulose depolymerization by CDH was studied using a model compound, methyl β-D-glucopyranoside. The formation of glucose, arabinose, gluconic acid, erythrulose and formaldehyde were detected and a mechanism for the reaction is proposed. The biological importance of this enzyme-initiated reaction is discussed.
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July 5, 2005
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The reactivities of active oxygen species toward a non-phenolic lignin model compound, 1-(3,4-dimethoxyphenyl)-1,2-ethanediol (veratryl glycol, VG), and a carbo-hydrate model compound, methyl β-D-glucopyranoside (MGP), were examined and compared under practical oxygen bleaching conditions. In this study, active oxygen species were generated in situ by subjecting a phenolic compound, 2,4,6-trimethylphenol, to oxygen oxidation to faithfully simulate practical oxygen bleaching. The results indicated that the time-dependent reaction selectivity of active oxygen species between VG and MGP, k VG ( t )/ k MGP ( t ), in the early stage of the reaction is 2.1 and 0.3–0.7 at initial pH values of 11.8 and 13.1, respectively. By comparing this value with the of hydroxyl radical obtained by Ek et al. [Holzforschung 43 (1989) 391] we conclude that the active oxygen species in the early stage of the reaction are hydroxyl radicals. The reaction selectivity at higher pH was much lower, which is explained by the fact that an oxyl anion radical, the conjugate base of the hydroxyl radical, predominantly abstracts hydrogen from aliphatic substructures. Chain-type reactions could be mainly responsible for degradation of the model compounds after the middle stage of the reaction. We suggest that the operation of chain-type reactions is not greatly dependent on the pH of the medium, but on the structure of the substrate.
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July 5, 2005
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The proportion of erythro - and threo -forms of β-O-4-structures in lignin was elucidated by ozonation analysis of 21 wood species, and the relationship to the syringyl and guaiacyl composition was investigated. For all hardwood species, the erythro -form of β-O-4-structures predominated, although the extent varied widely, depending on wood species. In contrast, the proportion and amount of erythro - and threo -forms were very similar in all softwood species. The proportion of the erythro -form was greater in species with a higher methoxyl content in the lignin (correlation coefficient, R 2 =0.83). The S/V ratio (molar ratio of syringaldehyde and syringic acid to that of vanillin and vanillic acid) obtained by nitrobenzene oxidation was also strongly correlated with the proportion of the erythro -form (R 2 =0.99). Accordingly, the syringyl/guaiacyl ratio is closely related to the erythro / threo ratio. This stereochemical characteristic of β-O-4-structures is discussed in relation to the process of lignin formation.
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July 5, 2005
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July 5, 2005
Abstract
Spent chromated copper arsenate (CCA)-treated wood was liquefied in polyethylene glycol 400/glycerin (2:1w/w). Sulfuric acid (95–98%) and ferrous salts (FeSO 4 ·7H 2 O or FeCl 2 ·4H 2 O) were used as catalysts and additives, respectively. The resulting liquefied CCA-treated wood was diluted with aqueous solvents and was then mixed with complexion/precipitation agents, followed by precipitation or filtration to remove the toxic metal-bearing sediment. As a result, more than 90% of Cu, Cr or As was removed.
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July 5, 2005
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The optimum steaming conditions for extraction of condensed tannins from Acacia mearnsii bark were explored, after which characterization of proanthocyanidins from bark steamed under optimum conditions was carried out. The optimum conditions were as follows: steaming time, 30 min; steaming temperature, 140°C; and water volume, 75 ml. The total phenolics content obtained under these conditions amounted to 25.31%, which was much higher than the 21.70% obtained by conventional hot water extraction. Six proanthocyanidin dimers were isolated from the steamed bark. Analysis revealed them to be fisetinidol-(4β-8)-catechin, fisetinidol-(4α-8)-catechin, robinetinidol-(4β-8)-catechin, robinetinidol-(4α-8)-catechin, robinetinidol-(4β-8)-gallocatechin, and robinetinidol-(4α-8)-gallocatechin. Proanthocyanidin polymers were found to consist mainly of prorobinetinidin extender units, similar to those obtained from the same bark by conventional extraction with 70% acetone aqueous solution. However, nuclear magnetic resonance and gel permeation chromatography analyses suggested that during steaming the polymers undergo condensation reactions, as well as inversion of the configuration of interflavanoid bonds.
