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June 1, 2005
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Botryodiplodia theobromae is the predominant fungus causing sapstain in rubberwood in Kerala, India. The fungus causes up to 12.2 percent weight loss in rubberwood over a period of sixteen weeks. Transmission Electron Microscopy (TEM) of sapstained rubberwood provided evidence on hyphal invasion of cells by B. theobromae through the pit region, facilitated by its ability to degrade pit membranes. The study also revealed that B. theobromae caused degradation of lignified cell walls by erosion of the cell wall surfaces of wood elements.
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June 1, 2005
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The tolerance of various fungi against copper was examined. For this purpose, we impregnated Norway spruce ( Picea abies ) specimens with two different aqueous solutions: copper(II) octanoate with ethanolamine or copper(II) sulfate (c Cu = 1.0 × 10 −2 mol/l). Impregnated and unimpregnated test specimens were then exposed to brown rot fungi Antrodia vaillantii and Gloeophyllum trabeum or to white-rot fungi Schizophyllum commune and Trametes versicolor . After 2, 4, 6 and 12 weeks of exposure Electron Paramagnetic Resonance, Atomic Absorption Spectroscopy and mass loss measurements were performed. The results indicate that A. vaillantii, G. trabeum and T. versicolor transform copper(II) sulfate in wood into non-soluble, and therefore non-toxic, copper oxalate. The intensity of this reaction depends on the amount of excreted oxalic acid and was the highest for A. vaillantii and the lowest for T. versicolor . In the presence of ethanolamine, formation of insoluble copper oxalate was not possible and therefore, decay could not proceed. The major portion of copper remained in the wood and only minor amounts were in some cases translocated into nutrient media.
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June 1, 2005
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Eight transverse sections of hinoki ( Chamaecyparis obtusa Endl.) were analyzed along the grain near a knot by circularity index ( CI ), aspect ratio and equivalent diameter. The specimens were divided into two groups, one above and one below the knot, and their distances from the knot were 0 mm (the nearest), 12 mm, 24 mm, and 36 mm, respectively. Another sample was also selected from knot-free wood for reference along the same grain. A gradual decrease in the aspect ratio of tracheids demonstrated that both boundaries and lumina tended to have small differences in length and width as they approached the knot along the grain. CIs of lumina nearest to the knot indicated astonishingly high values with a narrow range from hexagon to ellipse, compared with the others ranging from rectangle, via hexagon, to ellipse. In other words, lumina showed a tendency to become round near the knot. In addition, the equivalent diameters of lumina tended to decrease when approaching the knot, implying that cell wall thickening of tracheids occur near the knot. It should be noted that the above variations in tracheids accompanied changes in grain orientation and annual ring width, especially the sharp transformation nearest to the knot.
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June 1, 2005
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Fibre length, microfibril angle and wood density were measured in eight-year-old Eucalyptus globulus clones planted on three different sites. Samples were chipped and pulped, and the pulps beaten prior to preparation of 60g/m 2 handsheets. Eleven physical handsheet properties, together with pulp freeness, were measured using standard methods. Direct relationships between wood properties and pulp/paper properties were studied using path analysis. Fibre length had a strong, direct effect on tear index, bending stiffness, freeness, pulp yield and active alkali consumption. Wood density was a strong predictor of most handsheet properties: high density woods produced bulkier, more porous sheets with higher bending stiffness, while lower density woods produced smoother, denser sheets with higher tensile strength.The effect of microfibril angle was small and more evident in handsheets made from beaten pulp.
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June 1, 2005
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June 1, 2005
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June 1, 2005
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The present paper establishes the relationship between certain components of oleoresin and the character of a tree as high producer (plus tree). The composition of the oleoresin (monoterpenes, sesquiterpenes, neutral diterpenes and resin acids) of Pinus pinaster in plus trees was studied by gaschromatography/mass spectrometry. The main components of the monoterpenes are α-pinene, β-pinene, limonene + β-phellandrene; of the sesquiterpenes β-caryophylene and longifolene; of neutral diterpenes isoabienol, abienol, isopimaral, pimaral, 11,13-labdien-8-ol and of resin acids levopimaric + palustric, neoabietic, abietic, isopimaric, pimaric, dehydroabietic, sandaracopimaric and 7,13,15 abietatrienoic acid. The components which enable us to distinguish between plus and control trees are myrcene and noracid 1 at a level of significance of 1%, and abienol and dehydroabietic acid at 5%. The composition of diterpenes permits a certain approach to distinguish between control and plus trees.
