Showing papers in "Holzforschung in 2008"

Extractive composition and summative chemical analysis of thermally treated eucalypt wood

Abstract: Abstract Eucalypt wood (Eucalyptus globulus) was heated in an oven for 2–24 h at 170–200°C and in an autoclave with superheated and saturated steam for 2–12 h at 190–210°C. The chemical composition of untreated wood and thermally treated wood with different mass losses in the range of 1.1–11.9% was studied by summative analysis, and the composition of dichloromethane, ethanol and water extracts was determined by gas chromatography mass spectometry (GC-MS). The hemicelluloses degraded first, mainly regarding the arabinose and xylose moieties. Lignin degraded at a slower rate and cellulose was only slightly affected under severe treatment conditions. The extractive content increased first with heat treatment and decreased later on. Almost all of the original extractives disappeared and new compounds were formed, such as anhydrosugars, mannosan, galactosan, levoglucosan and two C5 anhydrosugars. The most prominent lignin derived compounds were syringaldehyde, syringic acid and sinapaldehyde. The main difference between autoclave and oven treated samples was the appearance of more oxidized extractives for the oven treatment.

Structural characterization of milled wood lignins from different eucalypt species

Abstract: The chemical structure of milled-wood lignins from Eucalyptus globulus, E. nitens, E. maidenii, E. grandis, and E. dunnii was investigated. The lignins were characterized by analytical pyrolysis, t ...

Effect of autohydrolysis of Eucalyptus globulus wood on lignin structure.Part 1: Comparison of different lignin fractions formed during water prehydrolysis

Abstract: Three different levels of autohydrolysis intensity, expressed as the prehydrolysis (P)-factor, were applied to Eucalyptus globulus wood at a liquor/wood ratio of 5:1. Lignin fractions were isolated from the wood residue as milled wood lignin (MWL), from the hydrolysate by centrifugation (insoluble fraction) and by ethyl acetate extraction (soluble fraction), and from the reactor wall as precipitate. With increasing autohydrolysis duration, a decrease in the content of aliphatic hydroxyl groups and of beta-O-4 structures was detected in all lignin fractions, whereas the content of phenolic hydroxyl groups increased in the same order. MWL isolated from wood residue after autohydrolysis at the highest P-factor contained only half the beta-O-4 structures contained in native lignin. Molecular weight distribution measurements revealed that fragmentation reactions dominated over condensation reactions in all lignin samples investigated. However, low-molecular-weight lignin dissolved in autohydrolysate exhibited extremely high reactivity towards acid- catalysed condensation reaction, which inevitably leads to the formation of sticky precipitates during storage at elevated temperature under the acid conditions prevailing.

Extraction of galactoglucomannan from spruce wood with pressurised hot water

Abstract: Abstract Sapwood chips and ground wood of spruce have been extracted with pressurised pure water in an accelerated solvent extractor at temperatures from 100 to 180°C. The water extracts were freeze-dried, weighed, and analysed for carbohydrates by acid methanolysis followed by GC determination of monomeric sugars. Lignin was determined by measuring UV absorption and acetyl groups by HPLC after alkaline hydrolysis. Average molar masses of hemicelluloses in water extracts were determined by HPSEC-MALLS after filtration. Typically, approximately 70% of the total weighed extracts were composed of carbohydrates derived from hemicelluloses. Approximately 75% of the extracted carbohydrates were from galactoglucomannan (GGM). Other extracted substances were xylans, arabinogalactans, lignin and acetic acid. As much as 80–90% of the GGM in the wood, i.e., approximately 15% based on the original wood, was extracted from ground wood at 170–180°C for an extraction time of 1 h. The yields from chips were lower: approximately 60% from that of ground wood. The hemicelluloses were partly hydrolysed during the extractions at 160–180°C. Xylans and arabinogalactans were hydrolysed to a higher extent than GGM. Acetyl groups in GGM were also partly hydrolysed, which resulted in lower GGM solubility. A key factor for achieving a high yield of high-molar mass GGM is an optimised pH profile in order to minimise hydrolysis of acetyl groups and hydrolytic cleavage of GGM chains.

Towards novel wood-based materials: Chemical bonds between lignin-like model molecules and poly(furfuryl alcohol) studied by NMR

Abstract: Wood modification with furfuryl alcohol is a non-toxic alternative to conventional preservation treatments. A process in which furfuryl alcohol polymerises in situ was previously proposed for chemi ...