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July 5, 2005
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The chemical composition of the essential oil of Chamaecyparis formosensis wood has been examined. GC-MS data and retention indices for reference samples were used to identify 32 constituents. α-Eudesmol (18.06%), β-guaiene (8.0%), (–)-β-cadinene (7.89%), γ-costal (7.03%), α-muurolol (6.49%), 4α-hydroxy-4β-methyldihydrocostol (5.52%), σ-selinene (4.78%), santolina triene (4.60%), eremophilene (4.32%), humulene (4.11%), myrtenol (4.11%), and τ-cadinene (3.25%) were the most abundant components. Tests with the typical wood decay fungi, Laetiporus sulphureus and Trametes versicolor , proved the antifungal activity of the oil, as the growth of L. sulphureus and T. versicolor was inhibited at concentrations of 50 and 100 μg ml −1 , respectively. The following characteristic volatile compounds were isolated and purified from ethyl acetate fractions: epi -cubenol, chamaecynone, myrtenol, cis -myrtanol, 12-hydroxyisointermedenol and 4α-hydroxy-4β-methyldi-hydrocostol. Chamaecynone possessed the strongest antifungal activity, with an antifungal index of 88.2% and 67.3% for L. sulphureus and T. versicolor at a dose of 50 μg ml −1 , respectively.
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July 5, 2005
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Phenol-resorcinol-formaldehyde (PRF) and one-component polyurethane (PUR) resins were used to manufacture single lap joint samples corresponding to EN 302-1. 3D electronic speckle pattern interferometry (ESPI), which enables measurement of spatial displacement of less than 0.1 μm, was used during tensile shear experiments to observe full-field in-plane and out-of-plane deformation of the lap joint samples and to detect strain concentrations in the vicinity of glue lines. Finite element analysis was performed to validate ESPI measurements. In general, ESPI measurements showed that in a lap joint experiment a very small volume of material close to the ends of the overlapping area is highly strained. ESPI and finite element analysis pointed out that PUR glue lines are characterised by much higher shear deformations than PRF glue lines, especially at the ends of the overlapping area. However, due to the lower Young's modulus of PUR resin compared to PRF, higher shear strains but lower shear stress concentrations can be expected in PUR, which was confirmed by the FE model.
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July 5, 2005
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The effect of adhesive penetration into wood on the distribution of strain along a mechanically strained bond line was evaluated. With this goal, spruce wood specimens were bonded with phenol-resorcinol-formaldehyde (PRF) and one-component polyurethane resin (PUR). Penetration of the adhesives into cell cavities was observed in a zone extending over several 100 μm from the bond line. Electronic speckle pattern interferometry was used to record the elastic deformations caused by mechanical tests in transverse compression. By differentiating 2D displacement maps, the strain distribution was calculated. Both adhesives provided an increase in the stiffness of the adhesive-wood interface due to penetration into cell cavities. Compression strain was much lower in the bond line area than in the wood. Shear strain was also low in the bond line and increased gradually with increasing distance. No change was observed in wood unaffected by the adhesive. The effects were more pro-nounced for PRF resin than for PUR.
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July 5, 2005
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Recent biaxial experiments on spruce wood show that consideration of an elliptic failure surface according to Tsai and Wu and an elastic model for stress states within this envelope lead to an insufficient description of the mechanical behavior. As compression perpendicular to the grain occurs, a non-linear stress path results from a proportional biaxial strain path. Investigation of characteristic samples with respect to loading-unloading-reloading cycles for states of stress below failure reveals behavior similar to what is known as hardening type plasticity. The experimentally observed mechanical behavior is described by means of a two-surface plasticity model addressing both failure and non-linear stress response below failure as separate mechanisms. Prediction of failure is achieved by means of a second-order failure envelope according to Tsai and Wu. The non-linear stress response has to be covered by a novel orthotropic hardening type plasticity model. Since available experimental data covers only plane stress in the LR -plane, both orthotropic failure and yield surfaces, respectively, are restricted to this case.
