| 1. |
- Ahrenstedt, Lage, et al.
(författare)
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Paper dry strength improvement by xyloglucan addition: Wet-end application, spray coating and synergism with borate
- 2008
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 62:1, s. 8-14
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Tidskriftsartikel (refereegranskat)abstract
- The polysaccharide xyloglucan as a wet-end additive improves paper properties. In the present study, paper strength improvement was analysed for dry handsheets made from chemical, mechanical and recycled pulps coated with xyloglucan in a spray application. Results are compared with sheets made from the same pulps treated with xyloglucan in the wet-end. Kraft pulp handsheets of bleached hardwood and softwood showed significant improvements of tensile, tear and Z-strength by xyloglucan spray treatment versus wet-end application, whereas handsheets of de-inked and thermomechanical pulp were improved only slightly. In both wet-end and spray applications, the effect of xyloglucan addition was intimately related to the presence of non-cellulosic components on the fibre surface. Further strength improvements were obtained for chemical pulps by addition of borax to the spray solution, which were likely to be due to the formation of borate-mediated xyloglucan cross-links. Spray coating of xyloglucan, with or without borax, thus represents a potential new application of this polysaccharide to increase paper dry strength.
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| 2. |
- Baumberger, Stephanie, et al.
(författare)
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Molar mass determination of lignins by size-exclusion chromatography : towards standardisation of the method
- 2007
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 61:4, s. 459-468
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Tidskriftsartikel (refereegranskat)abstract
- The reactivity and physicochemical properties of lignins are partly governed by their molar mass distribution. The development of reliable standard methods for determination of the molar mass distribution is not only relevant for designing technical lignins for specific applications, but also for monitoring and elucidating delignification and pulping processes. Size-exclusion chromatography (SEC) offers many advantages, such as wide availability, short analysis time, low sample demand, and determination of molar mass distribution over a wide range. A collaborative study has been undertaken within the Eurolignin European thematic network to standardise SEC analysis of technical lignins. The high-molar-mass fraction of polydisperse lignins was shown to be the main source of intra- and interlaboratory variations, depending on the gel type, elution solvent, detection mode, and calculation strategy. The reliability of two widespread systems have been tested: one based on alkali and a hydrophilic gel (e.g., TSK Toyopearl gel) and the other based on THF as solvent and polystyrene-based gels (e.g., Styragel). A set of practical recommendations has been deduced.
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| 3. |
- Berg, Jan-Erik, et al.
(författare)
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On the energy consumption for crack development in fibre wall in disc refining - A micromechanical approach
- 2009
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 63:2, s. 204-210
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Tidskriftsartikel (refereegranskat)abstract
- An analytical model has been applied to calculate the acquired strain energy density in order to achieve a certain damage state in a softwood fibre by uniaxial tension or shear load. The energy density was found to be dependent on the microfibril angle in the middle secondary wall, the loading case, the thicknesses of the fibre cell wall layers, and conditions such as moisture content and temperature. At conditions, prevailing at the entrance of the gap between the plates in a refiner and at relative high damage states, more energy is needed to create cracks at higher microfibril angles. The energy density was lower for earlywood compared to latewood fibres. For low microfibril angles, the energy density was lower for loading in shear compared to tension for both earlywood and latewood fibres. Material parameters, such as initial damage state and specific fracture energy, were determined by fitting of input parameters to experimental data.
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| 4. |
- Blom, Åsa, et al.
(författare)
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Mass loss and moisture dynamics of Scots pine (Pinus sylvestris L.) exposed outdoors above ground in Sweden.
- 2005
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 59:2, s. 183-189
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Tidskriftsartikel (refereegranskat)abstract
- 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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| 5. |
- Blomberg, Jonas, et al.
(författare)
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Effects of semi-isostatic densification on anatomy and cell-shape recovery on soaking
- 2006
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 60:1, s. 322-331
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Tidskriftsartikel (refereegranskat)abstract
- Images obtained by scanning electron microscopy (SEM) helped to clarify the question as to how anatomy influences the deformation on compression and the spring-back of densified wood on water soaking. Transverse sections of Norway spruce (Picea abies), Scots pine (Pinus sylvestris), black alder (Alnus glutinosa), Swedish aspen (Populus tremula), European birch (Betula pubescens), European beech (Fagus sylvatica) and pedunculate oak (Quercus robur) were studied. Wood is reinforced with rays in the radial direction and with dense latewood in the tangential direction. When strained radially, rays buckle or tilt tangentially. Softwoods were mainly compressed radially, owing to low number of rays and since latewood is much denser than earlywood. The diffuse-porous hardwoods with low density variation between latewood and earlywood were mainly deformed tangentially, except birch, which has high density at the annual ring border and is mainly compressed radially. The ringporous hardwoods were relatively equally deformed in the radial and tangential directions because of the high number of rays and high latewood density. Moisture-induced springback (shape recovery) was proportional to the degree of compression. Rays remained deformed, which also influenced the surrounding wood. Longitudinal wood cells almost resumed their original shape. Wood with low density and a low degree of compression showed the highest structural recovery. Shearing deformation was particularly pronounced and permanent in woods with high strength anisotropy. Thin-walled and sheared cells, such as earlywood in softwood, tended to crack on compression. Cracks usually stopped at the middle lamella and had a lesser influence on strength properties than for lumen-to-lumen cracks. Copyright
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| 6. |
- Bogren, Johannes, 1979, et al.
(författare)
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Impact of dissolved sodium salts on kraft cooking reactions
- 2009
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Ingår i: Holzforschung. - 1437-434X .- 0018-3830. ; 63:2, s. 226-231
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Tidskriftsartikel (refereegranskat)abstract
- This study examined the effects of inactive ions - ions not reacting with wood - during kraft cooking, which thus far have received modest attention. Six different sodium salts were added to kraft cooking liquors at two different levels of alkalinities. Delignification as well as the formation and degradation of hexenuronic acid (HexA) were observed of Scots pine sapwood meal. The delignification rate was greatly affected by the presence of additional anions. Chloride ions had the greatest retarding effect, while the addition of polyacrylate ions had almost no effect. When carbonate, sulphate and lactate ions were added to the liquors, the delignification rates were in-between the series with chloride and polyacrylates ions. We suggest that the anions affect the solubility of lignin fragments in analogy to the Hofmeister effect observed in various macromolecular systems in the presence of dissolved salts. When the reactions involving HexA were examined, the opposite results were obtained. In that case, the highest reaction rates were in the presence of chloride ions, and the lowest rates were obtained when no extra ions were added, and the second lowest rates were obtained in the presence of polyacrylate ions. As for delignification, the cooking series containing carbonate, sulphate and lactate ions had a reaction rate in-between the series with the highest and lowest rates. The differences obtained with various inorganic ions can be qualitatively explained by the Donnan equilibrium theory and by the variation in activity coefficients of hydroxide ions. Findings imply that knowledge of kraft cooking is far from complete. The effects of inactive ions on reaction kinetics should also receive more attention. © 2009 by Walter de Gruyter.
