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December 5, 2007
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December 5, 2007
Abstract
In biopulping, efficient wood colonization by a selected white-rot fungus depends on previous wood chip decontamination to avoid the growth of primary molds. Although simple to perform in the laboratory, in large-scale biopulping trials, complete wood decontamination is difficult to achieve. Furthermore, the use of fungal growth promoters such as corn steep liquor enhances the risk of culture contamination. This paper evaluates the ability of the biopulping fungus Ceriporiopsis subvermispora to compete with indigenous fungi in cultures of fresh or poorly decontaminated Eucalyptus grandis wood chips. While cultures containing autoclaved wood chips were completely free of contaminants, primary molds grew rapidly when non-autoclaved wood chips were used, resulting in heavily contaminated cultures, regardless of the C. subvermispora inoculum/wood ratio evaluated (5, 50 and 3000 mg mycelium kg −1 wood). Studies on benomyl-amended medium suggested that the fungi involved competed by consumption of the easily available nutrient sources, with C. subvermispora less successful than the contaminant fungi. The use of acid-washed wood chips decreased the level of such contaminant fungi, but production of manganese peroxidase and xylanases was also decreased under these conditions. Nevertheless, chemithermomechanical pulping of acid-washed samples biotreated under non-aseptic conditions gave similar fibrillation improvements compared to samples subjected to the standard biodegradation process using autoclaved wood chips.
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December 5, 2007
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The polysaccharide xyloglucan as a wet-end additive improves paper properties. In the present study, paper strength improvement was analysed for dry handsheets made from chemical, mechanical and recycled pulps coated with xyloglucan in a spray application. Results are compared with sheets made from the same pulps treated with xyloglucan in the wet-end. Kraft pulp handsheets of bleached hardwood and softwood showed significant improvements of tensile, tear and Z-strength by xyloglucan spray treatment versus wet-end application, whereas handsheets of de-inked and thermomechanical pulp were improved only slightly. In both wet-end and spray applications, the effect of xyloglucan addition was intimately related to the presence of non-cellulosic components on the fibre surface. Further strength improvements were obtained for chemical pulps by addition of borax to the spray solution, which were likely to be due to the formation of borate-mediated xyloglucan cross-links. Spray coating of xyloglucan, with or without borax, thus represents a potential new application of this polysaccharide to increase paper dry strength.
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December 5, 2007
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A new method for the isolation of lignin in high yield from wood and pretreated wood is presented, avoiding the liquid-solid extraction step of the classical milled wood lignin (MWL) isolation. Dissolved wood lignin (DWL) was obtained by total dissolution of ball milled wood in dimethylsulfoxide and N -methylimidazole (DMSO/NMI) followed by precipitation in dioxane/water in the course of which lignin and carbohydrate fractions were separated. The lignin fraction was purified. High lignin yields and the low number of separation steps belong to the advantages of the described method. DWL lignin was isolated from beech wood ( Fagus sylvatica L.) and the sample was compared to MWL obtained by the classical Björkman method. Elemental analyses, methoxyl group content, potassium permanganate oxidation, infrared spectroscopy, and 1D and 2D nuclear magnetic resonance spectroscopy indicated that both lignin preparations are quite similar. However, MWL contained significantly more phenolic hydroxyl groups than DWL. The results indicated that MWL contains higher amounts of smaller fractions with broken β-O-4 linkages than DWL.
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December 5, 2007
Abstract
Despite the growing importance of Eucalyptus wood as raw material for pulp and paper, there is a lack of knowledge on the chemistry of their macromolecular components. The present paper addresses this issue by applying the recently developed protocol for isolating enzymatic mild acidolysis lignins (EMAL) from Eucalyptus grandis , Eucalyptus globulus and the softwood species Douglas fir and white fir, which were used for comparative purposes. The structures of EMALs were investigated by quantitative 31 P NMR, DFRC/ 31 P NMR (derivatization followed by reductive cleavage followed by quantitative 31 P NMR) and size exclusion chromatography (SEC). Overall, the yields of EMALs isolated from Eucalyptus were higher than those from the softwoods examined. Lignin from E. globulus was found to contain higher contents of arylglycerol- β -aryl ether structures, free phenolic hydroxyl groups and syringyl-type units than lignin from E. grandis . New insights provided by the DFRC/ 31 P NMR revealed that up to 62.2% of arylglycerol- β -aryl ether structures in E. globulus are uncondensed, while in E. grandis the amount of such uncondensed structures was found to be lower than 48%. SEC analyses showed that lignins from E. grandis and softwoods associate in greater extension than lignin from E. globulus .
