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August 8, 2007
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August 8, 2007
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Woods of 36 tree species from the Brazilian Amazon forest have been extracted and analyzed by means of total hydrolysis. For each species, three trees were analyzed in duplicate. The sugars and other byproducts of hydrolysis were analyzed by HPLC. Uronic anhydrides and acid-soluble lignin were determined by colorimetric methods. Acid-insoluble lignin, ash, and extractive contents were analyzed gravimetrically. Each analysis was performed several times and the data were evaluated statistically. The average percentages for ash and extractives are presented. Quantitative data for sugars obtained by HPLC were recalculated for glucan, galactan, arabinan, and mannan contents. These data are presented together with quantitative data for acetyl groups, 5-hydroxymethyl-2-furfuraldehyde, levulinic acid, uronic anhydride, acid-soluble and -insoluble lignin as summative analysis data based on an ash- and extractive-free basis, where, in an ideal case, the data should sum up to 100%. The summative results obtained varied from 96.0% to 99.6%, which is very satisfactory.
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August 8, 2007
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The amount of non-cellulosic glucans in Eucalyptus globulus wood (approx. 4.5%) was assessed by extraction of sawdust with a 0.5 M NaOH solution at 90–120°C and the structural features were elucidated in a glucan-enriched polysaccharide fraction isolated by hot water extraction (120°C, 2 h). Isolated soluble glucans were characterized by wet chemistry methods and a set of 1D and 2D NMR techniques. The major proportion of glucans consisted of amylose (20%) and amylopectin (80%), although a small proportion of β-(1→3)-glucan (<0.2% on wood weight) was also detected. Although glucans are easily removed in the initial phase of kraft pulping, notable amounts were found in unbleached pulp and it was supposed that in the final stage of kraft pulping a fraction of α-glucan is precipitated onto the fiber surface and contributes to the pulp yield.
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August 8, 2007
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The formation of phenolic compounds during pretreatment of sugarcane bagasse was investigated. Bagasse was pretreated by wet oxidation (WO) at 195°C during 15 min under either alkaline or acidic conditions and by steam explosion (STEX) at 205°C during 10 min. The total content of phenolic compounds in the prehydrolysates was determined spectrophotometrically. Under acidic and alkaline WO conditions, 3.8% (w/w) and 3% phenols were found, respectively. STEX gave rise to 1.9% phenols. Individual phenols were identified by GC-MS. Phenylpropanoid derivatives, such as p -coumaric and ferulic acids, accounted for more than 50% of the phenols identified in STEX prehydrolysates. In WO prehydrolysates, on the other hand, phenols lacking the propanoid side chain were predominant. Of the latter, p -hydroxybenzaldehyde was the most abundant phenol, with concentrations of 0.27% (acidic conditions) and 0.15% (alkaline conditions). As expected, high concentrations of oxidised compounds were generally observed in WO prehydrolysates, such as carboxylic acids, aldehydes and ketones. This is a true reflection of the oxidative conditions during WO pretreatment.
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August 8, 2007
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A new approach based on hydrogen-deuterium exchange is proposed for measuring accessible OH groups in wood. The deuterium (D) exchanged for hydrogen in OH groups in wood was converted to D 2 O by combustion in oxygen gas then diluted in deionized water, and subsequently determined by 2 H NMR spectroscopy. The amount of accessible OH groups in Styrax tonkinensis wood is approximately 6.8 mmol g -1 . This measurement is very accurate, with an error of approximately 0.2 mmol g -1 . Heat-treated wood has a lower amount of accessible OH groups than non-treated wood. This finding is in agreement with the decreased hygroscopicity of heat-treated wood and explains, at least partially, its increased fungal resistance.
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August 8, 2007
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Commercial softwood kraft pulp with kappa number 30.5 (KP 30.5 ) was delignified with polyoxometalates (POM, Na 5(+2) [SiV 1(-0.1) MoW 10(+0.1) O 40 ]), and POM-treated kraft pulp of kappa number 23.6 was obtained (KP POM,23.6 ). Residual lignin from pulps was isolated by mild acid hydrolysis and characterized by analytical and spectral methods to gain insight into lignin reactions taking place during the initial delignification phase. Lignin from POM-delignified pulp was isolated in lower yield. Comparative analysis of residual lignins (RL-KP 30.5 , RL-KP POM,23.6 ) showed that POM leads to products enriched in carbonyl/carboxyl groups and carbohydrates. POM lignins have a lower molecular mass and a lower content of phenolic hydroxyl and methoxyl groups. Based on these results and FTIR spectra, we suggest that aromatic ring cleavage and quinone formation occur during POM delignification. The degree of lignin-cellulose association increases after POM delignification. Lignin-cellulose association was found to be partially unstable under mild alkaline conditions, as residual lignin isolated after alkaline extraction of KP POM,23.6 pulp (RL-KP POM/NaOH ) exhibited lower glucose content, higher Klason lignin content, and less extraneous material.
