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February 1, 2005
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June 1, 2005
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The affect of phenolic hydroxyl groups on the reaction efficiency during chlorine dioxide pre-bleaching of a softwood kraft pulp was investigated. The removal of phenolic hydroxyl groups via pulp methylation did not adversely affect the chlorine dioxide bleaching efficiency or the amount of chlorate formed during exposure to chlorine dioxide. Ion analysis of the reaction systems revealed that the formation of chloride and chlorite ions during the bleaching process were very similar between the kraft and methylated kraft pulps. These results indicate that the kinetic rates of lignin oxidation by chlorine dioxide and its reduction products, chlorite and hypochlorous acid, are much faster than the rate of inorganic reactions leading to chlorate formation.
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June 1, 2005
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Lignins from kraft and mechanical pulps were isolated before and after oxygen treatment with conventional methods (acidolysis and enzymatic isolation) and with a novel two-step method combining an enzymatic treatment and acidolysis. Results showed that the combined enzymatic hydrolysis-acidolysis made it possible to extract lignin from pulp with a better yield than acidolysis alone and with a higher degree of purity than after enzymatic hydrolysis alone. The lignin samples isolated with the two-step method were analysed by 13 C NMR, 19 F NMR and by gel permeation chromatography. It was shown that the behaviour of mechanical pulp lignin during oxygen treatment was different from that of kraft pulp lignin. Most of these differences could be explained by the lower phenolic content and larger molecular size of the mechanical pulp lignin. As a consequence, oxygen had a poor delignifying effect. Finally, 19 F NMR spectroscopy showed that oxygen could destroy some quinones induced by the alkaline conditions of the O stage.
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June 1, 2005
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A novel analytical protocol for the absolute determination of the various polysulfide species present in alkaline aqueous media was developed. The method is comprised of alkylating polysulfide ions with dimethyl sulfate, followed by quantitative proton NMR spectroscopy using 1,3,5-tributyl benzene as the internal standard. In order to arrive at a quantitative acquisition protocol, a number of variables were examined in detail for their effect on the alkylation reaction, including the presence of oxygen, the amount of dimethyl sulfate and sodium hydroxide, and the various modes of adding the alkylating reagent to the reaction mixture. Most of these variables were found to play a role in determining the quantitative reliability of the procedure. Consequently, a method is described that can be used for the efficient and reliable quantitative detection of polysulfide ions. The protocol developed could be particularly useful in promoting our understanding of the intricate and delicate chemistry of polysulfide equilibria in aqueous alkaline media.
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June 1, 2005
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Carbonate (CO 3 •− ) and hydroxyl (HO • ) radicals were chemically produced in cotton linter suspensions using peroxynitrite as a radical precursor. Both radicals could degrade cotton linters, as shown by viscosity and GPC-SEC measurements. As evidenced by the viscosity measurements, the presence of oxygen during the cotton linter treatments slightly increased cellulose degradation by both radicals. For the carbonate radical, more than 90% of the viscosity losses could be recovered by reductive NaBH 4 treatment before measuring the viscosity, whereas only approximately 40% of the viscosity was recovered after hydroxyl radical degradation and subsequent NaBH 4 treatment. This indicates that carbonate radicals mainly abstract H-atoms adjacent to hydroxyl groups, i.e., at C 2 , C 3 and C 6 . This intramolecular selectivity may reflect a polar effect, whereby hydrogen atom abstractions from these positions are favoured. In addition, abstraction at C 6 would be sterically and statistically favoured.
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June 1, 2005
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The mechanism by which the carbonate radical anion reacts with D-glucose in alkaline aqueous solutions has been studied by means of γ-radiolysis. From the product analysis it is concluded that the reaction sequence is initiated by a one-electron transfer between the carbonate radical anion and deprotonated D-glucose. In the presence of molecular oxygen, the major, if not only products of this reaction sequence are formic acid, arabinose and gluconic acid and reaction schemes are proposed to account for the observed formation of these products.