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December 5, 2007
Abstract
There is a need for efficient separation processes that provide clean fractions of individual wood polymers. The purpose of this study was to remove lignin from a xylan rich fraction from birch by solid-liquid extraction followed by a liquid-liquid extraction. By this means, it was possible to diminish the lignin concentration (12%) of mildly extracted xylans from birch to a total lignin concentration of 3%, as determined as a sum of Klason lignin and acid soluble lignin. The molecular masses of the fraction were determined by size exclusion chromatography (SEC). The two xylan rich fractions obtained by the removal of lignin have molecular masses ( M W ) of 15 300 and 27 900 Da in comparison to 11 900 Da for the lignin rich starting material. NMR and IR analysis revealed that the lignin removed is mostly unbound to the polysaccharides. The lignin was water soluble in the presence of xylan (as part of the xylan rich fraction), but not in isolated form in water alone. The remaining lignin in the xylan fractions has obviously a closer interaction with the xylan, and thereby its separation by liquid-liquid extraction is more difficult. It is also observed with NMR that the extractable lignin is built up mainly of syringyl units, chiefly bonded by β-O-4 linkages.
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December 5, 2007
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Various lignin model compounds were oxidized with polyoxometalate (POM), K 5 [SiVW 11 O 40 ]·12 H 2 O, in sodium acetate buffer ( I =0.2 M, pH 5.0) and the reaction kinetics were investigated. The reactions were found to have second order reaction rates, first order with regards to both lignin model compound and POM. A dramatic increase in reactivity was observed upon addition of methoxyl groups in ortho -positions to the phenolic hydroxyl group. Syringyl units reacted faster than guaiacyl units. Reaction rates of para -substituted guaiacyl and syringyl model compounds showed a strong dependency on the nature of the substituents. The reaction rate of a 5-5′ dimer lignin model compound was extremely fast. The addition of the ortho -phenol substituent not only increased the electron density of the aromatic ring, but also helped stabilize the intermediate phenoxy radical through resonance stabilization and delocalization.
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December 5, 2007
Abstract
Pyrolytic cleavage mechanisms of lignin-ether linkages were studied with some dimers and trimers which have various p -substituted C α -phenoxy groups (-H, -OCH 3 , -Cl or -COCH 3 ). Pyrolysis of these model compounds provides phenols and isoeugenol type products. To determine whether the reactions mechanisms are heterolytic or homolytic, the reactivities were compared based on Hammett's substituent constant (σ p ) and the ΔBDE parameter, namely the bond dissociation energy (BDE) reduction. The α-ether-linkages in phenolic forms are cleaved in a heterolytic mechanism, while in non-phenolic forms the α-ether linkages are cleaved homolytically. Cleavage of these α-ether linkages is the rate-determining step for the scission of the C β -O bond in trimers. The β-ether-linkages in the non-phenolic trimers are cleaved through the β-scission type reaction from the benzyl radical intermediates. On the other hand, quinone methide formation through heterolytic cleavage of the α-ether linkages is the key step for following homolysis of the C β -O bonds in the phenolic trimers. Electron attracting character of the quinone methide structure reduces the BDE of the C β -O bond.
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December 5, 2007
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A rather extensive degradation of cellulose and hemicelluloses was found in waterlogged oak wood samples from the ancient warship Vasa by size exclusion chromatography with the solvent system lithium chloride/N,N-dimethylacetamide (LiCl/DMAc). The degradation has mainly occurred after salvage of the wreck, probably as a consequence of keeping iron contaminated wood in contact with air. The most likely explanation is Fenton type of reactions degrading the wood polymers and oxidising reduced sulphur forms to sulphuric acid. An increased degradation rate of the Vasa wood can be anticipated in the future if the sulphuric acid cannot be neutralised and the oxidative reactions cannot be quenched.
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December 5, 2007
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Mass spectrometric analysis of aqueous wood extracts from the Swedish warship Vasa reveals a serious chemical condition in the depth of the wood. The surface is less affected. Polyethylene glycol, used as conservation agent, is affected and partly degraded, and low-molecular fragments from hemicellulose are found at sites with high iron content and low pH. These findings imply a catalytic oxidative process and acidic hydrolysis in the wood, which contributes to a new picture of the challenge of long-term preservation of the Vasa .
