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June 1, 2005
Abstract
Delignification with the use of monoethanolamine (MEA) is an innovative, environmentally friendly chemical pulping process that, in contrast to conventional pulping methods, works without the use of sulphur compounds. Of particular benefit is the simple MEA recovery by distillation, allowing black liquor combustion to be dispensed with and the dissolved lignin to be gained. The MEA process is suitable for pulping both hardwood (e.g. beech) and softwood (e.g. spruce). Compared with conventional processes, the MEA process has the advantage of achieving a high degree of delignification through an increase in temperature during pulping without any appreciable damage to the cellulose. When manufacturing dissolving pulps, however, this specific selectivity of MEA requires the removal of the hemicelluloses in an additional stage, preferably by acid prehydrolysis. The conditions of this prehydrolysis step must be selected specifically to be in keeping with the ultimate use of the dissolving pulp, as this stage involves the cellulose chains being chemically attacked. The residual lignin is removed after pulping in a sequence of different bleaching stages. Substituting MEA for the sodium hydroxide solution required as a bleaching alkali in the oxygen delignification stage proves to be especially beneficial, as in this case the COD after bleaching can be considerably reduced by treating the bleaching filtrate from this stage jointly with the effluents from the MEA pulping process.
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June 1, 2005
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Kraft and oxygen delignified pulps with various kappa numbers were prepared from black spruce and western hemlock chips. The bleachability (ratio of kappa number decrease to chlorine dioxide applied) of the different pulps at the same kappa number varied with both wood furnish and delignification process. Thus, unbleached kappa number alone is not a reliable indicator of bleachability for these pulps. This may be due in part to the variable hexenuronic acid content of the pulps; those with higher ratio of hexenuronic acid content to kappa number (HexA/kappa) are harder to bleach. Voltammetric analysis of the same kraft pulps in the presence of redox mediators was found to measure both the content and reactivity of residual lignin. Peak current ratios of redox mediators correlated with pulp bleachability for all pulps. These ratios may therefore provide a more accurate prediction of bleachability than unbleached kappa number.
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June 1, 2005
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To address the chemical behavior of beech xylan ( O -acetyl-4- O -methyl-glucuronoxylan) under alkaline conditions, three model compounds, 2- O -methylxylobiose ( 1 ), aldobiouronic acid (4- O -methyl-α-D-glucopyranosyluronic acid-(1→2)-xylose, 2 ), and aldotriouronic acid (4- O methyl-α-D-glucopyranosyluronic acid-(1→2)-β-D-xylopyranosyl-(1→4)-D-xylose, 3 ), were subjected to strong alkaline conditions equal to those used for the industrial production of viscose (18% NaOH, 43°C). Kinetics of the degradation of the model compounds were monitored by capillary electrophoresis in combination with pre-column derivatization. It was demonstrated that substitution at O-2 of the reducing xylose unit strongly retarded the alkaline degradation reactions ( 1 and 2 ). By isotopic labeling experiments and isolation of degradation products it was shown that under the pertinent conditions deprotonation at C-2 occurs, followed by epimerization to the respective lyxo derivative. Aldotriouronic acid 3 was degraded to 2 as an intermediate according to classical peeling pathways. Genuine degradation reactions and epimerization processes were distinguished.
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June 1, 2005
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The effect of UV irradiation on unbleached and TCF-bleached dissolving pulp samples of different provenience, a beech sulphite and an eucalyptus prehydrolysis kraft pulp, has been analyzed according to the CCOA method, evaluating the changes in the molecular weight distribution, the total number of carbonyl groups and the carbonyl group profiles of each pulp. In the case of TCF bleached material, slightly more carbonyl groups were introduced into the kraft pulp as compared to the sulfite pulp. Cellulose degradation was relatively low in both pulps. In the case of unbleached sulfite pulps, the residual lignin had only a minor effect on the molecular weight distribution and the oxidation state of the cellulose, whereas for eucalyptus kraft pulp a pronounced introduction of carbonyl groups accompanied by severe degradation of cellulose was observed. The presence of hemicelluloses governed the photochemical behavior and the carbonyl profiles of the low molecular weight region of the cellulose.