Cellulose aerogels: Highly porous, ultra-lightweight materials

Abstract: Abstract Cellulosic aerogels are intriguing new materials produced by supercritical drying of regenerated cellulose obtained by solvent exchange of solid Lyocell moldings. From N-methylmorpholine-N-oxide (NMMO) solutions with cellulose contents between 1 and 12%, dimensionally stable cellulose bodies are produced, in which the solution structure of the cellulose is largely preserved and transferred into the solid state, the material having densities down to 0.05 g cm-3 and surface areas of up to 280 m2 g-1. In this study, several aspects of cellulosic aerogel production are communicated: the stabilization of the cellulose solutions against degradation reactions by agents suitable for later extraction and drying, a reliable extraction and drying procedure by supercritical carbon dioxide, the advantages of DMSO/NMMO in this procedure as a solvent/non-solvent pair, and some data on the physical properties of the materials.

Adhesive penetration of wood cell walls investigated by scanning thermal microscopy (SThM)

Abstract: Abstract 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.

Hydrothermal dissolution of mixed southern hardwoods

Abstract: Abstract A hydrothermal dissolution profile of wood components cellulose, hemicelluloses, and lignin of hardwood during autohydrolysis for 100 min at temperatures from 130 to 170°C in a modified accelerated solid extraction system (Dionex ASE-100) is described. The content of cellulose, hemicelluloses, lignin, acetyl, and uronic acid groups remaining in the extracted wood were determined. The extract was analyzed for oligosaccharides and monosaccharides, lignin, acetic acid, uronic acid, furfural, and hydroxymethylfurfural. Xylo-oligomers are the predominant component in the extract at temperatures higher than 150°C. At temperatures higher than 160°C, small amounts of furfural and hydroxymethylfurfural are generated. Most of the arabinan and galactan are removed from the wood at 160°C. The xylan remaining in the wood is acetylated at the same degree as in the original wood. In the extract, the ratio of acetyl groups bound to xylo-oligosaccharides decreases with increasing temperature. The content of uronic acid groups found in the extract obtained after autohydrolysis at T≥150°C is significantly smaller than that calculated from the decrease in uronic content of the wood.

The reduction in the fibre saturation point of wood due to chemical modification using anhydride reagents: A reappraisal

Abstract: The data from a previous study of the moisture adsorption of Corsican pine modified with linear chain carboxylic acid anhydrides, (acetic, propionic, butyric, valeric, hexanoic), has been reanalysed so that moisture content is reported as a percentage of cell wall mass only. As part of this work, the change in fibre saturation point (FSP, determined from fits of the Hailwood Horrobin model) of the modified wood has been determined as a function of weight percentage gain (WPG). The change in FSP is not determined by the extent of hydroxyl substitution of the cell wall, but is related to WPG only (as reported previously). This is also true for the relationship between monolayer water, polylayer water, molecular weight per sorption site at saturation and WPG. However, there is no simple linear relationship between calculated FSP and WPG. When the FSP was determined by solute exclusion methods, the reduction thereof could be simply explained as due to bulking of the cell wall by the bonded acyl substituents. This is not the case when the FSP is determined from adsorption isotherms. This result is interpreted as an ambiguity of determination of FSP from projections of sorption isotherms. Differences in FSP determined by the two methods (sorption versus solute exclusion) are considered to be due to incomplete wetting of the lignocellulosic material when absorbing moisture from the initial dry state.

A new and facile method for isolation of lignin from wood based on complete wood dissolution

Abstract: Abstract 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.

Degradation of polyethylene glycol and hemicellulose in the Vasa

Abstract: Abstract 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.

Pyrolytic cleavage mechanisms of lignin-ether linkages: A study on p-substituted dimers and trimers

Abstract: Abstract Pyrolytic cleavage mechanisms of lignin-ether linkages were studied with some dimers and trimers which have various p-substituted Cα-phenoxy groups (-H, -OCH3, -Cl or -COCH3). 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 Cβ-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 Cβ-O bonds in the phenolic trimers. Electron attracting character of the quinone methide structure reduces the BDE of the Cβ-O bond.