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August 8, 2007
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A light-colored rosin glycerol ester was synthesized from gum rosin and glycerol in the presence of a highly effective decolorizing agent. The effects of the type and dosage of the decolorizing agent and the reaction temperature and time on the yield, softening point, color, and acid number of the rosin glycerol ester were investigated. Experimental results showed that 4,4′-thio-bis(6- tert -butyl-3-methyl phenol) was the best decolorizing agent. It promoted esterification at an optimal dosage of 0.5% (based on the weight percentage of starting material rosin). Suitable conditions for esterification of rosin and glycerol were: reaction temperature, 260–270°C; reaction time, 6–8 h; and rosin/glycerol molar ratio, 2.5:1 (mol mol -1 ). The characteristics of the rosin glycerol ester obtained under these conditions were as follows: softening point, 90–94°C (ball and ring method); color, 1–2 (Gardner value); acid number, 7–8; and yield, >88% (based on the total weight of rosin and glycerol). The selected additive has a multifunctional effect involving bleaching, disproportionation, and catalysis.
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August 8, 2007
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Steady-state fluorescence emission spectra of various celluloses were measured at an excitation wavelength of 320 nm. Various spectra recorded in the solid state were compared: (1) ECF bleached papers made of hardwood, the anhydroglucose units of which were chemically modified at C 1 and C 6 or C 2 and C 3 positions with carboxylic groups; (2) microcrystalline cellulose; (3) cotton linters; and (4) delignified sisal fibers (mercerized or not). Fluorescence emission was quite independent of the carboxylic acid content and average molecular weight (determined by viscosimetry) of the cellulose polymers. Microcrystalline cellulose (Avicel), cotton linters, and mercerized delignified sisal cellulose were acetylated in homogeneous medium (DMAc/LiCl as solvent system) to obtain soluble polymers in dichloromethane for comparison of spectra recorded in the solid and liquid states. Fluorescence of cellulose acetates in solution (CH 2 Cl 2 ) and in the solid state was compared under similar experimental conditions to non-esterified celluloses in the solid state. The importance of the solid state for fluorescence emission could be demonstrated. Fluorophores are present in minute amounts in the polymer and their favorable energy transfer for excitation in the solid state likely enhances fluorescence emission. Among numerous fluorophores, dityrosine appeared to be a good candidate for fluorescence because it displayed emission in the fluorescence range of cellulose. Dityrosine is an amino acid involved in the lignification of non-woody plants. Mercerized sisal impregnated with tyrosine in the presence of peroxidase and hydrogen peroxide did not show enhanced emission, in contrast to para -hydroxycinnamic acid (coumaric acid), which is also involved in the lignification process at least for non-woody plants. The origin of cellulose fluorescence remains uncertain and appears to have several origins. This study clearly underlines the importance of the solid state for enhancing fluorophore emission.
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August 8, 2007
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Fluorescence techniques are highly sensitive and, since aromatic lignin is the most likely source of natural pulp fluorescence, they are suitable for detailed investigation of residual lignin in bleached pulps. Such investigations are important to our understanding of the bleachability and brightness reversion of pulps. In this study, the effect of bleaching on pulps was evaluated using fluorescence spectra of two softwood kraft pulps bleached in six elemental chlorine-free and totally chlorine-free sequences. Fluorescence spectra were recorded in each bleaching stage using four different instrument settings. In general, pulp fluorescence at excitation wavelengths of 270 and 350 nm increased as bleaching proceeded. Below a certain lignin content, however, pulp fluorescence measured at an excitation wavelength of 430 nm decreased with the residual lignin content. Carbonyl groups have a quenching effect on fluorescence, and the formation of carbonyl groups after oxygen and ozone delignification induced a decrease in pulp fluorescence. The increase in pulp fluorescence after peroxide bleaching stages was due to the removal of carbonyl groups. Reactions of chromophores during brightness reversion also had an effect on pulp fluorescence. These findings demonstrate that fluorescence spectroscopy provides an interesting tool for pulp bleaching studies.
