Volume 62, Issue 6

Soda and soda-anthraquinone (AQ) pulpings of poplar ( Populus deltoides ) wood performed in a flow-through reactor gives rise to the formation of coniferyl alcohol ( 1 ) sinapyl alcohol ( 2 ) and other low molecular weight (LMW) compounds in different stages of delignification. During the heating-up period, the formation of these compounds increases until the maximum pulping temperature ( t max , 170°C) is reached. Afterward, their concentration in the spent liquor decreases sharply. This effect is accompanied by solubilization of high molecular weight (HMW) lignin fractions. Compared with soda pulping, the soda-AQ pulping shows a higher production of LMW compounds because of the presence of AQ-anthrahydroquinone (AHQ) redox system. During the heating-up period, the formation of 1 and 2 – apparently originated from non-etherified β-aryl-ether moieties in the lignin – is accompanied by solubilization of lignin fragments with relative LMW. Lignin cores, having β-aryl-ether bonds as major hydrolyzable inter-unit linkages, remain in the fiber, and they give rise to solubilized lignin fragments with HMW at later delignification stages. The dissolved fragments, in particular those formed during heating-up period, undergo further degradation in the liquor. The degradation occurs via oligomers at the end of the pulping, while the residual lignin cores are more resistant. Pulps with low kappa number can be produced by maintaining higher alkali concentrations than the usual in the last delignification phase. When the pulping liquor is replaced in this stage with liquors of higher alkali concentration, extended delignification will be the result. As a consequence, less degraded lignin fragments will be deposited on fibers.

Degraded lignin fragments dissolved in pulping liquor during the soda AQ pulping of poplar ( Populus deltoides ) wood with a flow through reactor were divided in two fractions. The first one (LF-1) was collected during the heating-up period (100°C until the final temperature t max =170°C); the second one (LF-2) was collected at t max with 60 min cooking time. These two liquors were then treated at 170°C for 70 min (leading to a liquor LF-1A) and 10 min (leading to a liquor LF-2A). By these post-treatments, pulping liquors of batch pulpings were simulated. From the four liquors, lignins were isolated and after purification the chemical and physical properties were characterized by Gel Permeation Chromatography (GPC: to obtain their molecular weight distribution), nitrobenzene oxidation, permanganate oxidation, and 13 C NMR spectroscopy. By these means, the reaction mechanisms of dissolved and degraded lignin fragments in pulping liquors was elucidated and insight was gained concerning the effectiveness of the anthraquinone-anthrahydroquinone (AQ-AHQ) redox system using the corresponding batch lignin preparation as reference. The simulated batch fractions LF-1A, LF-2A, and true batch lignin preparations are similar. They have a high content of condensed arylpropane units. Among them, syringylpropane units are most severely degraded, in particular, etherified β-aryl ether bonds are cleaved to a great extent after dissolution in pulping liquor. The structure of the remaining degraded lignin fragments was changed seriously, particularly on their side chains. Oxidation and disproportionation reactions are typical. In the presence of fibers, xylans tend preferentially to simple deposition on fibers instead of grafting with the degraded lignin fragments. Dissolution of carbohydrates is not affected by higher alkali concentration at the end of the pulping, and the yield losses are caused by a better lignin removal.

The effect of autohydrolysis of Eucalyptus globulus wood was studied with regard to conditions applied in a prehydrolysis-kraft process on the physico-chemical properties of lignin obtained in both the wood residue and hydrolysate. As a reference, milled wood lignin (MWL) was isolated from native wood and compared to three lignin fractions formed during prehydrolysis: 1) lignin from the wood residue isolated as MWL, 2) lignin precipitated from the prehydrolysate during cooling and separated by centrifugation, and 3) lignin degradation products soluble in the prehydrolysate extracted with ethylacetate. All lignin fractions were subjected to Fourier transform infrared (FTIR) spectroscopy, methoxy group determination, elemental analysis, size exclusion chromatography and quantitative nuclear magnetic resonance (NMR) spectroscopy. The results indicate that extensive lignin degradation occurs during prehydrolysis through homolytic cleavage of the aryl-ether bonds resulting in a substantial molecular weight loss of the residual lignin in the treated wood and in the lignin fractions isolated from the prehydrolysate. The aryl-ether cleavage is coupled with a strong increase in phenolic hydroxyl groups and a decrease in aliphatic hydroxyl groups. Indication for condensation reactions were found by NMR spectroscopy.

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 β-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 β-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.

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.

A method based on FT-Raman spectroscopy is proposed for determining in situ concentrations of ethylenic residues in softwood lignin. Raman contributions at 1133 and 1654 cm -1 , representing coniferaldehyde and coniferyl alcohol structures, respectively, were used in quantifying these units in spruce wood with subsequent conversion to concentrations in lignin. For coniferaldehyde units, the intensity of the 1133 cm -1 peak was measured in the difference spectrum obtained by subtracting 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 concentrations of coniferaldehyde and coniferyl alcohol units in spruce lignin were found to be 3.8% and 3.4%, respectively, and were in good agreement with values determined by conventional techniques. This quantification of the ethylenic residues was based on the Raman intensities 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 concentrations of coniferaldehyde and coniferyl alcohol residues in comparison to wood by 28% and 24%, respectively.