FTIR spectroscopy in combination with principal component analysis or cluster analysis as a tool to distinguish beech (Fagus sylvatica L.) trees grown at different sites

Abstract: FTIR spectroscopy was used to distinguish between beech (Fagus sylvatica L.) trees grown at five different sites; one in middle Germany close to Gottingen (forest district Reinhausen), three located in the southwest (two in Rhineland-Palatinate: forest districts Saarburg and Hochwald, and one in Luxembourg), and one in North- Rhine Westfalia. Detailed investigation of the spectra in the fingerprint region (1800-600 cm-1) revealed 16 dis- tinct peaks and shoulders, most of which were assign- able to wavenumbers previously shown to represent wood compounds. Differences in peak heights and peak ratios indicated differences in wood composition of beech trees from different sites. To determine if the wood of individual trees could be distinguished, principal com- ponent analysis (PCA) and cluster analysis were per- formed using FTIR spectra as input data. With both PCA and cluster analysis, trees from four of the five different sites were separated. It was not possible to distinguish between trees from Saarburg and Hochwald, where sim- ilar edaphic and climatic conditions exist, while wood spectra from trees from all other areas clearly segregat- ed. Wood collected at different positions in the stem (bot- tom, crown, center and outer year rings) of trees grown at the same site was not distinguishable. Therefore, FTIR spectral analysis in combination with multivariate statis- tical methods can be used to distinguish wood of trees from different growth habitats. Extension of this method to other species may be of great interest for wood cer- tification, as it may be possible to distinguish wood, of a given species, originating from different regions.

Plasma treatment of heat treated beech wood - investigation on surface free energy

Abstract: With an increased interest in finding alternatives for tropical timbers and preservative-treated wood, several new wood treatments have recently been commercialised, e.g., acetylation, furfurylation and heat treatment. For the latter, diverse techniques protected by trademarks have been developed, such as the Plato process, retification process, oil-heat treatment, thermo wood and Stellac treatment, whereby the chemical and physical properties of the treated wood are altered (Boonstra et al. 2006a,b). Beneficial changes are the improved dimensional stability and durability which, among other reasons, are caused by the loss of hydroxyl groups which results in reduced hygroscopicity and increased hydrophobicity of surfaces (Tjeerdsma and Militz 2005; Petric et al. 2007). On the other hand, wettability is a prerequisite for good adhesion, but it is reduced by less hydrophilic surfaces after heat treatment. Accordingly, the deposition of waterborne finishes is generally more difficult on heat treated wood (Petrissans et al. 2003; Geradin et al. 2007). Polymer processing industries are using plasma treatment techniques to improve wettability and adhesion on hydrophobic polymer surfaces (Kogelschatz 2003). By plasma treatment, the O/C ratio is increased by the formation of hydroxyl and carboxyl groups which brings about an increase in surface polarity (Jie-Rong et al. 1999; Drnovska et al. 2003) and may be able to compensate partly the loss of functional groups by heat treatment. Several publications deal with plasma treatment of wood or wooden materials for hydrophilicity increment: elevated surface free energy and an ameliorated wetting behaviour with water were found (Rehn and Viol 2003; Rehn et al. 2003; Evans et al. 2007; Toth et al. 2007; Wolkenhauer et al. 2007a,b,c). In general, air, nitrogen or oxygen are the gaseous media to increase hydrophilicity; however, plasma techniques can also be applied for this purpose, i.e., to decrease hydrophilicity. For example, in the presence of special chemicals or reactive gases (e.g., HMDSO, silane) thin layers can be deposited on wood surfaces for creating water repellent characteristics (Denes et al. 1999; Bente et al. 2004; Odraskova et al. 2007). Podgorski et al. (2000) investigated the wetting behaviour of water on heat treated wood after application of oxygen plasma treatment at low pressure (0.08 mbar) and found a significant decrease of water contact angles. To explore the surface modification by plasma treatment in more detail, the surface free energy and the work of adhesion based on the Lifshitz-van der Waals/acidbase approach were determined (Van Oss et al. 1988). In this approach, the total surface energy is divided into (1) a polar or acid-base component, and (2) a dispersive or Lifshitz-van der Waals component. The polar part is further subdivided into an acid part (electron acceptor) and a basic part (electron donor) with regard to the Lewis acid-base model. The latter includes hydrogen bonding, whereas the disperse part or the Lifshitz-van der Waals part comprises London, Keesom and Debye interactions. In the present study, a dielectric barrier discharge (DBD) was used for plasma treatment of heat treated wood. DBD was performed at atmospheric pressure and ambient air to avoid the impact of low pressure.