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| 7. |
- Brodin, Ida, et al.
(författare)
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Kraft lignin as feedstock for chemical products : The effects of membrane filtration
- 2009
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 63:3, s. 290-297
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Tidskriftsartikel (refereegranskat)abstract
- The use of technical lignins as feedstock for chemical products will require improvements in purity, molecular mass distribution, and thermal behavior. Therefore, industrial black liquors from kraft pulping of softwood (spruce/ pine) and hardwood (birch and Eucalyptus globulus) have been subjected to fractionation according to molecular mass by ceramic membranes. After acidification and isolation of the lignin fractions, a variety of analytical methods have been applied to help understand their structure - property relationships. From all types of lignin, the chemical and polymeric properties of fractions isolated from the membrane permeates were more homogeneous. This demonstrates that technical kraft lignins, irrespective of origin, may constitute an interesting feedstock for products, such as carbon fibers, adhesives, and phenol-based polymers.
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| 8. |
- Brodin, Ida, et al.
(författare)
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Kraft lignin as feedstock for chemical products : The effects of membrane filtration
- 2009
-
Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 63:3, s. 290-297
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Tidskriftsartikel (refereegranskat)abstract
- The use of technical lignins as feedstock for chemical products will require improvements in purity, molecular mass distribution, and thermal behavior. Therefore, industrial black liquors from kraft pulping of softwood (spruce/pine) and hardwood (birch and Eucalyptus globulus) have been subjected to fractionation according to molecular mass by ceramic membranes. After acidification and isolation of the lignin fractions, a variety of analytical methods have been applied to help understand their structure - property relationships. From all types of lignin, the chemical and polymeric properties of fractions isolated from the membrane permeates were more homogeneous. This demonstrates that technical kraft lignins, irrespective of origin, may constitute an interesting feedstock for products, such as carbon fibers, adhesives, and phenol-based polymers.
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| 9. |
- Bäckström, Marie, et al.
(författare)
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Characterisation of fines from unbleached kraft pulps and their impact on sheet properties
- 2008
-
Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 62:5, s. 546-552
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Tidskriftsartikel (refereegranskat)abstract
- Fines are an essential component in the papermaking process because they have a profound influence on the behaviour of the wet web and on the mechanical properties of the final sheet. Primary fines are present in the pulp prior to refining, and secondary fines are produced during refining. In the present investigation, two commercially manufactured unbleached pulps with kappa numbers of 45 and 90 were studied in terms of how they responded to refining with respect to the quality of fibre and fines. Primary and secondary fines were collected and characterised and their impact on sheet strength was evaluated by addition of known amounts to a refined and decrilled pulp. All the measured paper strength properties improved when primary and secondary fines were added. The strength improvement was generally somewhat higher in the second case. The effect was more pronounced at a higher level of addition. We attribute the main strength improvements associated with fines to improved consolidation by the creation of capillary forces between the surfaces.
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| 10. |
- Carlsson, Magnus, et al.
(författare)
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A comparative study on the degradation of cotton linters induced by carbonate and hydroxyl radicals generated from peroxynitrite
- 2005
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 59:2, s. 132-142
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Tidskriftsartikel (refereegranskat)abstract
- Carbonate (CO3.(-)) 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 NaBH4 treatment before measuring the viscosity, whereas only approximately 40% of the viscosity was recovered after hydroxyl radical degradation and subsequent NaBH4 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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| 11. |
- Carlsson, Magnus, et al.
(författare)
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A selectivity study of reaction of the carbonate radical anion with methyl beta- D-cellobioside and methyl beta-D-glucoside in oxygenated aqueous solutions
- 2006
-
Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 60:2, s. 130-136
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Tidskriftsartikel (refereegranskat)abstract
- In the presence of oxygen, radiolytically generated carbonate radical anions, CO3.-, were reacted with methyl beta-D-cellobioside and methyl beta-D-glucoside. From the ensuing product pattern, it was concluded that CO3 center dot- abstracts hydrogen atoms predominantly from glucosidic C1 - H bonds. This high intramolecular selectivity was rationalised mainly in terms of a polar effect on the transition state of the hydrogen abstraction reaction. The present findings are in sharp contrast to the relative inertness of CO3(center dot-) towards glucosidic C1 - H bonds previously observed in cotton linters. The reasons for this discrepancy are discussed in light of a possible future role of CO3 center dot- as a bleaching agent for pulp.
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| 12. |
- Carlsson, Magnus, et al.
(författare)
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The Carbonate Radical as One-Electron Oxidant of Carbohydrates in Alkaline media
- 2005
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 59:2, s. 143-146
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Tidskriftsartikel (refereegranskat)abstract
- The mechanism by which the carbonate radical anion reacts with D-glucose in alkaline aqueous solutions has been studied by means of gamma-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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| 13. |
- Daniel, Geoffrey, et al.
