| 1. |
- Ahmed, Sheikh Ali, et al.
(författare)
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Uneven distribution of preservative in kiln-dried sapwood lumber of Scots pine : Impact of wood structure and resin allocation
- 2012
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Ingår i: Holzforschung. - : Walter de Gruyter. - 0018-3830 .- 1437-434X. ; 66:2, s. 251-258
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Tidskriftsartikel (refereegranskat)abstract
- Scots pine (Pinus sylvestris L.) sapwood lumber was collected after kiln drying and preservative treatment with Celcure AC 800 (a copper-amine wood preservative). Distribution of the preservative throughout the lumber was visually examined. Not all, but some samples showed specific localized areas without any preservative distribution throughout their entire length. Those samples were assessed further for anatomical properties, specifically in impregnated and unimpregnated areas. Additional study was conducted on the morphological nature and redistribution of lipophilic extractives using three different histochemical staining methods. Intrinsic wood properties – especially the frequency of axial resin canals and the percentage of canals blocked – were found to be responsible for the irregular distribution of the preservative. Furthermore, the inability to create continuous and frequent interstitial spaces due to the collapse of thin-walled ray cells throughout the lumber resulted in un-even distribution of preservatives. Staining techniques were useful to localize places with more or less abundance of extractives (e.g., fats) in impregnated and unimpregnated wood, which varied considerably. Histochemical observations revealed information pertaining to the kiln dry specific distribution and redistribution of extractives between the areas. Moreover, resin reallocation and modification in ray parenchyma and resin canals induced by kiln drying would be another reason for the impregnation anomalies.
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| 2. |
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| 3. |
- Almlöf Ambjörnsson, Heléne, 1968-, et al.
(författare)
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Enzyme pretreatment of dissolving pulp as a way to improve the following dissolution in NaOH/ZnO
- 2014
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Ingår i: Holzforschung. - : Walter de Gruyter. - 0018-3830 .- 1437-434X. ; 68:4, s. 385-391
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Tidskriftsartikel (refereegranskat)abstract
- The dissolution of a softwood dissolving pulp in a NaOH/ZnO system was improved by means of a three-stage pretreatment with an initial xylanase treatment, followed by an alkaline extraction, and finally an endoglucanase stage. The solubility of the pulp increased from 29% to 81%, although the crystallinity and the specific surface area of the pulp did not change during the enzymatic treatment.
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| 4. |
- Almlöf, Heléne, 1968-, et al.
(författare)
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The influence of extended mercerization on some properties of carboxymethyl cellulose (CMC)
- 2012
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 66, s. 21-27
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Tidskriftsartikel (refereegranskat)abstract
- Carboxymethyl cellulose (CMC) is produced commercially in a two stage process consisting of a mercerization stage in which the pulp is treated with alkali in a water alcohol solution and a second etherification stage whereby monochloro-acetic acid is added to the pulp slurry. In this study, the influence of the conditions of an extended mercerization stage was evaluated on the etherification stage concerning the degree of substitution (DS) and the filterability of the resulting CMC. The parameters studied were: (1) the ratio of cellulose I and cellulose II in the original pulp, (2) the concentration of alkali, (3) the temperature and (4) the retention time in the mercerization stage. The DS results indicate that the NaOH concentration in the mercerization stage is the most important among the parameters studied. When the NaOH concentration in the mercerization stage was high (27.5%), cellulose II showed a lower reactivity than cellulose I with respect to the DS obtained in the resulting CMC. The results from the filtration ability of CMC water solutions are interpreted that the amount of cellulose II in the original pulp and the temperature has a negative influence, while the NaOH concentration in the mercerization stage has a positive influence on the filtration ability. Retention time between 1 h–48 h in the mercerization stage had no effect on the DS or the filtration value. The filtration ability was assumed to be highly influenced by the presence of poorly reacted cellulose segments. The CMC samples with the lowest filtration ability at a given DS can be assumed to have the highest degree of unevenly substituted segments.