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June 1, 2005
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Three kraft pulps in the kappa number range between 50 and 20 and the same pulps oxygen-delignified to similar lignin contents (kappa approximately 6) were analyzed for lignin-carbohydrate complexes (LCC) by a method based on selective enzymatic hydrolysis of the cellulose, and quantitative fractionation of the LCC. Between 85 and 90% of residual lignin in the unbleached kraft pulp and all residual lignin in the oxygen-delignified pulps were isolated as LCC. Three types of complexes were found; viz., xylan-lignin, glucomannan-lignin-xylan and glucanlignin complexes. After pulping to a high kappa number, most of the residual lignin was linked to xylan. Different delignification rates were observed so that most of the residual lignin was linked to glucomannan when the pulping was extended to a low kappa number. With increasing degree of oxygen delignification, a similar trend in the delignification rates of LCC was observed so that the residual lignin was increasingly linked to glucomannan. Complex LCC network structures seemed to be degraded into simpler structures during delignification. The differences in delignification rates are discussed with reference to the solubility properties and structural differences of LCC, and to morphological aspects of the pulp.
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June 1, 2005
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Residual lignin carbohydrate complexes (RLCC) were isolated enzymatically from spruce and pine pulp. The RLCCs contained 4.9–9.4% carbohydrates, with an enrichment of galactose and arabinose compared to the original pulp samples. The main carbohydrate units present in all studied RLCCs were 4-substituted xylose, 4-, 3- and 3,6-substituted galactose, 4-substituted glucose and 4 and 4,6-substituted mannose. These units were assigned to carbohydrate residues of xylan, 1,4- and 1,3/6-linked galactan, cellulose and glucomannan. RLCCs of surface material and the inner part of spruce kraft pulp fiber were compared to obtain information on the heterogeneity of layers of the fiber wall. The 1,4-linked galactan was the major galactan in RLCC of fiber surface material of spruce kraft pulp. Towards the inner part of the fiber, the proportion of 1,3/6-linked galactan increased relative to 1,4-linked galactan. This finding is presented for the first time. 1,3/6-Linked galactan structures are suggested to have a role in restricting lignin removal from the secondary fiber wall. RLCCs of three different alkaline pine pulps were studied before and after oxygen delignification to evaluate differences resulting from the cooking method. The pulps were conventional kraft pine pulp (PCK), a polysulfide/anthraquinone pine pulp (PPSAQ) and a soda/anthraquinone pine pulp (PSoAQ); all were cooked to approximately kappa number 30. Small differences were found in the carbohydrate structures of the unbleached pulps. The study indicated that the RLCC of unbleached PSoAQ pulp contained longer oligomeric carbohydrate chains and less branched 1,3/6-linked galactan residues than the RLCCs of unbleached PCK and PPSAQ pulps. The RLCC of the unbleached PSoAQ also contained more 1,4-linked glucose units suggesting a greater number of linkages of lignin to cellulose in the PSoAQ pulp than in the other two pulps. All RLCCs of oxygen-delignified pulps had more non-reducing ends and less 1,3/6-linked galactan than the corresponding RLCCs of the unbleached pulps. The RLCC of the oxygen-delignified PSoAQ pulp had a higher ratio of 1,4-galactan to 1,3/6-linked galactan and shorter xylan residues than the RLCCs of oxygen-delignified PCK and PPSAQ pulps.
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June 1, 2005
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Pine kraft lignin was purified to obtain a kraft lignin preparation (KL) with weight average molecular mass (M w ) of 5500. The KL was then ozonated with an ozone-air stream containing 2–2.5% of ozone in 0.1 M sodium hydroxide solution to prepare ozonated kraft lignin preparations with ozone consumption of 10, 25, 30 and 40% per KL; Oz-10-KL, Oz-25-KL, Oz-30-KL and Oz-40-KL, respectively. The pH of reaction mixture was decreased with increasing ozone consumption, while the carboxylic acid content and the M w of resulting ozonated lignins increase with increasing ozone consumption. The KL and its ozonated preparations were then characterized by elemental composition, functional group analysis, molecular mass distribution and nitrobenzene-K 4 MnO 4 oxidation. The results showed that the KL extensively undergoes oxidative cleavage of both side chains and aromatic moieties without decrease in the M w as well as dehydrogenationive coupling of phenolic degraded fragments by active oxygen radical species, such as hydroperoxyl and hydroxyl radicals. The formation of these active oxygen radical species are produced by way of a series of reactions initiated by the reaction of ozone with hydroxide anions at pH range of 12.4–10.5, producing superoxide ( - O 2 •) and hydroperoxyl (HOO•) radicals.