Revisiting the mechanism of β-O-4 bond cleavage during acidolysis of lignin. Part 1: Kinetics of the formation of enol ether from non-phenolic C6-C2 type model compounds

Abstract: Abstract The reaction route of a dimeric non-phenolic C6-C2 type lignin model compound, 2-(2-methoxyphenoxy)-1-(3,4-dimethoxyphenyl)ethanol (VIII), was kinetically examined under acidolysis conditions (0.2 mol l-1 HBr in 82% aqueous 1,4-dioxane at 85°C). The disappearance of (VIII) followed the pseudo-first-order rate law, and the rate constant k (VIII) was 0.00854. In the course of the reactions, the following compounds were produced quantitatively at any time: an enol ether, 1-(2-methoxyphenoxy)-2-(3,4-dimethoxyphenyl)ethylene (IX), 2-methoxyphenol (X), and a Hibbert's ketone, 3,4-dimethoxyphenylacetaldehyde (XI). The substances (X) and (XI) are the result of the β-O-4 bond cleavage and their amounts were always equal during the whole reaction. When (IX) was subjected to the acidolysis under the identical conditions, its disappearance followed the pseudo-first-order rate law, and the rate constant k (IX) was 0.00825. Furthermore, (VIII) was not observed at all, and (X) was produced quantitatively at any time. Based on these results, the formation rate of (IX) during the acidolysis of (VIII) is expressed by the equation: d[(IX)]/dt=A·k (VIII)[(VIII)]-k (IX)[(IX)], where A is the proportion of (VIII) that converted into (IX) when (VIII) degraded. It was confirmed by solving this differential equation that the formation and disappearance of (IX) is best simulated when A was assumed to be 1.00. Therefore, it was proven in this paper for the first time that (VIII) primarily converts into (IX), and subsequently the β-O-4 bond cleavage occurs and (X) and (XI) are yielded.

Analysis of acids and degradation products related to iron and sulfur in the Swedish warship Vasa

Abstract: Abstract Aqueous wood extracts from the historic Swedish warship Vasa have been analyzed by 1H-NMR spectroscopy, ion chromatography, and matrix assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry as part of studies on the chemical degradation related to increased levels of iron and sulfur. The results show that low molecular organic acids have accumulated in the Vasa wood after the 1961 salvage. The increased acidity was found in a context of chemical degradation of the wood polymers and the conservation agent polyethylene glycol (PEG) in iron-rich parts of the timber. Formic, glycolic and oxalic acid are all possible end-products of oxidative degradation of wood polymers, whereas hydrolysis of acetyl groups in xylan may have contributed to increased concentrations of acetic acid. MALDI-TOF spectra of PEG displaced towards low-molecular PEG oligomers, as reported earlier, were accompanied by increased levels of formic acid, indicating oxidative degradation of PEG. PEG with a carboxylic acid end group (PEGC) was observed to a minor degree in the wood. However, analysis of stored conservation treatment solutions showed high concentrations of PEGC yielding significant contributions to the acidity during the 1960s conservation period. PEGC was probably formed as a result of microbial processes during the early conservation regime. Calculations using concentrations and well-established acidity constants show that oxalic and formic acid are the primary contributors to a low pH in the wood. The increased acidity in the interior of the wood was found in the absence of sulfur compounds but in a context of iron. The majority of the sub-samples with significant levels of sulfate in the surface region with a prospective sulfur oxidation, however, showed neither a decreased pH nor significant depolymerization. This indicates that oxidation pathways of organically bound sulfur do not necessarily produce strong acids, and thereby free protons, as the final product. These observations imply opposing effects of iron and reduced sulfur species, with iron acting as a initiator in oxidative reactions of Fenton type, whereas the reduced organic sulfur compounds may act as anti-oxidants.