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June 1, 2005
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Solid-state NMR spectroscopy was used to determine total lignin and to distinguish between the syringyl and guaiacyl components of Phormium leaves. Fibers obtained from the upper (shiny) and lower (dull) surfaces of a P. tenax leaf showed guaiacyl lignin contents of 1.5% and 5.4% by weight, respectively. Guaiacyl lignin is known to have poor photostability, so the analyses supported a traditional view of the upper-surface fibers as the more suitable for textiles. All other analyses involved mixtures of fibers from both upper and lower surfaces. They showed no detectable differences in guaiacyl content between leaves within a ramet, or between ramets in a P. tenax bush, with a mean value of 2.2% for 20 leaves. There were no detectable differences in guaiacyl content between bushes of the variety Taeore grown at different sites, with a mean value of 2.7% for 6 sites. There were detectable differences in guaiacyl content between 15 named varieties grown at a single site, with values as low as 2.3% and as high as 4.5%. Lowest guaiacyl contents were found in varieties traditionally used for textiles. The highest guaiacyl lignin contents, 6.0% and 5.8%, were found in P. cookianum and in a plant grown from stock obtained at Norfolk Island. Syringyl lignin contents were relatively uniform between varieties, with a mean value of 6.7%.
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June 1, 2005
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June 1, 2005
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The total phenolic content and antioxidant activity of extracts from pine species were evaluated for various plant components, with emphasis on the seed cones. Seed cones from pine species were found to contain relatively high amounts of both total phenolics and antioxidant activity, and there appears to be some correlation of the two measurements. Juvenile cones contained by far the highest phenolic and antioxidant activity, but this high activity appears to be related to seeds retained in some of the samples, possibly due to the presence of proteins or additional antioxidants in the seeds. The phenolic content and antioxidant activity were also measured for other plant components and for a few other species for comparison. In general, the cones of red and jack pine exhibited the highest antioxidant activity compared to black and southern pines. The general trend for both total phenolics and antioxidant activity was (highest to lowest): juvenile cones>needles>new cones> bark>old cones>wood. Obviously, cones could represent a viable source of antioxidants, especially compared to the wood of species that had comparatively low activity. Collection and extraction of pine cones for antioxidants would be a non-destructive method for procurement of this medicinal aid.
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June 1, 2005
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Wood “cell-wall deformation” is a comprehensive term describing any physical dislocation in the wall caused by mechanical forces. The development and effect of fibre dislocations on wood fibres, and their ultimate impact on the mechanical properties of paper remain rather obscure and controversial. Dislocations are difficult to quantify through a lack of defined measurable features, and research is aggravated by the inherent difficulties of applying statistical tools. A direct approach for studying the effect of dislocations on the mechanical properties of paper was used in this study. Dislocations in fibre cell walls were introduced by exposing whole wood fibres in mature and juvenile wood samples to compression stress. Sapwood samples of Norway spruce ( Picea abies Karst.) were loaded by compression to their ultimate strength using an Alwetron-50 universal testing machine. Failure of samples conditioned to a moisture content of 9–15% always occurred in an oblique (relative to the fibre axis) plane and all fibres in the plane were deformed. When samples were loaded in a wet condition (i.e., moisture content close to the fibre saturation point), failure occurred at one end of the samples, resulting in highly disorganised fibres. Pulp and paper from the compressed fibres were produced and the mechanical properties of the paper were tested. Results of the mechanical tests were compared statistically to results derived from paper made from matched non-compressed control samples. Morphological features of fibres and dislocations after compression failure were characterised using microscopy (scanning electron microscopy, polarised light) on the whole wood and macerated fibres before and after paper testing. The above experimental approach showed that paper made from control samples had significantly better mechanical properties than paper made from samples loaded by compression under dry or wet conditions. At a tensile index of 90 N m/g, the tear index was measured as 23.6 mN m 2 /g for controls, while the corresponding values for compressed wet wood samples was 12.6 and 16.3 mN m 2 /g for samples at 9–15% moisture content. Paper made from juvenile wood also showed lower mechanical properties compared to controls. The results prove the negative effect of dislocations on the mechanical properties of paper in the worst case scenario and are of practical importance.