Near infrared spectroscopy (NIRS) combined with multivariate analysis techniques was applied to assess phenol content of European oak. NIRS data were firstly collected directly from solid heartwood surfaces: in doing so, the spectra were recorded separately from the longitudinal radial and the transverse section surfaces by diffuse reflectance. The spectral data were then pretreated by several pre-processing procedures, such as multiplicative scatter correction, first derivative, second derivative and standard normal variate. The tannin contents of sawmill collected from the longitudinal radial and transverse section surfaces were determined by quantitative extraction with water/methanol (1:4, by vol). Then, total phenol contents in tannin extracts were measured by the Folin-Ciocalteu method. The NIR data were correlated against the Folin-Ciocalteu results. Calibration models built with partial least squares regression displayed strong correlation – as expressed by high determination correlation coefficient (r 2 ) and high ratio of performance to deviation (RPD) – between measured and predicted total phenols content, and weak calibration and prediction errors (RMSEC, RMSEP). The best calibration was provided with second derivative spectra (r 2 value of 0.93 for the longitudinal radial plane and of 0.91 for the transverse section plane). This study illustrates that the NIRS technique when used in conjunction with multivariate analysis could provide reliable, quick and non-destructive assessment of European oak heartwood extractives.

The valence band of lignin and sputtered lignin was studied by X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and metastable induced electron spectroscopy (MIES). The corresponding spectra were compared with those from fingerprint molecules, representing the various chemical groups of lignin. The results of this analysis show that valence band spectroscopy, in particular a combination of XPS, UPS and MIES, allows an identification of hydroxyl, methoxy and phenyl groups at the lignin surface.

Aqueous wood extracts from the historic Swedish warship Vasa have been analyzed by 1 H-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.

Degradation of polysaccharides and polyethylene glycol have recently been observed in the wood of the Swedish war-ship Vasa . The signs of degradation are highly correlated to the presence of iron compounds, indicating iron initiated reactions of Fenton type. In order to test this hypothesis pure polyethylene glycol (PEG, M w =1500 u) and prepared oak holocellulose were oxidized by hyddroxyl radicals induced by Fenton's reagent [Fe(II)/H 2 O 2 ] in aqueous solution. The changes in molar weight distribution (MWD) were analysed by MALDI-TOF mass spectrometry and size exclusion chromatography. The changes in MWD were consistent to random scission of the polymers according to statistical simulations. By NMR analysis the main PEG degradation products formed were identified as PEG molecules with different end groups: alcohols, aldehydes and formate esters; the latter hydrolyse to formic acid. The all over results show close similarities to the situation observed in the Vasa wood and strengthen the hypothesis of oxidative degradation initiated by iron compounds in the wood.

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 chemical modification of wood. In the present work, liquid model systems were investigated using compounds that resemble repeating units of lignin to verify whether chemical bonds form between the furfuryl alcohol polymer and wood. Using different NMR spectroscopic techniques we confirmed that these model compounds do form covalent bonds with the polymerising polymer. The results indicate that the furan polymer grafts to lignin, supporting observations in similar studies performed with genuine wood materials.

The forest resources are changing due to fire prevention and depletion of old growth forest. Applications for small-diameter juvenile timber, especially for low-value species, such as ponderosa pine ( Pinus ponderosa ) are needed. In this study, a novel thin wood strand composite of P. ponderosa , 3.2 mm thick, is introduced as a veneer substitute. Optimization was performed for the processing parameters phenol formaldehyde resin content, platen temperature, and the aspect ratio strand length to thickness (L/t). Mean modulus of elasticity and modulus of rupture values of 10.2 GPa and 79.1 MPa, respectively, were obtained with the optimized formulation (5.5% resin, platen temperature 152°C, and aspect ratio of 430). These values were approximately 2–2.5 times higher than the parent small-diameter ponderosa pine lumber. The results indicate that fast-growing low-density species – such as hybrid poplars, or small-diameter timber with predominantly juvenile wood – could potentially be used to manufacture strand veneers of consistent quality with significantly higher strength and stiffness than parent material.

Laminated strand veneer (LSV) is a new engineered wood-strand composite consisting of laminated thin (3 mm) strand veneers (see Part 1 of this study). Advantages include utilization of low-density small-diameter timber, good mechanical properties for structural applications, and the ability to engineer the lay-up of laminates for specific end uses. In the present paper, the feasibility of the concept of engineering laminated composites made of thin strand veneers is scrutinized. Properties of individual strand plies and laminated products manufactured with strand plies were determined and compared with traditional wood composite panel properties and predictions based on the classical lamination theory (CLT). Elastic and strength properties of LSV composites compare favorably with plywood and laminated veneer lumber composites made of veneer, and exceeded those of oriented strand board and particleboard. It was shown that the CLT model was useful in engineering composite lay-ups to give an approximation of LSV composites properties. Strength and stiffness of LSV are 100–150% higher than that of the small-diameter parent wood from which it was formed.