(författare)
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Morphological and chemical characterisation of the G-layer in tension wood fibres of Populus tremula and Betula verrucosa : Labelling with cellulose-binding module CBM1(HjCel7A) and fluorescence and FE-SEM microscopy
- 2006
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 60:6, s. 618-624
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Tidskriftsartikel (refereegranskat)abstract
- The gelatinous layer (G-layer) formed on the lumen wall in early- and latewood fibres of poplar and birch tension wood was characterised using a novel molecular marker specific for crystalline cellulose in conjunction with fluorescence and FE-SEM microscopy. Crystalline cellulose was localised using a cloned Cel7A cellulose-binding module (CBM1(HjCel7A)) from the fungus Hypocrea jecorina conjugated directly to FITC/TRITC or indirectly via a secondary antibody conjugated to FITC for fluorescence microscopy or to gold/silver for FE-SEM. With the CBM1(HjCel7A) conjugate, the G-layer was clearly distinguished from other secondary cell-wall layers as a bright green layer visible in fibres of tension wood in fluorescence microscopy. FEM-SEM images revealed the supramolecular architecture of the G-layer of poplar wood, which consists of well-defined, often concentrically orientated, cellulose aggregates of the order of 30-40 nm. The cellulose aggregates typically have a microfibril angle of almost 0 degrees. Studies on cellulose marked with CBM1(HjCel7A) followed by Au labelling and Ag enhancement complemented the fluorescence observations. The studies demonstrate the usefulness of this novel molecular marker for crystalline cellulose in situ, which was previously difficult to localise. Further proof of distinct cellulose aggregates was observed.
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| 14. |
- De Magistris, Federica, et al.
(författare)
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Combined shear and compression analysis using a modified Iosipescu shear test device : Experimental studies on dry wood
- 2005
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 59:5, s. 539-545
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Tidskriftsartikel (refereegranskat)abstract
- The mechanical treatment of wood in a refiner involves a complex combination of shear and compression forces. To obtain more knowledge on this process, the possibility of using an apparatus based on the Iosipescu shear test device to measure the behaviour of wood under a combined shear and compression load was tested. In this new apparatus, different combinations of shear and compression load were achieved by different rotations of the shear test device itself. Numerical simulations of the combined shear and compression test were carried out and compared with experimental data to verify the reliability of the modified device as applied to wood. It was concluded that the new apparatus is suitable for applying different combinations of shear and compression load in testing wood samples. However, finite element analysis showed that with the use of homogeneous material in the model, the level of strain reached would be 10-fold smaller. This fact is probably due to the honeycomb structure of the wood cells, which allows for different local deformation that could not be represented by the continuous material used in the model.
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| 15. |
- Elustondo, Diego, et al.
(författare)
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Temperature-drop sensor for determination of drying curves in conventional lumber drying
- 2006
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 60:2, s. 196-200
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Tidskriftsartikel (refereegranskat)abstract
- Conventional lumber drying is carried out by forcing hot air to flow across a pile of lumber layers separated by wood strips. The airflow provides the heat required to warm up the lumber and produce the moisture evaporation and, in theory, the difference in temperature at each side of the load can be used to estimate the evaporation rate. The main problem with this approach is that typical temperature sensors that are installed in conventional kilns are not accurate enough to measure the temperature drop across the load during periods of low evaporation. In this paper, a new sensor to measure the temperature drop across the load is proposed and tested in three experimental drying runs of 2" X 6" spruce-pine lumber. The results demonstrate that after calibration, the temperature drop across the load can be used to determine drying curves in conventional lumber drying. In the particular case of this study, calibration was performed by multiplying the experimental temperature drop across the load by a constant factor, which was adjusted by identifying the correction factor that best simulated the experimental green moisture content of the three lumber charges.
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| 16. |
- Elustondo, Diego, et al.
(författare)
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Temperature drop sensor for monitoring kiln drying of lumber
- 2009
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 63:3, s. 334-339
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Tidskriftsartikel (refereegranskat)abstract
- The main objective of this study was to test a new sensor based on the temperature drop across the load (TDAL). The TDAL sensor was designed to determine the transition point between wet and dry wood without any specific information about the drying process. When additional information is available, the TDAL sensor can also be used to monitor drying rate and estimate the drying end-point. In this study, three potential applications of TDAL sensor for lumber drying were explored, namely, to monitor drying rate, to detect the transition point between wet and dry wood, and for determination of drying end-point after calibration. For the first application, it was demonstrated that the transition point between wet and dry wood coincides with the time at which the TDAL decreases with time at a constant logarithmic slope. For the second application, the TDAL sensor was calibrated with nine experimental drying runs, and the end-points determined with the calibrated TDAL sensor did not show a significant difference with the end-points determined by the in-kiln MC meter. Finally, the TDAL sensor was used to monitor drying rate during drying
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| 17. |
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| 18. |
- Fahlén, Jesper, et al.
(författare)
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Ultrastructural changes in a holocellulose pulp revealed by enzymes, thermoporosimetry and atomic force microscopy
- 2005
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 59:6, s. 589-597
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Tidskriftsartikel (refereegranskat)abstract
- To increase our knowledge of the ultrastructure within softwood fibres, enzymatic treatment, thermoporosimetry, light microscopy, and atomic force microscopy with image analysis were used to investigate the structure of holocellulose softwood pulp fibres. The size of the average cellulose fibril aggregates and the width of pore and matrix lamellae were found to be uniform across the secondary cell-wall layer in the transverse direction of the wood fibre wall. In holocellulose, these dimensions were very similar to those in the native wood, whereas in kraft pulp the cellulose fibril aggregates were larger and the pore and matrix lamellae broader. These differences between holocellulose and kraft pulp fibres suggest that a high temperature is needed for cellulose fibril aggregation to occur. Neither refining nor drying of the holocellulose pulp changed the cellulose fibril aggregate size. Upon drying and enzymatic treatment, a small decrease in the pore and matrix lamella width was evident throughout the fibre wall. This indicated not only uniform distribution of pores throughout the fibre wall, but also enzymatic accessibility to the entire fibre wall. The holocellulose pulp had a somewhat larger pore volume than the kraft pulp. Refining of the holocellulose pulp led to pore closure, probably due to increased mobility of the fibre wall. The enzymatic treatment revealed that during hydrolysis of one hemicellulose, part of the other was also dissolved, indicating that the two hemicelluloses are to some extent linked to each other in the structure.
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| 19. |
- Fardim, P, et al.