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June 1, 2005
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The actinobacterium Streptomyces cyaneus CECT 3335 was evaluated for its ability to delignify spruce wood chips ( Picea abies ) after 2 weeks of incubation prior to refiner mechanical pulping. Weight loss of the chips during the treatment ranged from 2% to 3%. Chemicalanalysis of the treated wood showed an increase in acid-soluble lignin content concomitant with a notable increase in the acid/aldehyde+ketone [AC/(AL+KE)] ratio of the lignin compared with the control. Structural alterations in wood cell walls were observed by optical and scanning microscopy using astra blue-safranin staining and cryosections stained with gold/palladium, respectively. A gradual loss of lignin from the lumen towards the middle lamella and incipient defiberization could be observed. The estimation of specific energy for the defibration and refining stages of treated pulp showed a 24% reduction in the energy required, largely due to a 30% saving in the defibration of chips. The analysis of handsheets obtained from treated pulp showed a notable improvement in some strength properties, such as breaking length, tear index and stretch. In addition, the high Gurley air resistance value indicates more packing of the voids of the fiber network. These results demonstrate for the first time the suitability of Streptomyces cyaneus for biomechanical pulping purposes.
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June 1, 2005
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Archaeological wood from waterlogged environments is mainly degraded by erosion bacteria. Under the light microscope, a distinct chequered decay pattern is often found in superficially to moderately degraded wood. Serial sections of Pinus sylvestris , degraded by erosion bacteria, were examined to gain an understanding of this phenomenon. An advanced image analysis program was used to transform series of 2-dimensional (2-D) images from attacked fibres into 3-D illustrations in order to visualise variations in decay along 340 μm of the tracheid. Degradation by erosion bacteria proceeded from the cell lumen into the secondary cell wall. Attack was initiated at several positions in the same tracheid. The chequered pattern observed in transverse sections, often referred to as degraded fibres adjacent to sound ones, shows only the decay status at the section point. A sound cell wall does not necessarily indicate a sound fibre. A fibre in moderately degraded wood often consists of both degraded and sound areas.
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June 1, 2005
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The durability of 566 Scots pine ( Pinus sylvestris ) samples was tested during a period of 9 years of exposure to weather in Sweden. The parameters investigated were heartwood/sapwood, origin, surface treatment, end-seal, storage and drying method, annual ring width and density. The weight was measured on 67 occasions during 9 years in order to assess the moisture content of the samples. The mass loss was determined for each sample at the end of the trial. Sapwood had a higher moisture uptake and a higher mass loss compared with heartwood. Even if sapwood was painted with an impermeable paint and then end-sealed, it still had higher average moisture content than heartwood. The results also demonstrated that sapwood was more sensitive to different handling conditions than heartwood. Sapwood was sensitive to air-drying and water storage, which was evident in the higher moisture uptake. In terms of mass loss, some differences were evident but they were not statistically significant due to the large standard deviation of the sapwood samples from water-stored logs. The only positive influence of water storage was on samples end-dipped in oil. One explanation could be that water storage led to increased permeability due to bacterial attack, which in turn enhanced the penetration of the oil. Heartwood had low and stable moisture dynamics during the test period, almost independent of treatment or handling conditions. No correlation with moisture uptake or mass loss was evident among annual ring width, origin or density.
