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June 1, 2005
Abstract
Anionic effects are demonstrated with Mg-salts and free acids in high alcohol content organosolv pulping. Not all catalysts examined could effectively liberate the fibers from the wood matrix. The best result was obtained with the 0.025 M MgCl 2 catalysis system, at which nearly 60% screened pulp, with viscosity of 19.9 cPs., can be produced. Mg(NO 3 ) 2 was found capable of liberating fibers, however, under the conditions set for the experiment, complete fiber liberation was not achieved. In contrast, MgSO 4 and Mg(CH 3 COO) 2 were incapable of fiber liberation in themselves. On the other hand, in acid form, HCl and H 2 SO 4 were capable of liberating the fibers, whereas HNO 3 and CH 3 COOH catalysts were found ineffective. Especially with H 2 SO 4 , it should be noted that this catalysis system created a very strong hydrolyzing effect that unselectively destroyed both lignin and carbohydrates, resulting in severely damaged pulp which is useless for papermaking purposes. Therefore, choosing a suitable catalyst is the key factor for producing an organosolv pulp at high yield and with good fiber quality.
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June 1, 2005
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Catalyst employment in cooking liquor of 80% aqueous methanol is required for fiber liberation at high yield (50%) and has a remarkable impact on pulp production capability in the alcohol organosolv pulping of spruce wood. In alcohol solution without a suitable catalyst, the softwood fibers cannot be effectively liberated from the wood matrix. The effectiveness of the catalysts tested in this research varied widely. Divalent metal ions were found to be very effective, whereas monovalent cations were incapable of fiber liberation and trivalent cations were found to be too aggressive and hydrolyzed the carbohydrates, causing extensive damage to the fibers. Under the specified pulping conditions, the divalent metal ion catalyzed alcohol organosolv pulping process was capable of producing 60–61% screened pulp. Successful chemical pulp production by the NAEM (Neutral Alkali Earth Metal) catalyzed organosolv pulping process opens access to biorefining and provides value recovery both from the pulp and also from the dissolved wood components from the spent pulping liquor.
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June 1, 2005
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The present study investigated different log storage conditions and their influence on the processability of the wood material in pulping and bleaching. For that purpose, logs were stored for about 15 months under dry and wet conditions. Besides a detailed chemical, physical and microbial characterization of the wood, cooking trials according to the standard magnesium acid bisulfite process and bleaching experiments at various conditions using a (E/O)-Z-P-sequence were performed. The dependency of pulp yield, delignification efficiency, the course of cellulose depolymerization and brightness on the different storage conditions was evaluated. Bleaching selectivity was comparable for pulps made from fresh and wet-stored wood. In the case of pulp made from dry-stored wood, between 60% and 300% more bleaching chemicals, expressed as OXE, were necessary to obtain the target brightness. Milled wood lignin was isolated from the beech wood samples to study possible structural changes attributable to different storage conditions. Permanganate oxidation was applied to investigate the most important lignin structures. Additionally, preliminary NMR studies were performed to gain supplementary information about the composition of the lignin moieties. UV microspectrophotometry in agreement with absorption difference spectra strongly suggests that the chromophore structures present in both unbleached and bleached pulp samples predominantly originate from polyphenolic compounds, which are attached to the cell wall and are deposited in the lumina of parenchyma cells. From the results obtained so far, it can be concluded that wet storage of beech wood logs efficiently prevents the formation of chromophore compounds which negatively affect acid bisulfite pulping.
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June 1, 2005
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The surface inactivation of two wood species, yellow poplar ( Liriodendron tulipifera ) and southern pine ( Pinus taeda ), was studied following high temperature drying. Surface analysis involved X-ray photoelectron spectroscopy, sessile drop wettability and fracture mechanics of the adhesively-jointed surfaces. The results showed that wood drying at high temperature (i.e., >160 to 180 °C) caused modifications in surface composition. The oxygen to carbon ratio (O/C) decreased and the ratio of carbon atoms bonded to other carbon or to hydrogen atoms vis-à-vis carbons bonded to oxygen atoms (i.e., the C1/C2 ratio) increased with drying temperature. In addition, the contact angle increased with the temperature of exposure, but decreased with time. A dependence on wood species was evident: southern pine surfaces always exhibited higher contact angles than yellow poplar. Also, the rate of contact angle decline with time, dθ/dt, was found to vary with surface composition: this rate corresponded to O/C ratio-changes, especially in the case of southern pine. Southern pine was most susceptible to inactivation particularly when bonded with PF adhesive. Yellow poplar surfaces did not show significant inactivation when exposed to drying temperatures below ca . 180 °C. The results are explained by a relative enrichment of wood surfaces with non-polar substances, hydrophobic extractives and volatile organic compounds that 'become visually evident during the drying process at temperatures above ca. 160 °C. Little change was observed if drying temperatures remained below 150 °C.