Developing environmentally benign and effective organic wood preservatives by understanding the biocidal and non-biocidal properties of extractives in naturally durable heartwood

Abstract: Abstract Wood products for exterior residential applications have long been protected with metallic preservatives. However, environmental and disposal concerns and governmental regulations have resulted in a growing trend to employ organic systems based on relatively benign and expensive agrochemicals. To develop organic preservatives that have increased efficacy and lower cost, various groups are studying the biocidal and non-biocidal properties of extractives present in naturally durable heartwoods. In this study, we determined the fungicidal, free radical scavenger/antioxidant, metal chelation and Fe3+ reducing properties of some flavones and flavonoid analogs and chromones. The results support our earlier hypothesis that the abiotic antioxidant, Fe3+ reduction and subsequent metal complexation properties, in combination with the extractives’ fungicidal properties, all have a role in natural durability. Consequently, it may be possible to employ non-biocidal additive(s) with the above abiotic properties to enhance the efficacy of the relatively expensive organic agrochemicals used to protect wood.

Isolation and characterization of lignins from Eucalyptus grandis Hill ex Maiden and Eucalyptus globulus Labill. by enzymatic mild acidolysis (EMAL)

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 31P NMR, DFRC/31P NMR (derivatization followed by reductive cleavage followed by quantitative 31P 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-b-aryl ether structures, free phenolic hydroxyl groups and syringyl-type units than lignin from E. grandis. New insights provided by the DFRC/31P NMR revealed that up to 62.2% of arylglycerol-b-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.

Determination of ethylenic residues in wood and TMP of spruce by FT-Raman spectroscopy

Abstract: A method based on FT-Raman spectroscopy is proposed for determining in situ concentrations of ethylenic resi­ dues in softwood lignin. Raman contributions at 1133 and 1654 cm-1, representing coniferaldehyde and coni­ feryl alcohol structures, respectively, were used in quan­ tifying these units in spruce wood with subsequent conversion to concentrations in lignin. For coniferalde­ hyde units, the intensity of the 1133 cm -1 peak was measured in the difference spectrum obtained by sub­ tracting the bleached-wood spectrum from that of the unbleached. In the case of coniferyl alcohol residues, the intensity of the 1654 cm -1 band was calculated from the spectrum of extensively bleached wood. The concentra­ tions of coniferaldehyde and coniferyl alcohol units in spruce lignin were found to be 3.8% and 3.4%, respec­ tively, and were in good agreement with values deter­ mined by conventional techniques. This quantification of the ethylenic residues was based on the Raman inten­ sities of 1% coniferaldehyde and 1% coniferyl alcohol in bleached softwood kraft pulp. Initially, as background for this work, a number of suitable lignin model compounds and a softwood lignin model polymer (G-DHP) were used to calibrate the Raman method and demonstrate that the Raman technique was well suited for quantification of ethylenic structures. Experimental results demonstrated that thermomechanical pulping reduced the concentra­ tions of coniferaldehyde and coniferyl alcohol residues in comparison to wood by 28% and 24%, respectively.

Topochemical investigation on tension wood fibres of Acer spp., Fagus sylvatica L. and Quercus robur L.

Abstract: Topochemical detection of lignin and phenolic compounds was carried out at subcellular level in tension wood fibres of maple (Acer spp.), beech (Fagus sylvatica) and oak (Quercus robur) by means of cellular UV-microspectrophotometry (UMSP) and confocal Raman microscopy. UMSP field scans at 278 nm revealed the presence of aromatic compounds in the gelatinous layer (G-layer) in tension wood of all three species. Characterisation of the detected substances by point measurements from 240 nm to 400 nm revealed a plausible relationship to by-products from the lignin biosynthesis pathway. Raman spectra, recorded from different regions within the G-layer, showed a high affinity to spectra of lignins. The degree of aromatic compounds in the G-layer of oak tension wood fibres was approximately three-fold higher than that in maple and beech. Moreover, the oak G-layer showed an accumulation of aromatic compounds towards the cell lumen up to 50% higher than that detected in the secondary cell wall. UMSP and Raman microscopy are considered valuable complementary methods for topochemical investigation on a subcellular level.