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December 5, 2007
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Utilization of rapidly growing trees, such as eucalypts, for high-yield mechanical pulps is limited by low brightness owing to high contents of alkali and neutral extractives. Wood supply problems have developed in many areas of the world and new sources of high-yield pulp are needed. Ten Eucalyptus globulus trees were selected from two plantation sites to evaluate suitability as raw material for high-quality and high-yield pulp. Chemithermomechanical pulp (CTMP) was prepared from tree chips pretreated with sodium sulfite prior to refining. Characteristics of the CTMP were correlated with chemical and physical properties of the wood. There was a linear relationship between the content of alcohol-benzene extractives in wood and CTMP brightness. Klason lignin content in wood was inversely correlated with pulp sheet density, which is an important characteristic affecting the physical properties of pulp. The content of alkali extractives were inversely correlated with pulp yields. Color reversion was tested by exposing CTMP sheets to heat and light. Heat-induced yellowing of CTMP was of a low level and satisfied requirements for printing paper. The rate of yellowing was inversely associated with extractives and can be reduced by antioxidants.
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December 5, 2007
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Axial compressive stresses can cause distortion of the cellulose fibril alignment in the wood cell wall. These deformations are thought to occur in the living tree and/or to develop during wood processing and seem to adversely affect the mechanical properties of pulp and paper and other fibre-based products. To characterise the influence of dislocations on the mechanical properties of the unmodified cell wall, dislocations were artificially created by applying high compression loads to wood blocks parallel to the fibre axis. Mechanically isolated fibres containing different levels of dislocations were then subjected to tensile tests. Comparison between micromechanical properties of reference fibres and fibres that were artificially loaded in compression revealed the importance of dislocations for the mechanics of both earlywood and latewood. However, the tensile strength (decrease ∼19% for earlywood and ∼26% for latewood) was less affected than expected from structural observations of the pre-compressed zones.
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December 5, 2007
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Mode I and Mode II initiation fracture toughness was examined by DCB (double cantilever beam) and 3ENF (three-point bend end notched flexure) tests on specimens of compressed Sitka spruce. The compressed wood was fabricated by varying the compression ratio, and the effectiveness of the compression treatment was examined in view of improving the fracture mechanics properties. In both cases, the fracture toughness did not show a significant increase after the compression treatment. Thus, it would be necessary to develop a new compression treatment method to improve the fracture mechanics properties.
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December 5, 2007
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Experimental results are presented with single nail joints of gonfolo rose which were loaded at different grain angles and compared to results obtained by Eurocode V. A wide range of embedding strength tests was conducted. The embedding behaviour across the grain was also investigated with a specific test apparatus. The results were analysed and modelled in terms of strength. Initial loading and unloading stiffness of the timber have been taken into account. The embedment strength of the nails varied according to the angle between the direction of loading and that to the grain. This work is part of a larger research project to establish a computer program for the prediction of stiffness and limit strengths of all timber-to-timber and timber-to-steel joints.
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December 5, 2007
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Cross sections of wood adhesive bonds were studied by scanning thermal microscopy (SThM) with the aim of scrutinizing the distribution of adhesive in the bond line region. The distribution of thermal conductivity, as well as temperature in the bond line area, was measured on the surface by means of a nanofabricated thermal probe offering high spatial and thermal resolution. Both the thermal conductivity and the surface temperature measurements were found suitable to differentiate between materials in the bond region, i.e., adhesive, cell walls and embedding epoxy. Of the two SThM modes available, the surface temperature mode provided images with superior optical contrast. The results clearly demonstrate that the polyurethane adhesive did not cause changes of thermal properties in wood cell walls with adhesive contact. By contrast, cell walls adjacent to a phenol-resorcinol-formaldehyde adhesive showed distinctly changed thermal properties, which is attributed to the presence of adhesive in the wood cell wall.