A research project has been conducted to develop structural laminated veneer lumber products from tropical wood, and to evaluate their feasibility for the structural components of wooden houses. As part of this project, we investigated the flexural, in-plane shear, and nail shear properties of laminated veneer board (LVB) manufactured from a combination of falcataria ( Paraserianthes falcataria ) and rubberwood ( Hevea brasiliensis ) for flooring applications. In addition, 11-ply larch ( Larix leptolepis ) and 7-ply radiata pine ( Pinus radiata ) plywood were investigated as controls. Larch plywood, bonded with phenol-based adhesive, showed the best strength properties in bending and shear tests, whereas the 12-ply (28 mm thick) resorcinol-based resin-bonded LVB had the highest ductility in nail shear. The LVB also had better bending and shear properties than radiata pine plywood. In conclusion, falcataria-rubberwood LVB demonstrated good potential to substitute larch plywood and radiata pine plywood in flooring applications.

Impedance spectra were collected from Southern pine ( Pinus spp. ) equilibrated to a moisture content 20% and a saturated condition. Cylindrical graphite electrodes were embedded in the wood so that they met nearly end-to-end along a line parallel to the grain, and impedance properties were characterized as functions of electrode spacing and electrode contact pressure at frequencies between 1×10 -1 and 3×10 5  Hz. The data exhibit a low-frequency tail that can be fit with a Warburg element, indicative of a diffusive motion of charge carriers. Values of the Warburg impedance were compared with previously published data on molar conductivities of endogenous mineral ions in wood. The data suggest that mineral ions are the predominant charge carriers in wood at low frequencies and high moisture contents based on the strong correlation between the Warburg impedance and molar conductivities.

The hygroscopicity and thermodynamic properties of juvenile Pinus sylvestris L. wood taken from the submerged piles of a bridge built in 1903 over the Jiloca River, in Spain, were compared with the corresponding values of juvenile wood of the same species from recently cut trees. The 35°C and 50°C isotherms were plotted and subsequently fitted using the Guggenheim-Anderson-Boer-Dent method, and the isosteric heat of sorption was obtained through the integration method of the Clausius-Clapeyron equation. The isotherms were compared by means of the hysteresis coefficients. Infrared spectra were recorded to study the chemical modifications, and the crystal structure of the cellulose was studied by X-ray diffractograms. The submersion in water resulted in hemicellulose degradation and a decrease in the crystallinity index and the crystallite length, accompanied by a corresponding increase in the proportion of amorphous zones. Owing to this, the equilibrium moisture contents of the water logged wood are higher than in the recent wood, both in adsorption and in desorption. In terms of the thermodynamic properties, the bond energy is higher in the recent wood than in the water logged wood.

Wood-degrading fungi commonly grow in contact with calcium (Ca)-containing building materials and may import Ca and iron (Fe) from soil into forest woody debris. For brown rot fungi, imported Ca 2+ may neutralize oxalate, while Fe 3+ may facilitate Fenton-based degradation mechanisms. We previously demonstrated, in two independent trials, that degradation of spruce by wood-degrading fungi was not promoted when Ca or Fe were imported from gypsum or metallic Fe, respectively. Here, we tested pine wood with lower endogenous Ca than the spruce blocks used in prior experiments, and included a pure gypsum treatment and one amended with 1% with FeSO 4 . Electron microscopy with microanalysis verified that brown rot fungi Serpula himantioides and Gloeophyllum trabeum and the white rot fungus Irpex lacteus grew on gypsum and produced iron-free Ca-oxalate crystals away from the gypsum surface. Wood cation analysis verified significant Fe import by both brown rot isolates in Fe-containing treatments. Wood degradation was highest in Fe-gypsum-containing treatments for all three fungi, although only wood degraded by I. lacteus had significant Ca import. We suggest that Fe impurities may not exacerbate brown rot, and that both brown and white rot fungi may utilize Ca-containing materials.

Indoor wood-decay fungi are economically very important. Approximately half of the total damage caused by indoor fungi in Germany is caused by species of the Coniophoraceae. The sequence of the intergenic spacer (IGS) region of the ribosomal DNA was elucidated with the following fungi of this family: Serpula lacrymans (true dry rot fungus), S. himantioides (wild merulius), Meruliporia incrassata (North American dry rot fungus), Leuco-gyrophana pinastri (mine dry rot fungus), Coniophora puteana (brown cellar fungus), and C. marmorata (marmoreus cellar fungus). The IGS length ranges between 2584 and 3785 bp and consists of the short IGS 1 (253–440 bp), the 5S rDNA (118 bp) and the long IGS 2 (2193–3310 bp). IGS 1 is phylogenetically less informative for the investigated Coniophoraceae species. 5S rDNA is transcribed in the reverse direction. IGS 2 contains extended repeat blocks of copies of different length. Intraspecific length polymorphism as a result of different copy number occurs in M. incrassata and L. pinastri . In combination with previous results, the full-length sequence of the rDNA repeat unit is available for important indoor wood-decay fungi. The various rDNA regions can now be used for future identification of unknown sequences by BLAST and also for phylogenetic studies.