(författare)
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Critical comparison of methods for surface coverage by extractives and lignin in pulps by X-ray photoelectron spectroscopy (XPS)
- 2006
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 60, s. 149-155
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Tidskriftsartikel (refereegranskat)abstract
- Different methods for estimation of the surface coverage by extractives and lignin were critically compared. For data collection, four state-of-the-art X-ray photoelectron spectroscopy (XPS) instruments located in four different laboratories were used. Hand sheets of one mechanical and two chemical pulp samples were prepared in one laboratory and distributed among the other participants. The XPS results based on O/C ratios and curve fitting of the C 1s peak had very good intra- and interlaboratory variation for extracted and non-extracted pulp samples. The estimations of surface coverage by extractives and lignin also had acceptable intra- and interlaboratory variation. However, significant differences were observed between the results for the various methods. Estimation of surface coverage by extractives based on O/C ratios was much higher than that based on the C1 component analysis in the case of mechanical and unbleached chemical pulp. The surface coverage by lignin of mechanical pulp was reproducibly detected based on O/C ratios, C1 component analysis and by labelling with mercury acetate. The same data were, however, rather scattered if they were collected with these three methods for bleached and unbleached chemical pulp. In spite of the differences, similar trends regarding the pulp type could be observed. We interpret the results as indicating that the surface coverage for both extractives and lignin should not be considered as absolute “true” values, but rather as relative values, which are reliable only for comparison of samples for the same instrument. Even for relative comparisons, we recommend the selection of a strict experimental set-up for spectral acquisition and data treatment when applying any of the instruments and calculation models currently available.
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| 20. |
- Heijnesson Hultén, A, et al.
(författare)
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Comparison of different XPS methods for fiber surface analysis
- 2006
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 60:1, s. 14-19
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Tidskriftsartikel (refereegranskat)abstract
- Three different XPS methods based on the O/C atomic ratio, C1 carbon content, and Hg amount are compared in this study to quantify the surface coverage of various pulp fiber surfaces by lignin and extractives. The sensitivity of the methods to drying technique and the stability of organically bound mercury when subjected to X-ray irradiation were also investigated. Results reveal that the surfaces of all pulp fibers have a higher content of lignin and extractives than the bulk of the fibers. Similar lignin surface coverage was obtained for thermomechanical pulp fibers using the Hg, O/C, and C1 carbon methods, while the Hg method gave lower values for kraft pulp fibers than the O/C and C1 carbon methods. The O/C and C1 carbon methods are sensitive to the drying technique, i.e., air-dried samples showed a higher amount of lignin on the fiber surface than freeze-dried samples, while no or only minor differences in results were obtained using the Hg method. The Hg method was more reproducible than the other methods. Special care must be exercised during XPS analysis to minimize mercury degradation.
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| 21. |
- Henriksson, Gunnar, et al.
(författare)
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Lignin-carbohydrate network in wood and pulps : A determinant for reactivity
- 2007
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 61:6, s. 668-674
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Tidskriftsartikel (refereegranskat)abstract
- Pretreatment of wood or kraft pulp with endoglucanase followed by swelling in urea leaves a non-crystalline residue that can be dissolved in strong aqueous sodium hydroxide-sodium borate solution. A stepwise precipitation process employing acid and barium ions can separate lignin-carbohydrate complexes enriched in individual polysaccharides. This procedure has been applied to eucalypt and birch wood and to the corresponding kraft pulps. Thioacidolysis of the various lignin-carbohydrate complexes was used as the major analytical technique to obtain information about the structure and structural changes in lignin. A combination of thioacidolysis and size exclusion chromatography was used to obtain knowledge on the degree of depolymerisation and repolymerisation of lignin when going from wood to chemical pulp. In contrast to spruce wood and kraft pulp, complete recovery of the lignin-carbohydrate complexes could not be obtained from hardwood samples.
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| 22. |
- Hildén, Lars, et al.
(författare)
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Distribution and characterization of discolouring substances in Norway spruce (Picea abies L.Karst) pulp wood stored under water-sprinkling
- 2006
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 60:1, s. 93-98
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Tidskriftsartikel (refereegranskat)abstract
- Discolouration of wood raw material during wet storage has a notable negative effect on the quality of the final product. In this study, fluorescence microscopy was used to investigate the spatial distribution of discolouring substances in water-sprinkled Norway spruce pulpwood. Water-sprinkled wood was characterised by the presence of discolouring substances on the pit membranes of wood cells. In vitro model studies on the interaction between a model bark substance (tannic acid) and torus constituents support the hypothesis that pectic structures facilitate the allocation of bark substances on pit membranes. Applied pectinase or tannase could not remove the discolouring substances from pit membranes. Manganese peroxidase had a minor but documented effect. The effect of manganese peroxidase, as well as HCl/vanillin labelling, indicated that the discolouring substance may be condensed tannins.
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| 23. |
- Hofstetter, Karin, et al.
(författare)
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Hierarchical modelling of microstructural effects on mechanical properties of wood. A review COST Action E35 2004-2008 : Wood machining - micromechanics and fracture
- 2009
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 63:2, s. 130-138
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Forskningsöversikt (refereegranskat)abstract
- Wood exhibits a hierarchical architecture. Its macroscopic properties are determined by microstructural features at different scales of observation. Recent developments of experimental micro-characterisation techniques have delivered further insight into the appearance and the behaviour of wood at smaller length scales. The improved knowledge and the availability of increasingly powerful micromechanical modelling techniques and homogenisation methods have stimulated rather comprehensive research on multiscale modelling of wood. Linking microstructural properties to macroscopic characteristics is expected to improve the knowledge of the mechanical behaviour of wood and to serve as the basis for the development of innovative wood-based products and for biomimetic material design. Moreover, understanding fundamental aspects of wood machining requires multiscale approaches which can take into account the heterogeneity, anisotropy and hierarchies of wood and wood composites. In this review, recent developments in the field of hierarchical modelling of the hygroelastic behaviour of wood are discussed, and a short outline of the theoretical background is given. Much focus is placed on composite micromechanical models for the wood cell wall and on multiscale models for wood resting upon hierarchical finite element models and on the application of continuum micromechanics, respectively. These models generally lead to the specification of equivalent homogeneous continua with effective material properties. Finally, current deficiencies and limitations of hierarchical models are sketched and possible future research directions are specified.
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| 24. |
- Holmgren, Anders, et al.