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August 8, 2007
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To obtain more knowledge of the properties affecting print quality and adhesion characteristics in the printing process, attention has been directed to the nature of surface energy. The aim was to compare different surface-energy calculation models and to investigate the influence of surface roughness on wetting of coated offset papers. The wetting process was studied by static contact angle measurements using a series of reference liquids. Topographical characterization was carried out using atomic force microscopy. Surface energy components were determined using different calculation models. The determination can be considerably simplified using a mono-monopolar model, which has been proven in previous studies. The surface energy components were derived from both apparent and topography-corrected contact angles. The surface topography had a significant effect on wetting of the samples studied.
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August 8, 2007
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Metastable induced electron spectroscopy (MIES), ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were applied to study the interaction of Ti metal atoms with spruce surfaces. Spruce surfaces were produced by planing splints from a spruce bar. Ti atoms were adsorbed from a metal evaporator under ultra-high vacuum conditions. The amount adsorbed corresponds to 10 monolayer equivalents. Strong interactions between the spruce surface and metals atoms occurred. Impinging Ti atoms were oxidized by the spruce surface. No Ti agglomeration or particle formation was observed. The surface was smoothed by the Ti applied and was completely covered by a titanium oxide film.
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August 8, 2007
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Paper made of groundwood was surface treated by atmospheric plasma of the diffuse coplanar surface barrier discharge (DCSBD) type in air and in nitrogen. Changes in surface composition and chemical bonding of the constituent elements were studied by X-ray photoelectron spectroscopy (XPS), and alterations in wetting were examined by contact angle measurements. Air plasma treatment resulted in strong oxidation but no N incorporation, while the ratio of the area of the O1 component (binding energy 532.1 eV) to that of the O2 component (533.2 eV) decreased, reflecting an increase in the proportion of O in C–O type bonds. Nitrogen plasma treatment followed by exposure to the atmosphere resulted in a slight N incorporation (1.5 at.%) and oxidation even more intense than observed for air plasma treatment. The O1/O2 ratio slightly increased, implying more O in C=O type bonds. The time dependence of surface oxidation showed a local maximum at treatment time of approximately 2 s for both the air and nitrogen plasmas.
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August 8, 2007
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A study was performed on stone groundwood (SGW) pulps produced on a pilot scale. The behaviour of selected juvenile and mature Norway spruce wood samples was investigated. As revealed by standard tests, sheets formed from juvenile wood showed improved light scattering properties, improved tear and tensile strength, and higher sheet density compared to those formed from mature wood. Scanning electron microscopy indicated that the differences are likely related to the manner of fibre processing and development at the ultrastructural level. Mature wood fibres showed greater fibre end breakage, a smaller long-fibre fraction, enhanced S1 fibrillation and frequently open fibres. In contrast, juvenile fibres had a 14% higher long-fibre fraction and showed typical S2 fibrillation. Fibre development of juvenile wood showed fibrillation features similar to those previously reported for thermomechanical pulp fibres. In both cases, the structural hierarchy of the wood fibre cell wall and the microfibril angle of S2 and S1 layers govern cell-wall splitting and fibrillation progression. The superior quality of the fibre furnish prepared from juvenile fibres compared to mature fibres with SGW pulping may offer an alternative process for more effective utilisation of raw materials such as top logs rich in juvenile wood.
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August 8, 2007
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Stabilization of peracetic acid (PAA) by aspartic acid diethoxy succinate (AES) was studied by electron spin resonance, UV/Vis spectroscopy, electrospray ionization time-of-flight mass spectrometry and oxygen evolution measurements. The results indicate that Mn(II)-AES complexes may exist in both monomeric and dimeric forms. Dimerization is proposed to proceed via formation of an oxygen bridge between two Mn(II)-AES complexes. The equilibrium between these two forms depends strongly on pH, the monomeric form being favored under acidic conditions, while conditions close to neutral pH favor the dimeric form. In the presence of PAA, the dimer form was oxidized and finally yielded MnO 2 . Oxygen evolution measurements were carried out to demonstrate the efficiency of AES in stabilizing PAA solutions containing small amounts of Mn(II) impurities under acidic conditions.
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August 8, 2007
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Stabilization of aqueous H 2 O 2 solutions containing small amounts of transition metal impurities [e.g., Mn(II) and Fe(II)] was studied in terms of UV/Vis and electron spin resonance spectroscopy and oxygen concentration measurements at pH ∼11. The results show that aspartic acid diethoxy succinate (AES) could stabilize H 2 O 2 solutions when Mn(II) and Fe(II) were present. Diethylenetriamine pentaacetic acid (DTPA) showed similar behavior, but was not able to stabilize the solutions as efficiently as AES. In the long-term regime, Na-poly-alpha-hydroxy-acrylate was almost as effective a stabilizing agent as AES. Na-acrylate-3-allyloxide-2-hydroxy propane Na-sulfonate copolymer (Aqualic) could decrease H 2 O 2 decomposition by one order of magnitude, but it was the least efficient stabilizing agent among the substances studied. Furthermore, generation of superoxide radical was not suppressed in the presence of Aqualic.