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June 1, 2005
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Moisture adsorption isotherms were determined for untreated and copper-ethanolamine (Cu-EA) treated wood at different copper retention levels. The Cu-EA treatment reduces the water vapor accessibility in wood because copper has occupied some of the adsorption sites for moisture during the treatment. The percentage of adsorption sites occupied by copper was evaluated by M t / M u , which is the ratio of equilibrium moisture content for treated wood to untreated wood. The results show that, within the copper retention range used in this study, the M t / M u value decreases linearly at lower temperatures (4 and 15 °C) or logarithmically at higher temperatures (30 and 40 °C) with the increase of copper retention, suggesting that the percentage of adsorption sites occupied by copper ( P ) increases linearly or logarithmically with the copper retention in Cu-EA treated wood. P decreases with the increase of relative humidity. The reason is that more adsorption sites become available for moisture at higher relative humidity. It has also been found that the influence of Cu-EA treatment on hydrated water ( M h ) is more significant than that on dissolved water ( M s ).
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June 1, 2005
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The exceptional natural durability of Prosopis africana heartwood was investigated to find potential new biocides for wood preservation. Extractions carried out with different solvents indicated high levels of extractives which explained wood durability towards fungal and insects attacks. However, the extractives were not enough to explain the durability. The hydrophobic character of the wood also likely had a significant effect. Contact angle measurements before and after extraction, indicated that extractives have only a minor effect on wood hydrophobicity. Microscopic analysis reveals the presence of high levels of gums filling the wood cell lumens, limiting the penetration of water.
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June 1, 2005
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Mechanically-induced wood flow welding, without any adhesive, is here shown to rapidly yield wood joints satisfying the relevant requirements for structural application. The mechanism of mechanically-induced vibrational wood flow welding is shown to be due mostly to the melting and flowing of the amorphous polymer materials interconnecting wood cells, mainly lignin, but also some hemicelluloses. This causes the partial detachment of long wood cells and wood fibres and the formation of an entanglement network in a matrix of melted material which then solidifies. Thus, it forms a wood cell/fibre entanglement network composite having a molten lignin polymer matrix. During the welding period, some of the detached wood fibres no longer held by the interconnecting material are pushed out of the joint as excess fibre. Cross-linking chemical reactions of lignin and of carbohydrate-derived furfural also occur. Their presence has been identified by CP-MAS 13 C NMR. These reactions are, however, relatively minor contributors during the very short welding period. Their contribution increases after welding has finished, explaining why relatively longer holding times under pressure after the end of welding contribute strongly to obtaining a good bond.
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June 1, 2005
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The effect of growth site type, felling season, storage time and kiln drying on the contents and distributions of phenolic extractives and low molar mass carbohydrates in secondary xylem of silver birch Betula pendula was studied. The results indicated that the total amount of methanol-soluble extractives did not change markedly under the prevailing conditions of the study. However, the contents of phenolic compounds, (+)-catechin and (+)-catechin-7-O-β-D-xylopyranoside, and low molar mass sugars, D(+)-xylose, D(−)-fructose, D(+)-glucose, sucrose, maltose and raffinose, changed with season, storage time, radial location in the stem or growth site type. The glycosidic bond in (+)-catechin-7-O-β-D-xylopyranoside, sucrose, maltose and raffinose was hydrolysed with kiln drying, resulting in elevated contents of the monosaccharides, D(+)-xylose, D(−)-fructose, D(+)-glucose, in kiln dried boards. Surprisingly, the content of (+)-catechin did not increase simultaneously with the breakdown of (+)-catechin-7-O-β-D-xylopyranoside, indicating that (+)-catechin may polymerise or have another bonding pattern with other wood components due to elevated temperatures during kiln drying. In addition, the relative amount of phenolic compounds, (+)-catechin monomer and its glycoside, (+)-catechin-7-O-β-D-xylopyranoside, in the methanol extracts decreased with partial vacuum drying.
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June 1, 2005
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Eight Pinus radiata D. Don increment core samples were selected from a total of 32 cores for the development of calibrations for several tracheid morphological characteristics: coarseness, perimeter, radial and tangential diameter and wall thickness. Near infrared (NIR) spectra, obtained from the radial-longitudinal face of each core in 10-mm sections from pith to bark, were used to develop the calibrations. Calibrations for coarseness and wall thickness were excellent, with coefficients of determination (R 2 ) of 0.91 and 0.89, respectively. Calibrations for the remaining characteristics were weaker (R 2 ranged from 0.65 to 0.69). To test the predictive ability of the calibrations, two intact P. radiata increment cores (core A and B) were selected from the same set as the calibration samples. NIR-predicted tracheid coarseness and wall thickness were in strong agreement with measured (SilviScan-determined) values. Radial patterns of variation (NIR-predicted, measured) closely followed each other for both cores, but coarseness and wall thickness were underestimated for core B. Tracheid tangential perimeter was well predicted with R 2 of 0.69 (core A) and 0.79 (core B). Relationships for the remaining characteristics were weak. Collection of NIR spectra in smaller increments, to capture more of the variation, may improve calibration.