Laccase-catalyzed functionalization with 4-hydroxy-3-methoxybenzylurea significantly improves internal bond of particle boards

Abstract: Abstract Enzymatic functionalization is an attractive tool to provide a reactive interface for further processing of lignocellulosic materials, such as wood particles and fibers. Here, spruce wood particles have been functionalized by fungal laccase combined with 4-hydroxy-3-methoxy-benzylamine (HMBA) or 4-hydroxy-3-methoxybenzylurea (HMBU). The expectation was crosslinking with resins in subsequent glueing processes, which should improve strength properties of particle boards. Essential process parameters, such as liquid to solid mass ratio and treatment time, were optimized on a laboratory scale resulting in HMBA and HMBU binding yields of 90% and above as determined by radiochemical mass balance analysis. We employed a multifactorial experimental design for board production from treated wood particles and urea/formaldehyde resin. Mechanical testing and multivariate data analysis revealed, for the first time, an increase of internal bond (IB) as a result of functionalization with HMBU. HMBA was not successful. Variance analysis of relevant parameters and their interactions demonstrated a highly significant difference (P>99.99%) between boards treated with laccase/HMBU versus untreated wood particles. Due to positive interactions, functionalization was most effective at high bulk density (750 kg m-3) and high resin content (10%) resulting in a calculated IB improvement of 0.12 N m-2 (21%).

Decay resistance of wood treated with amino-silicone compounds

Abstract: Abstract 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.

Characterisation of fines from unbleached kraft pulps and their impact on sheet properties

Abstract: Fines are an essential component in the papermaking process because they have a profound influence on the behaviour of the wet web and on the mechanical properties of the final sheet. Primary fines ...

Effect of thermo-mechanical refining pressure on the properties of wood fibers as measured by nanoindentation and atomic force microscopy

Abstract: Refined wood fibers of a 54-year-old loblolly pine (Pinus taeda L.) mature wood were investigated by nanoindentation and atomic force microscopy (AFM). The effect of steam pressure, in the range of 2–18 bar, during thermomechanical refining was investigated and the nanomechanical properties and nano- or micro-level damages of the cell wall were evaluated. The results indicate that refining pressure has important effects on the physical and mechanical properties of refined fibers. No obvious damage was observed in the cell walls at pressures between 2 and 4 bar. Nano-cracks (most less than 500 nm in width) were found in fibers at pressures in the range of 6–12 bar, and micro-cracks (more than 5 m mi n width) were found in fibers subjected to pressures of 14 and 18 bar. The damages caused at higher pressures were more severe in layers close to the lumen than on the fiber surfaces. Under special circumstances, the S3 layer was heavily damaged. The natural shape of the cross sectional dimensions of the cell walls was not changed at lower pressures (2 and 4 bar), but, as pressure was increased, the fibers tended to collapse. At pressures around 18 bar, the lumina were augmented again. The nano-mechanical properties in terms of elastic modulus and hardness were obviously decreased, while nanoindentation creep increased with refining pressure.

Polysaccharide degradation in waterlogged oak wood from the ancient warship Vasa

Abstract: 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 lithi ...

UV resonance Raman spectroscopic study of photodegradation of hardwood and softwood lignins by UV laser

Abstract: Abstract The effect of laser irradiation (Ar+ ion laser, 244 nm) on photodegradation of lignin in silver birch and rubberwood as hardwoods and spruce and chir pine as softwoods has been investigated by UV resonance Raman spectroscopy (UVRRS). UVRR spectra showed degradation of aromatic structures accompanied by the formation of both ortho- and para-quinone structures as a result of photodegradation of wood surfaces. There was a rapid decrease in the intensities of all the lignin-associated bands accompanied by broadening of aromatic bands at 1602 cm-1 and in the region of 1500–1000 cm-1 due to formation of unsaturated structures arisen from lignin degradation. The rate of lignin degradation was observed by measuring the relative intensity of aromatic band at 1602 cm-1 during photodegradation. The rates of UV-degradation of hardwood and softwood surfaces were compared and it was found that hardwoods degrade at a faster rate than softwoods. The syringyl structures in hardwood lignin are more sensitive to photochemical degradation than guaiacyl structures. The rate of photodegradation increased with increasing intensity of the irradiated laser energy.