(författare)
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Monolignol dehydrogenative polymerization in vitro in the presence of dioxane and a methylated beta-beta ' dimer model compound
- 2008
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 62:5, s. 508-513
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Tidskriftsartikel (refereegranskat)abstract
- Lignin formation is believed to occur by polymerization of resonance-stabilized monolignol radicals formed by enzymatic oxidation. Recently, different hypotheses suggested that lignin polymerization is influenced by surfaces in the cell wall which can be polysaccharides or proteins. The latter is called the proteinaceous dirigent sites/template polymerization hypothesis. According to another hypothesis, lignin itself is believed to act as a template and replicate its primary structure. In this work, dehydrogenative polymerization (DHP) of the lignin precursor coniferyl alcohol was performed in vitro in the presence and absence of pinoresinol dimethyl ether (a beta-beta ' dimer model). Another peculiarity of the experiments was the presence of dioxane which afforded a high solubility of the reactants. The question was whether the presence of beta-beta ' dimer model would change the structure of the DHP formed. The DHPs were analyzed by quantitative C-13 NMR, GC-FID, and GC-MS. The dimer model as a template in the homogeneous polymerization state (in solution) did not influence the DHP structure.
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| 25. |
- Ibarra, David, et al.
(författare)
-
Exploring enzymatic treatments for the production of dissolving grade pulp from different wood and non-wood paper grade pulps
- 2009
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 63:6, s. 721-730
-
Tidskriftsartikel (refereegranskat)abstract
- The feasibility of producing dissolving grade pulps for viscose production from different fiber raw materials, such as paper grade pulps from wood and non-woody plants, was investigated. Commercial dried bleached hardwood kraft pulps from eucalypt, and bleached non-wood soda/AQ pulps from flax, hemp, sisal, abaca, and jute, were subjected to enzymatic and chemical pretreatments in order to improve the accessibility and reactivity of cellulose and to reduce their hemicellulose content. A commercial monocomponent endoglucanase and a commercial xylanase were employed for biochemical treatment. The chemical treatment consisted of cold alkaline extraction. The effects of these pre-treatments on pulps were studied by reactivity, according to Fock's method, and viscosity measurements, determination of hemicellulose content, and recording of molecular weight distributions. The results were compared to those of commercial bleached eucalypt dissolving pulp. Eucalypt and sisal pulps showed high improvement in reactivity, reaching levels near or even higher than that of the eucalypt dissolving pulp (65%-70%), and a low hemicellulose content (2%-4%), when both were submitted to a sequence of treatments consisting of an initial xylanase treatment followed by cold alkaline extraction, and a final endoglucanase treatment. However, the viscosity decreased considerably. A uniform and narrow molecular weight distribution was observed in both eucalypt and sisal pulps after this sequential pre-treatment.
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| 26. |
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| 27. |
- Jääskeläinen, A-S, et al.
(författare)
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Application of UV-Vis and resonance Raman spectroscopy to study bleaching and photoyellowing of thermomechanical pulps
- 2006
-
Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 60, s. 231-238
-
Tidskriftsartikel (refereegranskat)abstract
- The chemistry of thermomechanical pulp bleaching and brightness reversion was studied. First, UV-Vis reflectance spectroscopy was used to obtain information on the reactive structures in pulp. Based on these data, a Raman excitation wavelength was chosen close to the absorption bands of the chromophores formed to take advantage of the resonance enhancement (resonance Raman spectroscopy). Fluorescence was rejected with a picosecond Kerr gate. The results revealed that coniferyl aldehyde structures were partly removed by alkaline peroxide bleaching and these structures were further degraded during light exposure. However, this reaction was obviously not responsible for chromophore formation in the pulp. On the other hand, based on the resonance Raman spectra, formation of quinonoid structures, possibly para-quinones, was a more prominent explanation for the brightness reversion
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| 28. |
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| 29. |
- Krusa, M., et al.
(författare)
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Oxidative cellulose degradation by cellobiose dehydrogenase from Phanerochaete chrysosporium : A model compound study
- 2005
-
Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 59:3, s. 263-268
-
Tidskriftsartikel (refereegranskat)abstract
- Cellobiose dehydrogenase (CDH) is an extracellular enzyme produced by various wood-degrading fungi. It oxidizes cellobiose to cellobionolactone under reduction of molecular oxygen to hydrogen peroxide, and Fe3+ to Fe2+. These activated agents can thereafter form highly reactive hydroxyl radicals, which depolymerize wood polymers. In this work, cellulose depolymerization by CDH was studied using a model compound, methyl beta-D-glucopyranoside. The formation of glucose, arabinose, gluconic acid, erythrulose and formaldehyde were detected and a mechanism for the reaction is proposed. The biological importance of this enzyme-initiated reaction is discussed.
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| 30. |
- Lawoko, Martin, et al.
(författare)
-
Characterisation of lignin-carbohydrate complexes (LCCs) of spruce wood (Picea abies L.) isolated with two methods.
- 2006
-
Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 60:2, s. 151-161
-
Tidskriftsartikel (refereegranskat)abstract
- A method for the quantitative isolation of lignin-carbohydrate complexes (LCCs) in a softwood is presented. The isolation steps involve partial enzymatic hydrolysis of cellulose, subsequent swelling in urea, and quantitative dissolution into four major fractions: (1) a galacto-glucomannan LCC containing similar to 8% of the wood lignin; (2) a glucane LCC containing similar to 4% of the wood lignin; (3) a xylan-lignin-glucomannan network LCC (xylan > glucomannan) containing similar to 40% of the wood lignin; and (4) a glucomannan-lignin-xylan network LCC (glucomannan) xylan) containing similar to 48% of the wood lignin. Endo-glucanase Novozyme 476, with only cellulase activity, and Ecopulp XM, with only xylanase and mannanase activities, were used as an enzymatic tool. From mildly ball-milled wood, all the lignin was isolated as LCCs. As a control, LCC was prepared from partially chlorite-delignified wood meal without ball milling, also in a mild procedure. The results were very similar to those obtained after ball milling. Thus, it can be safely concluded that the formation of new chemical linkages between lignin and carbohydrates during ball milling is improbable. Studies on isolated milled wood lignin (MWL) supported this conclusion and clearly showed that covalent linkages between lignin and carbohydrates are present. The study provide conclusive evidence of covalent linkages between lignin and carbohydrates in the native lignin in wood. It is concluded that carbohydrate-free lignin, i.e., lignin without covalent bonds to carbohydrates, probably cannot be present in spruce wood.
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| 31. |
- Lawoko, Martin, et al.