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June 1, 2005
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The surface tension and interfacial tension of the F-1000, F-1800, F-5000 and F-15000 fractions obtained by ultrafiltration of the Oz-25-KL, Oz-30-KL and Oz-40-KL preparations (ozonated kraft lignin, KL, preparations with ozone consumption of 25, 30 and 40% per KL) were determined with the concentration range of 1–30 g l -1 at pH of 6, 9 and 11. The surface tension of these ozonated KL preparations decreased with increasing concentration and pH according to the simplified Gibbs adsorption equation for dilute aqueous solution, ∂γ= - RT Γ∂(ln C). The results were discussed in term of functional group contents and weight average molecular mass (M w ) of the ozonated KL preparations. The surface tension of the ozonated KL preparations decreased with increasing carboxylic acid content and, to some extent, phenolic hydroxyl content, but increased with increasing M w . The synergistic effect of the ozonated KL preparations with a commercial surfactant was then investigated. The oil-water interfacial tension was determined in the ozonated KL preparations in an aqueous solution containing 1.5% Petrostep B-120 R and 1.5% sodium chloride with hexane as oil phase by spinning drop technique. The interfacial tension of the system also decreased with increasing the concentration of ozonated KL preparations in the range of 1–16 g l -1 according to the simplified Gibbs adsorption equation. Thus, the addition of a small amount of ozonated KL preparations to the aqueous solution containing 1.5% Petrostep B-120 R and 1.5% sodium chloride showed a remarkable synergistic effect on reducing the interfacial tension.
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June 1, 2005
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The lignin oxidation in the oxygen delignification/bleaching process catalysed by Mn(II) substituted heptamolybdopentavanadophosphate polyanion (HPA-5-Mn II ) was studied using monomeric lignin model compounds and Eucalyptus globulus dioxane lignin adsorbed on the bleached sulphite pulp. The analysis of reaction products after lignin models oxidation in the presence HPA-5-Mn II and the parent heptamolybdopentavanadophosphate polyanion (HPA-5) showed similar qualitative and quantitative patterns, indicating the identical lignin oxidative delignification mechanisms with both catalysts. The higher delignification selectivity of the pulp in the reaction system HPA-5-Mn II /O 2 than with HPA-5/O 2 was explained by the protective effect of Mn II in the heteropolyanion towards oxidative degradation of polysaccharides. The study of lignin adsorbed on bleached sulphite pulp, in the HPA-5-Mn II /O 2 delignification system, showed the cleavage of β- O -4 linkages as the major contribution to the lignin depolymerisation. The formation of Cα- O -polysaccharide linkages in β- O -4 structures of lignin during the delignification was observed.
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June 1, 2005
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Knots, i.e. branch bases inside tree stems, in fir trees contained remarkably higher concentrations of lignans, oligolignans, and juvabiones than the adjacent stemwood. Eight fir species were analysed ( Abies sibirica , A. lasiocarpa , A. balsamea , A. alba , A. amabilis , A. veitchii , A. sachalinensis , and A. concolor ). The amount of lignans could in some knots exceeds 6% (w/w) and the knots generally contained 20–50 times more lignans than the stemwood. However, there were large variations, not only between species but also even between knots in the same tree. Secoisolariciresinol was the predominant lignan in all knots. The lignans occur in free form in the knots and are easily extracted with polar solvents. In addition to the lignans, oligomeric aromatic substances, mainly sesquineo- and dineolignans, and juvabiones were accumulated in the knotwood. Secoisolariciresinol, but also lariciresinol ( Abies alba ) and 7-hydroxymatairesinol ( A. amabilis ), could be extracted in large scale from fir knots at pulp and paper mills. The ready availability of large amounts of lignans and oligolignans now enables research to assess their bioactivity and provide the base for applications in medicine and nutrition, or as natural antioxidants and antimicrobial agents in various technical products.