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June 1, 2005
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The phenolic content of condensed tannins varies considerably, depending on the method of determination. Even though the Stiasny precipitation number has been commonly used to estimate the amount of reactive tannin towards formaldehyde, particularly in adhesive applications, this estimation alone is not sufficient. In this study two methods of determining the amount of reactive tannin towards formaldehyde were examined. These were (1) the reactivity towards formaldehyde or the Stiasny precipitation number, and (2) the formaldehyde uptake. Five different types of tannin were examined from Rhizophora mucronata, P. radiata , mimosa, quebracho and chestnut. The study indicates that the phenolic content in tannin can be better estimated by determining both the Stiasny number and the amount of formaldehyde uptake. High correlation (r 2 = 0.905) was detected between the two methods. The study also revealed that hot water extracts of R. mucronata contain relatively small amounts of reactive polyphenols and are less reactive than sulfite extracts. The consumption of formaldehyde by this type of tannin was only 0.294 molecules per flavanoid unit. Similar to R. mucronata , the sulfite extracts of P. radiata contain relatively high amounts of reactive polyphenols and reacted with substantially higher amounts of formaldehyde per flavanoid unit, comparable to mimosa and quebracho tannins. Nonetheless, the reactivity towards formaldehyde (gel time) of the latter tannins is muchlower, despite their higher polyphenolic content. Of the two methods used to estimate the polyphenolic content of bark extracts, the Stiasny number had a relatively higher correlation (r 2 = 0.518) with gel time than formaldehyde uptake (r 2 = 0.345) did. The behaviour of these tannins in relation to their reactivity and chemical structures is discussed.
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June 1, 2005
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Cure behavior of resins formulated with petroleum phenol replaced by 25 and 50 wt% of softwood bark-derived pyrolysis oils, using various formaldehyde to phenolics molar ratios and alkalinity content, was characterized by Differential Scanning Calorimetry (DSC). Kinetic parameters were obtained by the Borchart-Daniels method and the model-free (Vyazovkin) method. Resins containing up to 50% by wt of pyrolysis oils had slower cure kinetics and lower extent of condensation reaction compared to a neat laboratory made phenol-formaldehyde resin. However, very similar kinetic curing behavior to the standard resins was found for resols having 25% by wt of the petroleum phenol replaced by the pyrolysis oils. Thermogravimetric analysis (TG) of cured pyrolysis oil-PF resins has been done under nitrogen and air environments at a constant heating rate. Thermal behavior of resins containing pyrolysis oils differed depending on the nature of the purge gas used in TG. Increasing the amount of pyrolysis oils decreased the thermal resistance of the experimental resins.
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June 1, 2005
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Phenol-formaldehyde (PF) resols were prepared with different proportions of phenol replaced with softwood bark pyrolysis oils under varying formaldehyde to phenolics molar ratios and sodium hydroxide contents. Propylene carbonate (PC) was added to these adhesives to improve the cure of resins. The cure behavior was characterized by differential scanning calorimetry (DSC). Cure kinetics and amount of cure of the experimental resin were improved by adding PC to the resins. Low amounts of PC were used (less than 1.5% of PC on a resin solid basis) to avoid premature gelling of the adhesives. Results obtained by DSC suggested that PC catalyzed the resin cure reaction and also participated in resin cross-linking reactions. Low percentages of PC, 0.5 and 1% on a resin solid basis, were added to the experimental resins for bonding strandboards. These addition levels did not significantly improve mechanical properties of strandboards. It is concluded that a PC addition level of more than 1% by wt (on a resin solid basis) should be used to modify the mechanical properties of panels bonded with pyrolysis oil-PF resins.
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June 1, 2005
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The steam explosion process was used to separate the components of aspen wood. The main goal was to obtain a material with a molecular weight distribution similar to that of dissolving pulp. To achieve variations in fibre structure and molecular weight, two series of steam explosions were made in which the time and temperature were varied according to factorial designs. The resulting pulps were very dark and were therefore bleached with hydrogen peroxide. The bleaching was sufficient to increase the brightness of the exploded material significantly. The resulting lignocellulosic materials as well as the washing water were characterised by carbohydrate analysis, lignin analysis and size-exclusion chromatography. A large variation in the pulp composition as well as in cellulose and hemicellulose molecular weight was obtained merely by varying the time and temperature of the explosions. The results showed that pulps with properties ranging from a high xylan content (7%) and high molecular weight cellulose (900 000) to a low xylose content (< 1%)and low molecular weight cellulose (<40 000) were produced. The exploded material consisted mainly of cellulose, hemicellulose and degraded polysaccharides. The degraded polysaccharides showed up as lignin in the Klason lignin analysis and in measurements of kappa number.