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December 5, 2007
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The marine borer Limnoria ingests essential wood components including the extractives the wood contains. Some extractives may confer borer resistance on certain timbers. Feeding by Limnoria correlates with the rate of production of faecal pellets. The faecal pellet production rate and mortality on over 40 test timbers and non-resistant Pinus sylvestris sapwood was measured over 15 days. By placing animals in leachate from wood and with wood in flowing seawater, the effects of leaching-resistant and water-soluble compounds were measured. Some previously untested timbers affected Limnoria as strongly as timbers reputed for durability in marine construction. Wood of Minquartia guianensis , Nectandra rubra and Bruguiera gymnorhiza caused high mortality, and pellet production on them was less than 10% of production on P. sylvestris . Suppressed feeding rates, but with no heavy mortality, were observed on known durable species such as Chlorocardium rodiei , Dicorynia guianensis, Lophira alata and Nauclea trillesii , but also on Cynometra ananta , Distemonanthus benthamianus , Enterolobium schomburgkii , Goupia glabra , Hymenaea courabil , Mammea africana , Shorea sp. and Sacoglottis guianensis . Leachate from B. gymnorhiza , G. glabra , H. coubaril , N. rubra and Shorea sp. caused high mortality. These short-term bioassays thus detected clear differences between wood species in their resistance to Limnoria that matched findings from long-term marine trials, while indicating new species worthy of detailed testing.
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December 5, 2007
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An amino-silicone (AS; amino-polydimethylsiloxane) micro-emulsion was tested for its suitability to preserve wood against basidiomycetes in a mini-block experiment and in a test according to the European standard (1996) EN 113. Decay resistance was assessed against the white rot fungi Trametes versicolor , Ceriporiopsis subvermispora , and Hypoxylon fragiforme , as well as the brown rot fungi Coniophora puteana , Antrodia vaillantii , Gloeophyllum trabeum and Serpula lacrymans . Pine sapwood and beech wood were treated with AS emulsions at solute concentration levels of 2%, 5% and 15%. The mini-blocks treated with 15% concentrations of AS resisted decay by T. versicolor and C. puteana over a long time (12 weeks), while samples treated with low and moderate concentrations underwent considerable mass losses. Accordingly, microscopic studies revealed a high degree of colonisation by the white rot fungus and loss of cell wall integrity (brown rot) in samples treated with 2% AS. At high AS content (15%), no or only initial stages of decay could be observed. In the European standard (1996) test EN 113, the mass loss in all fungal cultures except for the white rot ascomycete H. fragiforme was below 5%, when the samples were treated with 15% AS. The effect of low and moderate AS concentration on the decay resistance was dependent on the fungal strain. The mode of action of AS treatment against basidiomycete decay is discussed.
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December 5, 2007
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This paper describes the hydrothermal treatment (HT) treatment of a mixture of samples treated with three wood preservatives. During HT treatment, creosote-derived hydrocarbon (HC) residues were recovered in the decommissioned treated wood and the wood mass itself was transformed with 95% yield into a mixture of HCs, including substituted benzenes, phenolics and light polyaromatic HCs (PAHs). The metals from the CCA-treated wood were partially recovered (up to 48–88%) either in an acidified AQ phase or as a coating on the internal walls of the reactor. Some arsenic was probably transformed to arsine gas, which could be trapped and recovered under basic conditions. Pentachlorophenol was dechlorinated and removed to below detection limits. The HT process also resulted in the generation of industrially useful mixed HCs with substantial reduction in substrate mass. Thus, the preservative-treated wood as a hazardous waste was transformed into a complimentary mixture of liquid products. Creosote and CCA were recovered, and penta was degraded. It is important to note that this work was performed in large reactors, which were heated with hot air in a muffle furnace. Hence, the incubation time was long. Our current work with small reactors heated instantaneously in tin baths to 400°C has confirmed that HT reactions occur in the order of seconds to minutes. Future publications will address kinetic and mechanistic aspects of these reactions.
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December 5, 2007
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Variation of tracheid length was studied within individual annual rings of Scots pine ( Pinus sylvestris L.) and Norway spruce ( Picea abies (L.) Karst.) from the pith to the bark. The material consisted of six Scots pine and six Norway spruce trees growing on sites of both low and high fertility. Microtome sections of 0.25 mm thick were cut from annual rings 7, 20 and 50 counted from the pith outwards, i.e., juvenile, transition and mature wood, respectively. After maceration, tracheid lengths were separately measured in each sample. In juvenile wood of Scots pine, tracheids were on average 17% longer in the latewood than in earlywood. However, in juvenile wood, the first formed earlywood tracheids were slightly longer than those in the middle of the earlywood zone. In the transition and mature wood of Scots pine, the increase in tracheid length was more gradual from earlywood to latewood, and no significant differences were found between earlywood and latewood. In Norway spruce, tracheids were 2–4% longer in the latewood than in earlywood. In general, tracheid length is highly variable within annual rings and the variation can differ from ring-to-ring even within the same tree.