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August 8, 2007
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The viscoelastic properties of wood have been investigated with a dynamic mechanical analyser specifically developed for wooden materials, the WAVE T device. Measurements were carried out on four wood species in the temperature range 0–100°C at frequencies varying between 5 mHz and 10 Hz. Wood samples were tested under water-saturated conditions in the radial and tangential directions. As expected, the radial direction always revealed a higher storage modulus than the tangential direction. Great differences were also observed in the loss factor. The tanδ peak and internal friction were higher in the tangential than in the radial direction. This behaviour is attributed to the fact that anatomical elements act as a function of the direction. The viscoelastic behaviour of reaction wood differs from that of normal or opposite wood. Compression wood of spruce, which has a higher lignin content, is denser and stiffer in transverse directions than normal wood, and has a lower softening temperature ( T g ). In tension wood, the G-layer is weakly attached to the rest of the wall layers. This may explain why the storage modulus and softening temperature of tension wood are lower than those for opposite wood. We also demonstrate that the time-temperature equivalence fits only around the transition region, i.e., between T g and T g +30°C. Apart from these regions, the response of wood reflects the combined effects of all its constitutive polymers, so that the equivalence is no longer valid.
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August 8, 2007
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Thermoforming of wood veneers into profiles is a novel idea and the focus of this paper is to study the formability characteristics of thin radiata pine ( Pinus radiata D. Don) veneers, which are generally used as surface coverings. Radiata pine is well suited as a raw material for furniture, joinery, and interior architectural products. This is because it has excellent turning, shaping, and laminating properties and readily achieves brilliant stain and paint finishes. In this study, radiata pine veneers were softened by immersion in a hot water bath and then thermoformed by means of heated dies/moulds. The formability characteristics were investigated by conducting single-curvature V-bending tests. The influence of the forming method on the shape conformance of softened veneers under single- and multiple-bend conditions was examined. The paper also discusses the influences of manufacturing parameters that include the softening method, the die temperature, the duration of forming, the ratio of bend radius to veneer thickness, and the veneer architecture. The study clearly establishes the feasibility of forming veneers into multi-bend products in a semi-continuous manner using matched dies.
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August 8, 2007
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This paper presents a study and a refinement of the sorption rate model in a so-called multi-Fickian or multi-phase model. This type of model describes the complex moisture transport system in wood, which consists of separate water vapor and bound-water diffusion interacting through sorption. At high relative humidities, the effect of this complex moisture transport system becomes apparent, and since a single Fickian diffusion equation fails to model the behavior, it has been referred to as non-Fickian or anomalous behavior. At low relative humidities, slow bound-water transport and fast sorption allow a simplification of the system to be modeled by a single Fickian diffusion equation. To determine the response of the system, the sorption rate model is essential. Here the function modeling the moisture-dependent adsorption rate is investigated based on existing experiments on thin wood specimens. In these specimens diffusion is shown to be negligible, allowing a separate study of the adsorption rate. The desorption rate has been observed to be slower at higher relative humidities as well, and an expression analogous to the adsorption rate model is proposed. Furthermore, the boundary conditions for the model are discussed, since discrepancies from corresponding models of moisture transport in paper products have been found.
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August 8, 2007
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Experimental results obtained from maritime pine ( Pinus pinaster Ait.) wood are presented for the characterisation of all LR=(1,2) orthotropic stiffness parameters of clear wood specimens by a single test. The approach relies on application of the virtual field method (VFM) to a rectangular specimen loaded in the Iosipescu fixture. The displacement field over the gauge surface of the specimen is measured by the grid method. Two configurations are investigated: (1) with grain aligned along the specimen length (0° configuration) and (2) with grain at 45°. For the 0° configuration, only the parameters Q 11 and Q 66 are correctly identified, with coefficients of variation of the same order of magnitude as those obtained from reference tensile and shear tests. Better identification is obtained for the 45° configuration, for which only the parameter Q 12 exhibits large scatter. This improvement results from a more balanced influence of all stiffness parameters on the response of the 45° specimen. However, all stiffness parameters identified were systematically underestimated by approximately 30% in comparison to reference values. This deviation is due to the vertical spatial variation of the mechanical properties of wood within the stem. Literature data confirm this interpretation.