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July 5, 2005
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In this study, sugar maple samples were impregnated with three impregnants by a vacuum and pressure process and in situ polymerized by a catalyst-thermal procedure. The effects of polymeric monomers and their combinations on monomer retention by volume (MR V ) and weight (MR W ) and polymer retention (PR) were analyzed and the wood was examined by scanning electronic microscopy (SEM). The three methacrylates chosen as impregnants were methyl methacrylate (MMA), hydroxyethylene methacrylate (HEMA) and ethylene glycol dimethacrylate (EGDMA). The formulation combinations were determined by a mixture design. MR V was similar, regardless of formulation combinations, which indicated that these methacrylates show similar permeability into sugar maple. However, MR W was different between formulation combinations due to differences in monomer density. MR V was inversely related to wood density. PR was related to the combination of impregnants and inversely related to wood density. The impregnants resided in the vessel and the lumen. The morphology of polymers in the wood was different for different treatments due to the distinct molecular structures formed from each polymer.
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July 5, 2005
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This work deals with the influence of poplar extractives and poplar alkaline degradation products on the hydration of cement. The wood chemical composition was characterized to determine the impact of soft alkaline conditions on wood fiber. Some of the constituents were hydrolyzed and converted into carboxylic acids, which were identified and quantified. Monitoring by electrical conductivity clearly showed that wood extractives are less effective than wood alkaline degradation products in inhibiting the hydration of cement.
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July 5, 2005
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This is a preliminary study that proposes an original prototype artificial neural network to be used in addition to the two classic sorption isotherm modeling methods, Hailwood-Horrobin (HH) and Guggenheim-Anderson-deBoer (GAB), in predicting the equilibrium moisture content in wood at three different temperatures (30, 45 and 60°C) for softwood (lodgepole pine) sapwood and heartwood specimens. Contrary to the HH and GAB equations, which use physical data for modeling, the predictive power of the artificial neural network is based on both physical and chemical data for the specific wood types. The results prove the potential efficient use of neural networks in predicting moisture content based not only on the ambient conditions, but also on taking into consideration the chemical composition of wood.
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May 1, 2005
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The hygroscopicity and hygro-mechanical properties of the adhesives, resorcinol-formaldehyde (RF) resin and aqueous vinyl polymer-isocyanate (API) resin have been examined. Adsorption isotherms for cured RF and API resins with various degrees of crosslinking showed that the hygroscopicity of both resins decreased as the curing reactions proceeded, although the mechanisms for these decreases differed. In RF resins cured with a large amount of hardener, a highly crosslinked structure is formed, so swelling is limited by the network. Thus, the hygroscopicity of cured RF resins decreases due to the restricted swelling, while the number of hydroxyl groups, another source of hygroscopicity, are not changed by the curing. On the other hand, swelling in API resins cured with a large amount of hardener is not completely inhibited because of long segments between the crosslinks. The hygroscopicity of cured API resins is lowered as the curing extent increased, since this reaction decreases the number of hydroxyl groups.
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May 1, 2005
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A generalisation of existing mechanical models is proposed to account for the relation between wood macroscopic properties and fibre microstructure and chemical composition. It is applied to understanding of the origin of anisotropic maturation strains measured at the outermost surface of the xylem. Various assumptions are considered for boundary conditions of the fibre during the progressive maturation process and are applied to experimental data from the literature. Assumptions that the fibre is fully restrained in displacement, or fully unrestrained or unrestrained in the transverse direction only are all incompatible with observations. Indeed, within the tree, the fibre is restrained in the longitudinal and tangential directions, but unrestrained in the radial direction towards the bark. Mixed boundary conditions must be introduced to correctly simulate both longitudinal and tangential maturation strains. In the context of an analytical axisymmetric model, this is estimated by considering a parameter of partial release of tangential stress during maturation. Consistence with data and with finite element computation in the case of a square fibre confirmed that, because of the unrestrained radial condition, a large part of the tangential maturation stress is released in situ .
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May 1, 2005
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Microtensile investigations were carried out on chemically and mechanically isolated fibres that had similar dimensions before isolation. The properties calculated for the fibres were nearly identical for the two isolation methods. However, cell wall cross-sections of chemically isolated fibres shrank much more transversely than those of the mechanically isolated fibres.