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June 1, 2005
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This study examined the effect of cation and anion chemical structure of new quaternary ammonium and imidazolium compounds (QAC, bis-QAC, IC, bis-IC) on the adsorption onto Scots pine wood ( Pinus sylvestris L.) and resistance to water leaching. The group of copper (II) modified QACs, containing copper-chloro-acetate complexes in the anion structure, was also examined. The length of alkyl hydrophobic substituents in the cation structure significantly influences adsorption. The adsorption characteristics were statistically related to the alkyl chain length of new quaternary ammonium salts (quantitative correlations between CMC and adsorption values). Bis-ICs adsorb onto Scots pine wood with the greatest difficulty and the slowest and are also leached to the greatest degree. A varied adsorption of chloride ion cations and a several times higher leaching of chlorides than cations of the examined salts from the saturated wood were observed. The anion modification of bis-QAC and bis-IC of copper-chloro-acetate complexes causes decreased adsorption and resistance to the leaching of these salts. As a result of the performed regression analysis of Langmuir and Freundlich adsorption isotherms, it was found that the adsorption of the examined compounds onto wood was governed by both chemical and physical processes. New quaternary ammonium and imidazolium compounds represent potential wood preservatives.
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February 1, 2005
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A 558-h laboratory leaching test (AWPA E-11) was carried out on both commercially and laboratory chromated copper arsenate (CCA) type C-treated southern pine. Arsenic, chromium, and copper concentrations in the leachate collected were examined. Leaching of chromium and copper from CCA-treated wood cubes were nearly undetectable using flame atomic absorption spectroscopy after 174 and 366 h, respectively. Less than 10% of the total chromium in the leachate was present as hexavalent chromium [Cr(VI)] after leaching for 30 h. Selective ion-exchange chromatography was used to speciate arsenic in the leachate. In the first 270 h, approximately 70–90% of the total arsenic in the leachate was inorganic pentavalent arsenic [As(V)] and 10–30% was inorganic trivalent arsenic [As(III)].
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February 1, 2005
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We previously found that a combination of various organic biocides with low-cost non-biocidal antioxidants gave enhanced (synergistic) efficacy against wood-decaying fungi. The best laboratory results were obtained with propyl gallate, perhaps due to its dual antioxidant/metalchelating properties. In this study we report on potentiometric titration experiments for the complexation of Fe 2+ with propyl gallate. The results suggest four coordination compounds are present in the pH range from 3 to 12. These are [(H 2 PG)Fe] + , (HPG)Fe, [(PG)Fe] − , and [(HPG) 2 Fe] 2− {PG=O 3 C 6 H 2 CO 2 CH 2 CH 2 CH 3 3− }. Equilibrium constants for the formation of all complexes are given. A plot of species present versus pH clearly indicates that propyl gallate strongly complexes with Fe 2+ at the mildly acidic pH levels normally present in wood, with some complexing still possible in relatively acidic environments present in decaying wood. Propyl gallate complexes more strongly than catechol at the pH values of normal wood. Propyl gallate may also interfere with the proposed fungal redox cycles. Metal complexation may thus be an important part in the overall mechanism by which propyl gallate and organic biocides synergistically protect wood. Furthermore, the metal chelating properties of heartwood extractives, such as the hydrolysable tannins from which propyl gallate is made, may be an important factor in natural durability.
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February 1, 2005
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When a radial strip is cut from an increment core it can potentially be cut with two orientations: parallel to longitudinal tracheids, i.e., a radial-longitudinal (RL) strip (the orientation of SilviScan samples), or at an orientation of 90° to the tracheids, i.e., a radial-transverse (RT) strip. Both strips could be used for near-infrared (NIR) analysis, but it is unknown how calibrations based on RT-face NIR spectra compare with those based on RL-face NIR spectra. A total of 20 Pinus taeda L. (loblolly pine) RL strips were characterized in terms of air-dry density, microfibril angle (MFA), stiffness and several tracheid morphological characteristics. NIR spectra were collected in 10-mm increments from the RL and RT faces of matching strips and used to develop calibrations for each property. In general, RL-face NIR spectra gave calibrations that provided stronger relationships. Differences between the two sets of calibrations were small, indicating that either face could be used for NIR analysis.