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August 8, 2007
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Common yew ( Taxus baccata L.) and Norway spruce ( Picea abies [L.] Karst.) are gymnosperm species that differ in their microscopic structure and mechanical characteristics. Compared to spruce, the density of yew wood is high, but the modulus of elasticity is low when loaded parallel to the grain. Information about the transverse load direction is largely lacking. Therefore, the goal of this study was to assess the elastic and fracture mechanical behaviour of both wood species in the radial-tangential plane (crack opening mode I). For this purpose, micro wedge splitting tests were performed. Characteristic elastic and fracture parameters (initial slope, critical load, specific fracture energy) were determined. After the tests, the fracture surfaces were evaluated using microscopic methods. The results reveal clear differences between the species regarding microscopic fracture phenomena and prove that yew wood was significantly stiffer than spruce wood. We suggest that the density and the cell geometry are predominantly responsible for both elasticity and failure behaviour in the transverse direction.
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August 8, 2007
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Young's modulus and shear modulus were simultaneously obtained in a three-point bending test based on Timoshenko's bending theory. Deflection curves of a bent beam were measured by image analysis, and the mechanical properties of the wood were calculated by polynomial regression analysis after excluding the singular region. When beam specimens of spruce ( Picea sp.) and mizunara ( Quercus crispula ) wood were tested, static Young's modulus ( E s ) and static shear modulus ( G s ) values could be obtained from the deflection curve using finite element analysis. By comparing the dynamic properties ( E d and G d ) obtained by a flexural vibration test, it was estimated that E s was greater than E d , while G s was less than G d . However, we suppose that the G s values calculated from the deflection curve are more plausible than those obtained from a conventional bending test.
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August 8, 2007
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Chamaecyparis formosensis is an endemic precious tree species grown in Taiwan. Based on the results obtained in our current study, the essential oil of C. formosensis wood possesses significant insecticidal activities. In an assay to assess mosquito larvicidal properties, the essential oil completely killed the larvae of Aedes aegypti and Aedes albopictus at a dosage of 100 μg ml -1 in water. Concentrations of the essential oil at a dosage of 0.16 mg cm -3 in air resulted in 100% mortality of silverfish after 2 h. It was found that the extractives of C. formosensis possess multiple bioactivities against insects. There is great potential for the development of insecticides for domestic application to kill mosquito larvae and silverfish based on this raw material.
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August 8, 2007
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There is wide variation in the extractive content and decay resistance of Scots pine ( Pinus sylvestris L.) heartwood. The heartwood is not visible in standing trees and only poorly visible in timber. Therefore, it is difficult to identify extractive-rich trees, and consequently the most decay-resistant heartwood. On the other hand, knots are clearly visible in standing trees and timber. In the present paper we studied the possibility of measuring the decay resistance of Scots pine heartwood indirectly on the basis of the extractive concentration of knotwood. The material investigated consisted of 40 felled trees with a wide between-tree variation for extractive content and decay resistance of their heartwood. The extractive content of knotwood was found to be four- to five-fold higher than that of heartwood. Statistically significant correlations were found between the mass loss of heartwood and the concentrations of total phenolics and stilbenes in knotwood (r=-0.54, P<0.001 and r=-0.40, P=0.011, respectively), and for the concentration of total phenolics (r=0.42, P=0.008) and stilbenes (r=0.39, P=0.012) between heartwood and knotwood. We suggest further development of this technique in the context of rapid industrial screening of durable pine heartwood.
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August 8, 2007
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A pulse-echo acoustic method was investigated for evaluating wood stake decomposition in the field. A total of 58 wood stakes (29 loblolly pine, Pinus taeda , and 29 aspen, Populus tremuloides ) that were vertically installed (full length) in forest soils were non-destructively tested by means of a laboratory-type acoustic measurement system. The same acoustic measurements were also conducted on the wood stakes after they were removed from the soil. Compression (parallel to grain) tests were then performed on the stakes in the laboratory to obtain residual elastic and strength properties. The results indicate that the pulse-echo acoustic method is a good approach to characterize wood stakes that are fully inserted into mineral soils. Statistical analysis showed good relationships between acoustic parameters (number of pulse echoes and in-ground acoustic velocity) and percentage weight loss, modulus of elasticity in compression, and residual compressive strength. The pulse-echo acoustic method could be used as a monitoring tool to assess progressive levels of wood stake decomposition in forest soil.