(författare)
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Characterization of Lignin-Carbohydrate Complexes from Spruce Sulfite Pulp : Lignin-polysaccharide networks III
- 2006
-
Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 60:2, s. 162-165
-
Tidskriftsartikel (refereegranskat)abstract
- Lignin-carbohydrate complexes (LCCs) were isolated from unbleached acid sulfite pulp by selective enzymatic hydrolysis followed by fiber swelling and extraction. Approximately 80% of the lignin in the pulp was found to be chemically linked to carbohydrates in three major fractions, viz. as one glucan-lignin complex (with 8% lignin) and two hemicellulose-lignin complexes (with 72% lignin). The latter two were further separated into one glucomannan-lignin complex (with similar to 25% lignin) and one xylan-lignin-glucomannan complex (with 45 - 50% lignin). Based on model experiments, it can be concluded that the lignin and carbohydrate moieties are probably linked together through benzyl ether linkages. Xylan is more stable towards acidic hydrolysis than galactoglucomannan, and this finding may explain the greater amount of xylan-rich LCC in the pulp.
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| 32. |
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| 33. |
- Lindfors, Eva-Lisa, et al.
(författare)
-
Polysaccharide degradation in waterlogged oak wood from the ancient warship Vasa
- 2008
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 62:1, s. 57-63
-
Tidskriftsartikel (refereegranskat)abstract
- A rather extensive degradation of cellulose and hemicelluloses was found in waterlogged oak wood samples from the ancient warship Vasa by size exclusion chromatography with the solvent system lithium chloride/ N,N-dimethylacetamide (LiCl/DMAc). The degradation has mainly occurred after salvage of the wreck, probably as a consequence of keeping iron contaminated wood in contact with air. The most likely explanation is Fenton type of reactions degrading the wood polymers and oxidising reduced sulphur forms to sulphuric acid. An increased degradation rate of the Vasa wood can be anticipated in the future if the sulphuric acid cannot be neutralised and the oxidative reactions cannot be quenched.
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| 34. |
- Lindfors, Eva-Lisa, et al.
(författare)
-
Polysaccharide degradation in waterlogged oak wood from the ancient warship Vasa
- 2008
-
Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 62:1, s. 57-63
-
Tidskriftsartikel (refereegranskat)abstract
- A rather extensive degradation of cellulose and hemicelluloses was found in waterlogged oak wood samples from the ancient warship Vasa by size exclusion chromatography with the solvent system lithium chloride/N,N-dimethylacetamide (LiCl/DMAc). The degradation has mainly occurred after salvage of the wreck, probably as a consequence of keeping iron contaminated wood in contact with air. The most likely explanation is Fenton type of reactions degrading the wood polymers and oxidising reduced sulphur forms to sulphuric acid. An increased degradation rate of the Vasa wood can be anticipated in the future if the sulphuric acid cannot be neutralised and the oxidative reactions cannot be quenched.
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| 35. |
- Ljungdahl, Jonas, et al.
(författare)
-
Transverse anisotropy of compressive failure in European oak : A digital speckle photography study
- 2006
-
Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 60:2, s. 190-195
-
Tidskriftsartikel (refereegranskat)abstract
- The mechanical behaviour of European oak (Quercus robur L.) was studied in radial and tangential compression. Young's modulus and the yield strength were approximately 1.7- and 1.6-fold higher, respectively, in the radial direction. Strain fields were determined by digital speckle photography (DSP). Strains and the effective Poisson ratio could be determined separately in earlywood and latewood during deformation and failure events. In radial compression, strain data showed that rays contributed significantly to the high modulus. In addition, multiseriate ray microbuckling was observed to control yield strength. The microbuckling was localised in the low- density earlywood. In tangential compression, yield strength was controlled by vessel collapse in the low- density regions of the latewood. The strain field data provide direct evidence that the rays are the main microstructural factor controlling transverse anisotropy in European oak.
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| 36. |
- Ljungdahl, Jonas, et al.
(författare)
-
Transverse mechanical behaviour and moisture adsorption of waterlogged archaeological wood from the Vasa ship
- 2007
-
Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 61:3, s. 279-284
-
Tidskriftsartikel (refereegranskat)abstract
- Damage on the hull of the 17th century Swedish warship Vasa has been observed recently. Damage in the form of indentations in the wood is caused by high compressive loads from the support structure. In the process of developing an improved support structure, radial mechanical properties and the deformation mechanisms of Vasa oak are particularly important. Causes of differences in PEG content and oak degradation are also of interest. The radial modulus and compressive strength of Vasa oak are 50% lower than for recent oak. Furthermore, a significant change in failure mechanism is observed. More brittle separation fracture of the rays of Vasa oak is observed compared to the continuous folds of rays in recent oak. Tangential stiffness and strength are also 30% and 50% lower, respectively. Comparably small differences in moisture absorption between PEG-extracted Vasa oak and recent oak indicate a low extent of degradation of the Vasa oak.
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| 37. |
- Modén, Carl S., 1979-, et al.
(författare)
-
Elastic deformation mechanisms of softwoods in radial tension : Cell wall bending or stretching?
- 2008
-
Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 62:5, s. 562-568
-
Tidskriftsartikel (refereegranskat)abstract
- Radial softwood modulus ER is typically twice as high as the tangential modulus ET. The reason for this is unclear, although cell geometry is likely to contribute. The established hexagonal honeycomb model for prediction of ER is based on a cell wall bending mechanism only. If cell wall stretching also takes place, the dependence of ER on relative density will be different. If experimental data for ER as a function of relative density show deviations from cell wall bending predictions, this may indicate the presence of cell wall stretching. A SilviScan apparatus is used to measure density distribution. A procedure by means of digital speckle photography is then developed for measurements of local ER within the annual rings of spruce. Comparison is made between experimental data and the two expected density dependencies from cell wall bending and from stretching. The hypothesis of cell wall stretching as a contributing mechanism is supported based on the observed linear dependence of ER over a wide density range.
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| 38. |
- Nagy, M., et al.