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February 1, 2005
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Wooden glued constructions require touch-free monitoring of destructive processes, especially in adhesive bonds that are most exposed to failure. The objective of the investigations was to describe failure processes in the adhesive bond of wood joints, in particular to determine their initiation, propagation, and destruction. The acoustic emission (AE) method was employed as the carrier of information about changes occurring in glued joints, whereas the numerical method was applied to determine values of distribution of tangential stresses generated in adhesive bonds. The acoustic phenomena examined were described using the AE cumulative counts. The authors analysed acoustic signals generated in loaded wooden and plastic overlap samples glued together using polyethyl methacrylate glue as well as in solid samples. On the basis of the acoustic emissions obtained, it was possible to establish characteristic places and stages of escalating structural defects generated from bonds of adhesive joints. This was utilised later on, in conjunction with results of numerical calculations, to determine correlations occurring between the AE cumulative counts and generated tangential stresses. Dependencies established in this way were used to determine characteristic points during the propagation of destructive phenomena of wood adhesive joints. The results obtained proved that it was possible to predict the development of the destruction of wood adhesive joints on the basis of observations of the increasing AE cumulative counts of acoustic signals in combination with tangential stresses determined using the finite elements method.
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February 1, 2005
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When wood is subjected simultaneously to load and moisture content changes below the fiber saturation point, the mechano-sorptive effect may be observed as an additional deformation that cannot be attributed to simple superposition of elastic deformation, free shrinkage or swelling, or creep in steady climate conditions. The phenomenon has been subject to research for more than half a century. Although numerous mathematical models and detailed theoretical descriptions have been proposed over time, the basic mechanism of mechano-sorption has remained unclear, the experimental data are scattered and lack logical classification, and the experimental determination of its basic parameters on a material level, understood as a local property decoupled from artifacts of the testing protocol, remains a serious challenge. In this paper basic requirements for adequate experimental methods for comprehensive determination of the mechano-sorptive behavior of wood are proposed and briefly discussed. The principal requirements are that the experimental research on mechano-sorption is focused on the material level properties and elementary loading modes (tension and compression); that proper attention is paid to the effect of changing distribution of moisture content within the tested volume; and that the tests are designed so that a comprehensive separation of strain components is enhanced.
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February 1, 2005
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Single fibres of spruce ( Picea abies [L.] Karst.) were isolated both chemically and mechanically from a solid wood sample. Mechanical isolation was carried out using very fine tweezers to peel out fibres, thereby taking advantage of the low shear strength between them. Chemical isolation was achieved using hydrogen peroxide and glacial acetic acid. Fibres were examined with Fourier-transform infrared (FT-IR) microscopy, and field-emission environmental scanning electron microscopy (FE-ESEM) in low-Vacuum mode to compare the isolation techniques with respect to their influence on cell wall structure and polymer assembly. The chemical treatment led to degradation of lignin and hemicelluloses, significantly influencing the cell wall assembly and structure. The cell wall polymers of mechanically isolated fibres remained in their natural constitution. As expected, the peeling process caused separation of cell wall layers. Our examinations indicate that delamination predominately took place at the interface between the secondary cell wall and the compound middle lamella. However, fracture between the S1 and S2 layers was examined as well. With respect to fibre quality, it was of particular importance that transverse crack propagation in the secondary cell walls (S2) was not observed.
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February 1, 2005
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The twisting behaviour of chemically and mechanically isolated fibres of spruce ( Picea abies [L.] Karst.) was examined. Mechanical isolation was carried out using very fine tweezers to obtain fibres with an unmodified cell wall assembly. Chemical isolation was achieved using hydrogen peroxide and glacial acetic acid, leading to partial degradation of lignin and hemicelluloses. Besides normal adult wood, compression wood and opposite wood fibres were investigated. Fibre twisting while drying increased with higher microfibril angles in the S2 layer, and was significantly less pronounced for mechanically isolated compared to chemically macerated fibres. A simple model is introduced that takes into account the interdependency between lateral cell-wall shrinkage and the microfibril angle in the S2 cell wall.