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May 1, 2005
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Colonisation and wood degradation by three brown-rot fungi, Coniophora puteana , Gloeophyllum trabeum and Poria placenta , were studied in wood of Norway spruce ( Picea abies ) subjected to three different treatments: hygro-thermal (TH) (160 and 180°C), mechanical densification and thermo-hygro-mechanical (THM) treatment including densification and post-treatment under saturated steam conditions at different temperatures (140, 160 and 180°C). The weight loss induced by all three fungi was lowest in THM-densified wood post-treated at 180°C. Highest weight losses were recorded for controls and TH-treated wood. Fungal colonisation varied in its intensity, depending on the treatment applied to the wood. Hyphal growth in controls and TH-treated wood was abundant, whereas in densified and THM-densified wood it was sparse and confined predominantly to the cell lumina of earlywood tracheids. Also, penetration of large-diameter hyphae and associated degradation in THM-densified wood was impeded by occlusion of the lumina, associated with irreversible compression (loss in shape memory). In contrast to C. puteana and P. placenta , which showed typical brown-rot behaviour, G. trabeum frequently showed hyphal tunnelling within the secondary walls of tracheids and xylem ray parenchyma of controls and thermally treated wood. Such growth was never observed in THM-densified wood post-treated at 180°C.
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May 1, 2005
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This is the final report on a study that examined the occurrence of three types of microorganisms (fungi, bacteria, and yeasts) on dead-stacked green yellow-poplar lumber in spring and summer of 2000. This paper reports on the abundance, identities, and diversity of yeasts isolated during the first 60 days of storage of the lumber immediately after sawing in each season. Yeasts made up 16% of the total microbial isolates (log n cfu g −1 ) in the entire study. The predominant yeast isolate was Trichosporon cutaneum , which accounted for 42% of all the yeasts identified. A great variety of yeast species belonging to the genus Candida were present and included C. steatolytica , C. sphaerica , C. humicola , C. incommunis , C. montana , and C. kefyr .
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May 1, 2005
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Ground-contact stakes, made from defect-free southern yellow pine sapwood, were treated with water-borne copper(II) [ammoniacal copper carbonate, ACC, Cu(II)] alone, oil-borne oxine copper (Cu-8) alone, or a dual treatment of ACC followed by drying and then Cu-8. The treated stakes were installed at two locations in Mississippi (Dorman Lake and Saucier) in high- or severe-deterioration hazard zones and inspected after 69 months of exposure. Stakes treated with Cu(II) alone at the highest retention of 5.1 kg m −3 [copper retention is based on the copper oxide (CuO) weight, as is standard in the US] performed moderately well at the Saucier test site, with decay and termite ratings of 8.0 out of 10.0, but unsatisfactory at the Dorman Lake test plot, with decay and termite ratings both below 7.0. Samples treated with Cu-8 alone at the highest retention of 1.92 kg m −3 had poor termite protection, with ratings below 7 at both sites, and only fair decay ratings of 7.0 (Dorman Lake) and 7.6 (Saucier). In contrast, all stakes treated with Cu(II)/Cu-8 combinations, with at least 2.4 kg m −3 Cu(II) and 0.2 kg m −3 Cu-8, performed satisfactorily, with average decay and termite ratings all above 8.0 at both locations. The addition of Cu(II) to Cu-8 likely causes the di-ligand form [bis(8-hydroxyquinolinolate)Cu(II)] to equilibrate principally to the mono form. Thus, the combination of Cu(II) and Cu-8 appears to form a new compound with greater efficacy than either of the two starting “reagents” and, consequently, this mixture is not literally synergistic. Possible advantages of mono Cu-8 include: (1) the mono form may be easier to formulate in a water- or solvent-borne system than the commercial bis-Cu-8 biocide; (2) the preservative would have a relatively low metal content, which may make future disposal of treated wood easier; (3) this system would likely have much fewer metal corrosion problems than preservative systems formulated with uncomplexed copper(II); and (4) the two copper coordination sites that are not complexed with the ligand could bind to the carboxylic or phenolic groups in wood to make the mono form relatively leach-resistant.
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May 1, 2005
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MALDI-TOF MS differentiated mycelia within pairs each of the closely related indoor wood decay fungi Serpula lacrymans , S. himantioides , Coniophoraputena , C. marmorata , and Antrodia vaillantii , A. sinuosa . The method is thus suitable to identify unknown samples by spectrum comparison.
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