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June 1, 2005
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Reed canary grass ( Phalaris arundinacea L.) was delignified in a laboratory-scale digester by conventional soda-AQ pulping under varying conditions. The chemical composition of the corresponding black liquors was analyzed with respect to their main organic constituents. The results showed that the dry solids of the black liquors contained 33–34% lignin, 14–19% aliphatic carboxylic acids and 12–16% polysaccharides. No significant differences were found in the average molecular masses ( M̄ w 4700–5600 Da and M̄ n 650–750 Da) of the dissolved lignins in these black liquors, although the polydispersity ( M̄ w / M̄ n ) values (6.6–7.9) indicated that the molecular masses had a wide distribution. Lignin clearly degraded in the black liquors as delignification proceeded. Of the monosaccharide moieties detected in the polysaccharides, xylose was predominant, suggesting that xylan was a major hemicellulose constituent in the black liquors.
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June 1, 2005
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Loss of N from Sitka spruce timber was investigated by sampling battens before drying, after 5 and 41 days air drying, after exposure to a full kiln drying schedule and at 24 h intervals during kiln drying. Undried sapwood and heartwood had similar total N content. Kiln drying significantly reduced total N content of the sapwood and heartwood within the first 24 h of the drying schedule when wood temperature was below 50°C. Tests using timber from trees felled at different times of the year and grown in different locations with considerably different undried N content indicated a constant N loss of approx 30% of the total as a result of kiln drying. No evidence of absolute N enrichment of evaporation surfaces of battens was found, although a slight enrichment relative to wood within battens did develop as a result of kiln drying. Air drying also reduced N content but to a lesser extent than kiln drying, even after 41 days exposure. Nitrogen was lost more quickly from heartwood than sapwood during air drying. Loss of N from the wood appears to be in a gaseous or vapour form which is suggested to be through loss of naturally present ammonia and deamination of amino acids to produce further ammonia. GC-MS analysis of gasses/vapours released by wood samples indicated that molecules of 17 amu, which may include ammonia, were liberated in relatively large quantities from undried heartwood but not from partly kiln dried heartwood when heated. Sapwood released these molecules more slowly and continued to do so following partial kiln drying possibly indicating a less volatile source. Temperature gradients within battens during kiln drying were relatively small, with temperature similar to that of the kiln air.
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June 1, 2005
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The moisture content profile in the surface layer of Scots pine ( Pinus sylvestris ) sapwood has been measured using the MRI (Magnetic Resonance Imaging) technique.Anovel high-gradient permanent magnet was used for the measurement of the moisture profile in the wood during the drying process, giving a depth resolution of better than 20 μm. This paper demonstrates for the first time the possibility of measuring the moisture content depth profile in the surface layer from raw state down to 4% moisture content without removing the wood sample from the apparatus. The main advantage of this technique and apparatus is a high resolution over a large field of view. It is possible to measure the moisture content in the wood surface layer during drying up to a depth of 300 μm. A single moisture content profile may be obtained in less than 5 min. Hence, more accurate dynamic drying information, on a single sample, maybe achieved than with current techniques. In this preliminary studywe observed that the wood cells at the surface had a moisture content higher than the equilibrium moisture content for wood in the surrounding bulk air. We conclude that for a wood moisture content of above approximately 50% the resulting profiles were almost flat from a depth of 90 μm and further into the wood and in between the surface and 90 μm deep there was a steep gradient. Below 50% there was a gradient in moisture content to at least 300 μm depth.
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June 1, 2005
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To create a model of beech wood drying in the hygroscopic range, knowledge of longitudinal permeability and diffusivity parameters of wet air in wood is needed. These data were obtained using a Wicke-Kallenbach-cell running in an open system and crossed either by an inert gas (nitrogen) or by two streams of two inert gases (helium and nitrogen), that prevent the adsorption phenomena in wood. Taking into account the relations between apparent and molecular diffusivities, the diffusivities of steam could be calculated from those of helium. Longitudinal diffusivity and permeability increase slightly with the moisture content of wood; the average values obtained at the ambient temperature (20°C) for the axial diffusivity (8. 1. 10 −6 m 2 /s) and for the axial permeability (2. 2. 10 −11 m 2 ) are compatible with those reported in the literature for this species.
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June 1, 2005
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Kinetic evidence from thermomechanical analysis experiments and 13 C NMR evidence were used to show that the strength of a joint bonded with UF/pMDI glue-mixtures is improved by coreaction between pMDI and UF resin methylol groups forming methylene cross-links. These are predominant, as opposed to the formation of urethane bridges which still appear to form, but are in great minority. The coreaction occurs in the presence of water and under the predominantly acidic hardening conditions characteristic of aminoplastic resins (in presence of a hardener). Coreaction occurs to a much lesser extent under alkaline conditions (without UF resins hardeners). The predominant reaction is therefore different in UF/pMDI and PF/pMDI adhesive systems. The same reaction observed for the UF/pMDI system at higher temperatures was also observed in PF/pMDI systems, but only at lower temperatures. The water introduced into the UF/pMDI mixture by addition of the UF resin solution was shown not to react with pMDI to increase the strength of the hardened adhesive to a significant degree.