1-Alkoxymethyl-X-dimethylaminopyridinium-base ionic liquids in wood preservation

Abstract: Abstract The following pyridinium-based ionic liquids (ILs) have been successfully tested as components of potential wood preservatives: 1-alkoxymethyl-3-dimethylaminopyridinium chlorides, 1-alkoxymethyl-4-dimethylaminopyridinium chlorides, 1-alkoxymethyl-3-dimethylaminopyridinium acesulfamates and 1-alkoxymethyl-4-dimethylaminopyridinium acesulfamates. These ILs are new biocides that penetrate well into wood. The tested pyridinium ILs with an alkoxymethyl substituent, consisting of 8, 9 or 10 carbon atoms, exhibited fungicidal activity against the basidiomycetes Coniophora puteana and Trametes versicolor and the blue-stain fungus Sclerophoma pityophila. The effective and lethal doses were measured by the agar-plate method and the toxic values, before and after leaching according to EN 84, were determined based on the EN 113 block method. The doses and toxic values of tested 1-decyloxymethyl-4-dimethylaminopyridinium chloride and acesulfamate were comparable with benzalkonium chloride and didecyldimethylammonium chloride. The ILs tested were largely unleachable from wood by water. The mechanical properties of wood treated with the former two ILs were lower than natural wood. Wood treated with the chloride and acesulfamate was, however, characterized by lower absorption of free water than the control wood. Only in the case of treatment with acesulfamate was the hygroscopicity of treated wood distinctly lower than that of control wood. The durability of wood was increased by 1-decyloxymethyl-4-dimethylaminopyridinium chloride and acesulfamate.

Structure elucidation of phenylethanoid glycosides from Paulownia tomentosa Steud. var. tomentosa wood

Abstract: Paulownia tomentosa Steud. var. tomentosa (Scrophulariaceae), a variety of Paulwownia tomentosa Steud., is a large deciduous tree indigenous in China and widely distributed in Eastern Asia; it is usually 10–20 m tall, with strong branches. It blooms in May and June, before the leaves appear. The flowers are white to light purple in color. The fruit is a double-capsuled, red-brown ligneous seed ball, approximately 4 cm long. The fruit ripens in autumn and after bursting many winged seeds are set free. The leaves of the variety are densely hairy, which distinguishes it from the sparse haired leaves of Paulwownia tomentosa Steud. (Hong et al. 1998; Smejkal et al. 2007). In traditional medicine, the bark, wood, fruit and leaf of the plant are used to treat cough, bronchitis, hemorrhoid, asthma, high blood pressure and bacterial diarrhea (Jiang 2003). Chemical constituents of P. tomentosa Steud. var. tomentosa have never been reported, to date, though its medicinal properties are well known. From the Paulownia species, several classes of characteristic secondary metabolites have been isolated, including lapachol type naphthoquinones (Huang et al. 2004), phenylpropanoid glycosides (Ota et al. 1993; Kang et al. 1994), iridoids (Damtoft and Jensen 1993) and lignans (Takahash and Nakagawa 1966; Ayres and Loike 1990; Okazaki et al. 1997; Huang et al. 2004; Silvestre et al. 2005). In our previous paper concerning the aqueous acetone extract of the Paulownia coreana inner bark, we identified three epimeric phenylpropanoid glycosides, cistanoside F, campneoside II and isocampneoside II (Kim et al. 2007). This work is a report on the purification and elucidation of a novel phenylethanoid glycoside (4), together with three that are known: verbascoside (1), isoverbascoside (2) and campneoside I (3).

Evaluation on structural performance of compressed wood as shear dowel

Abstract: Abstract This study addresses the application of compressed wood (CW) made of Japanese cedar, as a substitute for high-density hardwood, to shear dowel. A double wood-to-wood shear test was performed to evaluate the mechanical shear properties of CW perpendicular to the grain, and the results were compared with those of several types of dowel material. CW with its annual ring radial to loading direction (0°) had a unique double shear performance characteristic, and showed good properties as a dowel material by virtue of its strength and rich ductility. In contrast, CW with its annual ring tangential to loading direction (90°) and maple exhibited brittle failure. While thickness of the base member was varied, the ductility of the joint became stable for diameter over 36 mm and 24 mm thickness for the main and side members, respectively. When the density of the base member increased, its stiffness, yield load, and maximum load exhibited proportional improvement with different inclinations; however, in the case of a maple dowel, the increases were small. When the density of the base member was increased, the ultimate load had positive linear tendency, whereas plastic modulus decreased. Consequently, almost constant energy absorption was observed in spite of the increased density. The optimum load-carrying capacity and ductility of a compressed wooden dowel joint could be designed by introducing an appropriate base member.

Laboratory screening of tropical hardwoods for natural resistance to the marine borer Limnoria quadripunctata: The role of leachable and non-leachable factors

Abstract: 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 leachingresistant 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.