(författare)
-
Catalytic hydrogenolysis of ethanol organosolv lignin
- 2009
-
Ingår i: Holzforschung. - 1437-434X .- 0018-3830. ; 63:5, s. 513-520
-
Tidskriftsartikel (refereegranskat)abstract
- The production of ethanol based on lignocellulosic materials will bring about the coproduction of significant amounts of under-utilized lignin. This study examines the potential of conventional heterogeneous and novel homogeneous catalysts for the selective cleavage of the aryl-O-aryl and aryl-O-aliphatic linkages of ethanol organosolv lignin to convert it from a low grade fuel to potential fuel precursors or other value added chemicals. The development of hydrogenolysis conditions that effectively increase the solubility of lignin were initially examined with Ru(Cl)(2)(PPh3)(3) and demonstrated the ability to decrease the molecular weight and enhance the solubility of the lignin polymer. Later studies examined several heterogeneous and homogeneous hydrogenation catalysts at optimized reaction conditions resulting in 96.4% solubility with Ru(Cl)(2)(PPh3)(3), increase in H/C ratio with Raney-Ni, Pt/C and extensive monomer formation with NaBH4/I-2. The changes in molecular structure of lignin were followed by size exclusion chromatography, qualitative and quantitative NMR spectroscopy and elemental analysis. These studies demonstrated that aryl-O-aryl and aryl-O-aliphatic linkages could be cleaved and the hydrogenated lignin had a decrease in oxygen functionality and the formation of products with lower oxygen content.
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| 39. |
- Nilsson, David, et al.
(författare)
-
Pine and spruce roundwood species classification using multivariate image analysis on bark
- 2005
-
Ingår i: Holzforschung. - Berlin : Walter de Gruyter. - 0018-3830 .- 1437-434X. ; 59:6, s. 689-695
-
Tidskriftsartikel (refereegranskat)abstract
- Wood discs from 67 pine and 79 spruce logs were collected from a forest clearing. Three different 24-bit red-green-blue (RGB) images were acquired from the radial surface of each disc. The first image contained bark, the second image was a mixture of bark and wood surface, and the third image consisted only of wood surface. The image texture was compressed into vectors of Fourier-transformed wavelet coefficients. These were assembled in matrices and analysed by principal component analysis (PCA) and partial least-squares projections to latent structures (PLS). Classification using Fourier-transformed wavelet scales showed that the wood species could be predicted with 90% accuracy. A thorough examination of this classification showed that the predicting power of these models was mostly due to wavelet scales that represented the mean value of each colour channel. The prediction accuracy that could be obtained from coefficients representing image texture was generally low. The use of grey-level co-occurrence matrices prior to the wavelet transformation showed, however, that it is possible to classify the wood species of pine and spruce with an accuracy approaching 100%.
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| 40. |
- Nocanda, Xolani, et al.
(författare)
-
Cross polarisation/magic angle spinning C-13-NMR spectroscopic studies of cellulose structural changes in hardwood dissolving pulp process
- 2007
-
Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 61:6, s. 675-679
-
Tidskriftsartikel (refereegranskat)abstract
- Cross polarisation/magic angle spinning C-13 NMR spectroscopy has been used to study structural changes in cellulose induced by the dissolving pulp process. The cellulose structure in several dissolving pulps was investigated for commercial and laboratory cooked Eucalyptus 92 alpha and 96 alpha. The average lateral dimension, or average thickness, of the cellulose fibril aggregates is related to the amount of surface area exposed and could be one controlling factor for the chemical reactivity of commercial dissolving pulps during modification reactions. The thickness of the cellulose fibril aggregates governs the amount of surface area present in the fibre wall, and cellulose surface material constitutes the part of the cellulose that is directly accessible to reagents. In all sample series investigated, the raw pulp was found to be less aggregated than the corresponding bleached final pulp. Furthermore, an irreversible increase in fibril aggregate width was observed on free drying for both laboratory cooked and commercial pulps. Upon rewetting with water, the freely dried 96 alpha pulp was found to be more aggregated than the freely dried 92 alpha pulp, although sugar analysis showed very similar carbohydrate compositions. As indicated by the molecular mass distribution, the commercial 92 alpha pulp contained larger amounts of degraded cellulose; this may be a plausible explanation for the different behaviour of the 92 alpha and 96 alpha pulps during free drying.
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| 41. |
- Nordstierna, Lars, et al.
(författare)
-
Towards novel wood-based materials : chemical bonds between lignin-like model molecules and poly(furfuryl alcohol) studied by NMR
- 2008
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 62:6, s. 709-713
-
Tidskriftsartikel (refereegranskat)abstract
- Wood modification with furfuryl alcohol is a non-toxic alternative to conventional preservation treatments. A process in which furfuryl alcohol polymerises in situ was previously proposed for chemical modification of wood. In the present work, liquid model systems were investigated using compounds that resemble repeating units of lignin to verify whether chemical bonds form between the furfuryl alcohol polymer and wood. Using different NMR spectroscopic techniques we confirmed that these model compounds do form covalent bonds with the polymerising polymer. The results indicate that the furan polymer grafts to lignin, supporting observations in similar studies performed with genuine wood materials.
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| 42. |
- Pantze, Anna, et al.
(författare)
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Esterification of carboxylic acids on cellulosic material : solid state reactions
- 2008
-
Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 62:2, s. 136-141
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Tidskriftsartikel (refereegranskat)abstract
- In the present work, the formation of ester linkages in cellulosic materials during drying and heating was addressed. The results indicated that direct ester formation, without anhydride intermediate, occurs between carboxylic acids of suitable structure and cellulosic hydroxyls at 180 degrees C, even after reaction times as short as 5 min. The 2(R)-hydroxybutyric acid is most effective in ester formation, followed by 2-ketobutyric acid and 3-hydroxybutyric acid. Hexanoic acid is less effective and veratric acid produces no esters at all. At lower temperatures, 2-ketobutyric acid is the most reactive compound. One conclusion is that a hydroxyl or keto group in alpha position of the carboxylic acids favours ester formation. Another finding is that three pyrrolidine structures are produced after esterification and aminolysis of 2-ketobutyric acid. One of the structures indicates that 2-ketobutyric acid is reactive in two positions and could therefore be a potential cross-linker. A critical parameter for ester formation is pH, and the results indicate that pH < 2 strongly favours esterification, whereas almost no esters are produced at pH > 5-6. All experiments were performed in a solid-state model system (on cellulosic filter paper) with low moisture content. Esterification of five carboxylic acids was studied. Samples were heated constantly at 180 degrees C for 5 min or gradually from 22 degrees C to 180 degrees C over periods ranging from 5 to 45 min. Quantitative analysis of ester formation between the monocarboxylic acids and the hydroxyl groups of cellulose was performed by means of aminolysis and gas chromatography.