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June 1, 2005
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The reddish-violet heartwood of Juniperus virginiana L. contains irregularly distributed and longitudinally oriented streaks of light-coloured wood, described as “included sapwood”. A histological study revealed that a blockage of the rays, which is caused by wounds often associated with tiny shakes, branch stubs and included bark, may lead to this anomaly. A study of fresh wood immediately after felling of the trees showed that “included sapwood” lacks physiological activity similar to the adjacent normal heartwood. Cellular UV-spectroscopic analysis revealed a secondary metabolism particularly of phenolic compounds in the pit membranes of tracheids during “included sapwood” formation, whereas the reddish-violet flavonoid compounds do not develop in this anomalous wood. Chemical analyses of petrol ether, diethyl ether, acetone and ethanol/water extracts of sapwood, “included sapwood” and heartwood showed that the accessory compounds cedrol, α-cedrene, widdrol, thujopsene and cuparene increased in “included sapwood” compared to sapwood. As opposed to the reddish-violet heartwood compounds, these sesquiterpenes turned out to be highly toxic against a brown-rot fungus in a bioassay. These findings justify defining “included sapwood” as a heartwood anomaly, since the important wood characteristics of this tissue obey the definition of heartwood rather than sapwood. This anomaly should no longer be a reason to exclude this type of wood from commercial utilisation.
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June 1, 2005
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Raman spectroscopy using 400 nm excitation was successfully applied to chemical pulp samples and the fluorescence background that usually limits the application of this method to such samples was effectively suppressed. This enabled the detection of much weaker Raman bands from the pulps. The rejection ratio of the fluorescence background to Raman scattering was estimated to be about 250. The resonance Raman spectra of peroxide bleached chemical pulps had chromophoric lignin bands at 1605 and 1655 cm −1 , whereas the chlorine dioxide bleached pulps had only the aromatic band at 1605 cm −1 . The square root of the aromatic chromophore band relative to cellulose band correlated linearly with the brightness which is in accordance with the Kubelka-Munk theory. This correlation indicated that the resonance enhanced Raman bands were mainly due to chromophoric lignin structures. Chlorine dioxide and peroxide bleached pulps gave different correlations to brightness, which was an indication of different kinds of chromophores in these pulps. The intensity of the aromatic band relative to the cellulose band was about 20 times higher with the ultraviolet (257 nm) than with the visible (400 nm) excitation. This clearly illustrated the importance of working with different excitation wavelengths. On one hand the UV excitation is more sensitive towards aromatic residual lignin in pulp, and on the other hand the visible excitation enables the selective detection of chromophoric lignin structures.
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June 1, 2005
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Wood was sampled from 22 locations in 3 Pinus radiata trees and characterized by solid-state 13 C NMR spectroscopy. Values of a cellulose crystallinity index were confined to the range 0.486 to 0.541 despite inclusion of earlywood and latewood, compression wood and opposite wood, juvenile wood and mature wood. The mean value was 0.515 and the standard deviation was 0.015. Highest crystallinity was associated with relatively slow radial growth, with a correlation coefficient of R =−0.79 for a linear least-squares fit against ring width. The NMR results were consistent with published studies based on X-ray peak widths. Crystallinity indices based on X-ray peak heights or areas have shown wider ranges of variation, attributed to differences in cellulose content rather than cellulose crystallinity.
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June 1, 2005
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Four methyl cellulose samples in the degree of substitution range from 0.5 to 2.0 were characterised by combination of different analytical methods. Samples were analysed regarding their partial degree of substitution by hydrolysis and anion exchange chromatography with pulsed amperometric detection. For calibration of the chromatographic system, standard substances were isolated by preparative HPLC and their structure was confirmed by 13 C-NMR spectroscopy. For two methyl cellulose samples per-acetylation and 13 C-NMR with inverse gated decoupling was carried out for comparison with the chromatographic analysis. Endoglucanase fragmentation of methyl celluloses was performed and water-soluble and insoluble fractions were analysed separately. A preparative size exclusion chromatography system for enzymatic-degraded water-soluble methyl cellulose was developed and the molar masses of the individual fractions were examined by analytical size exclusion chromatography. By combination of endoglucanase fragmentation, preparative chromatography, hydrolysis and anion exchange chromatography an approach for the analysis of the substitutent distribution along the polymeric chain of water-soluble methyl cellulose could be established.
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June 1, 2005
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July 27, 2005