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June 1, 2005
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The subject of study is the emission of Volatile Organic Compounds (VOC) during the drying of wood. Heartwood and sapwood from Scots pine were dried at different temperatures (50, 70 and 90°C) in a laboratory kiln. The sampling method, Solid Phase Microextraction was used to collect the different volatile organic compounds during the drying. The gas chromatograph and mass spectrometer was used to identify and quantify the organic matter. The total hydrocarbons were measured with a flame ionization detector. Primarily, different monoterpenes were released during the drying process. 3-carene and α-pinene were most common and were also analytically quantified. The diterpene, pimaral, was found in an estimated large amount in the later stage of the drying process but was not exactly quantified. Large differences in both release behavior and total amount of released hydrocarbon between heart- and sapwood were obtained. Emissions of VOC from heartwood were of a magnitude approximately three times higher than that from sapwood.
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June 1, 2005
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The effect of cyclic tension-torsion combined loading on the fatigue behavior and stress-strain properties of wood (Japanese cypress) was investigated experimentally. The specimen used in the experiments was a rectangular bar with its major axis in the fiber (longitudinal) direction of wood. Pulsating tension and torsion loadings were respectively applied along and around the longitudinal axis of the specimen. According to the relationships between stress and strain obtained using fatigue tests, the secant modulus of the stress-strain curve changed with an increase in the number of loading cycles, and the differences between the curves for tension and shear were observed. The obtained results of fatigue tests were found to be influenced by the combined stress ratios and the applied stress levels. Bordering on the combined stress state of TB, where tensile and shear stress components were almost equally applied, the trend toward lower stiffness retention was different between tension and shear, and the tensile or torsion failure mode became dominant in the failure mode. The TB state was recognized as a boundary state for both of the stiffness retention and the failure mode. The stiffness retention in the TB state showed a tendency similar to that in the stress state where torsion was dominant regardless of the stress level. On the other hand, the failure mode tended to be tension failure at higher stress levels. Thus, at higher stress levels in the TB state, the effect of the tensile or shear stress component on the fatigue behavior of wood was different between “during the fatigue process” and “the time of failure”. In addition, torsion was dominant for both during the fatigue process and the time of failure at lower stress levels.
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June 1, 2005
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The roles of density and microfibril angle in causing low stiffness in radiata pine butt logs were studied in detail on a 17-year-old tree. Distributions of these variables were compared with stiffness variations in the vertical direction. Results supported the hypothesis that cell ultrastructure is responsible for the vertical variation in stiffness. The microfibril orientation in tangential wall is considered to be an important factor contributing to wood stiffness because of the smaller microfibril angles compared with radial microfibril angles, and also because of the larger decrease of the microfibril angles with the rapid increase of wood stiffness in vertical direction especially in corewood zone. The microfibrils in the S3 layer fall from over 80° to angles of 54° and 51° for radial and tangential cell walls at the top of the butt log. Further study is needed for fully understanding the characteristics of S3 layers.
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June 1, 2005
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Two brown-rot wood decay fungi, Fomitopsis pinicola and Meruliporia incrassata , and the white-rot species Phanerochaete chrysosporium were grown for 4 weeks in liquid culture at 0.35, 0.70, 1.05, and 5.00 mM calcium (Ca) and 1.35 and 2.70 mM magnesium (Mg) concentrations. Soluble and total oxalate levels were quantified using a revised ion-exchange HPLC protocol developed specifically for resolving oxalate and other organic acid anions from medium components. Total oxalate concentrations in brown-rot filtrate were not significantly different among treatments; however, soluble oxalate decreased significantly with increasing Ca concentration. Higher Mg concentrations increased soluble oxalate levels only slightly. There was a significant decrease in medium pH at 5.00 mM Ca for all species, as well as an apparent increase in decarboxylation activity in brown-rot fungi. Total and soluble oxalate levels in the white-rot cultures were generally below detection for all treatments. The results show a significant influence of Ca on soluble oxalate concentrations not seen previously in the brown-rot species Postia placenta .
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