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| 43. |
- Raberg, U., et al.
(författare)
-
Detection and species discrimination using rDNA T-RFLP for identification of wood decay fungi
- 2005
-
Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 59:6, s. 696-702
-
Tidskriftsartikel (refereegranskat)abstract
- In the present work PCR technology was used as a tool to detect the early stages of wood decay and was compared with microscopic evaluation. The wood decay fungi Postia placenta and Coniophora puteana were detectable in interior wood samples by terminal restriction fragment length polymorphism (T-RFLP) after 2 weeks of incubation with monocultures, while microscopic detection of hyphae was not possible until after 7 weeks. A potential problem when fungal communities are studied with T-RFLPs of rDNA is that intra-specific variation complicates data analysis. In this work, we show that intra-specific sequence variation in the internal transcribed spacer of the rDNA in Coniophora puteana allows T-RFLP identification of this species. This is due to intra-specific variations in fragment length, in combination with the absence of point mutations in the selected restriction sites.
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| 44. |
- Raberg, Ulrika, et al.
(författare)
-
External and internal fungal flora of pine sapwood (Pinus sylvestris L.) specimens in above-ground field tests at six different sites in south-west Germany
- 2007
-
Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 61:1, s. 104-111
-
Tidskriftsartikel (refereegranskat)abstract
- The occurrence of fungal species on pine sapwood samples obtained from an above-ground field test study was analysed by terminal restriction fragment length polymorphism (T-RFLP), cloning, and sequencing. Samples were taken from eight double-layer set-ups that were exposed to the environment at six different locations in south-west Germany. The occurrence of fungal species was correlated with decay intensity and rot types on one hand, and characteristics of the test sites, such as precipitation, average temperature and height above sea level on the other hand. In total, 62 different fungal species were found based on T-RFLP cloning and sequencing. Of the 39 species that were found four or more times, 30 were ascomycetes, five were basidiomycetes, and four could not be classified. The most common fungus found in this study was Coniochaeta ligniaria ((Grev.) Cooke), a soft rot fungus that occurred in 87 of 152 samples (57%). No single factor at the test sites seemed to be decisive for the abundance of fungal species or decay intensity. Within the first years of this study, soft rot fungi was found more frequently in pine sapwood specimens than basidiomycetes.
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| 45. |
- Rencoret, Jorge, et al.
(författare)
-
Structural characterization of milled wood lignins from different eucalypt species
- 2008
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 62:5, s. 514-526
-
Tidskriftsartikel (refereegranskat)abstract
- The chemical structure of milled-wood lignins from Eucalyptus globulus, E. nitens, E. maidenii, E. grandis, and E. dunnii was investigated. The lignins were characterized by analytical pyrolysis, thioacidolysis, and 2D-NMR that confirmed the predominance of syringyl over guaiacyl units and only showed traces of p-hydroxyphenyl units. E. globulus lignin had the highest syringyl content. The heteronuclear single quantum correlation (HSQC) NMR spectra yielded information about relative abundances of inter-unit linkages in the whole polymer. All the lignins showed a predominance of beta-O-4' ether linkages (66-72% of total side-chains), followed by beta-beta' resinol-type linkages (16-19%) and lower amounts of beta-5' phenylcoumarin-type (3-7%) and beta-1' spirodienone-type linkages (1-4%). The analysis of desulfurated thioacidolysis dimers provided additional information on the relative abundances of the various carbon-carbon and diaryl ether bonds, and the type of units ( syringyl or guaiacyl) involved in each of the above linkage types. Interestingly, 93-94% of the total beta-beta' dimers included two syringyl units indicating that most of the beta-beta' substructures identified in the HSQC spectra were of the syringaresinol type. Moreover, three isomers of a major trimeric compound were found which were tentatively identified as arising from a beta-beta' syringaresinol substructure attached to a guaiacyl unit through a 4-O-5' linkage.
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| 46. |
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| 47. |
- Salmen, Lennart, et al.
(författare)
-
Cell wall features with regard to mechanical performance. A review. : COST Action E35 2004-2008 : Wood machining - Micromechanics and fracture
- 2009
-
Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 63:2, s. 121-129
-
Tidskriftsartikel (refereegranskat)abstract
- The mechanical performance of wood and wood products is highly dependent on the structural arrangement and properties of the polymers within the fibre cell wall. To improve utilisation and manufacture of wood materials, there is an increasing need for a more detailed knowledge regarding structure/property relations at the micro- or nanostructural level. In this article, recent developments regarding our understanding of the wood cell wall structure and its mechanical performance are summarised. The new results are interpreted in relation to property performances of wood fibres and wood tissues. Suggestions are made for future requirements for research in this field. © 2009 by Walter de Gruyter.
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| 48. |
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| 49. |
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| 50. |
- Sjödin, Johan, et al.
(författare)
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An experimental study of the effects of moisture variations and gradients in the joint area in steel-timber dowel joints
- 2008
-
Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 62:2, s. 243-247
-
Tidskriftsartikel (refereegranskat)abstract
- This experimental study examines the influence of moisture variations on the load-bearing capacity of steeltimber dowel joints. The glulam specimens used to manufacture the joints were first exposed to controlled climate changes. After being stored in the climate chambers, holes were drilled and dowels were inserted. Then, the joints were loaded to failure. The main aim of this study was to investigate how and to what extent moisture variations and gradients in the joint area affects the load-bearing capacity in tension parallel to the grain. The load-bearing capacity was found to be reduced under these conditions when compared to reference joints. Moreover, the brittleness of the joints increased with the time the joints had been exposed to drying. Moistureinduced stresses and cracks in the joint area were found to be a possible explanation of the results. A similar interpretation was given in other studies where other structural timber elements have been studied. This raises an important question of how such moisture effects should be considered in design codes. One possibility is to include the influence of moisture-induced stresses in the k_mod factor used in Eurocode 5. Another way could be to consider this type of moisture effect as an equivalent mechanical load case.
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