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| 5. |
- Anugwom, Ikenna, et al.
(författare)
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Treating birch wood with a switchable 1,8-diazabicyclo-[5.4.0]-undec-7-ene-glycerol carbonate ionic liquid
- 2012
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 66:7, s. 809-815
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Tidskriftsartikel (refereegranskat)abstract
- The suitability of a new switchable ionic liquid (SIL) has been investigated as a solvent for fractionation of lignocellulosic materials. SIL was prepared from inexpensive chemicals, e. g., glycerol, CO2, and 1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU). Fresh Nordic birch wood (B. pendula) was treated with the SIL for a time period of 1-5 days at 100 degrees C and under atmospheric pressure. Upon SIL treatment, at best, 57 % of the hemicelluloses were dissolved and 50 % of lignins were dissolved from the native birch. The slightly fibrillated SIL treated chips contained about 55 % cellulose. Up to 76 % of the recovered species removed from the spent SIL liquor was originating from hemicelluloses, mainly from xylan. The spent SILs were reused for fresh wood dissolution in four consecutive cycles and each time the wood dissolution efficiency was similar. SILs could offer affordable (easy-to-synthesize) solvent systems for partial elimination of hemicelluloses and lignin from wood. SILs can also be prepared in-situ and on-site.
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| 6. |
- Areskogh, Dimitri, et al.
(författare)
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Oxidative polymerisation of models for phenolic lignin end-groups by laccase
- 2010
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 64:1, s. 21-34
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Tidskriftsartikel (refereegranskat)abstract
- The redox enzyme laccase can lead to cross-linking of lignin molecules by oxidising phenolic end groups to resonance-stabilised radicals that can undergo radical coupling to form covalent bonds. This property has potential for many technical applications. However, laccase treatment can also lead to degradation. Experiments were performed with two laccases of different oxidation potential and pH and temperature optima. The predominant reaction following laccase oxidation is the formation of 5-5' and 4-O-5' bonds. If the 5-position is blocked, other reactions occur, including coupling of the 1-position and oxidation of the a-position, which aggravates cross-linking of different lignin molecules. The product profile generated by the two laccases is somewhat different, mainly because of the different pH rather than differences in enzyme activity. Reaction mechanisms and the technical and biological significance of the results are discussed.
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| 7. |
- Bader, Thomas K., et al.
(författare)
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Changes in microstructure and stiffness of Scots pine (Pinus sylvestris L) sapwood degraded by Gloeophyllum trabeum and Trametes versicolor Part II : Anisotropic stiffness properties
- 2012
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 66:2, s. 199-206
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Tidskriftsartikel (refereegranskat)abstract
- Fungal decay considerably affects the macroscopic mechanical properties of wood as a result of modifications and degradations in its microscopic structure. While effects on mechanical properties related to the stem direction are fairly well understood, effects on radial and tangential directions (transverse properties) are less well investigated. In the present study, changes of longitudinal elastic moduli and stiffness data in all anatomical directions of Scots pine (Pinus sylvestris) sapwood which was degraded by Gloeophyllum trabeum (brown rot) and Trametes versicolor (white rot) for up to 28 weeks have been investigated. Transverse properties were found to be much more deteriorated than the longitudinal ones. This is because of the degradation of the polymer matrix between the cellulose microfibrils, which has a strong effect on transverse stiffness. Longitudinal stiffness, on the other hand, is mainly governed by cellulose microfibrils, which are more stable agains fungal decay. G. trabeum (more active in earlywood) strongly weakens radial stiffness, whereas T. versicolor (more active in latewood) strongly reduces tangential stiffness. The data in terms of radial and tangential stiffnesses, as well as the corresponding anisotropy ratios, seem to be suitable as durability indicators of wood and even allow conclusions to be made on the degradation mechanisms of fungi.
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| 8. |
- Bader, Thomas K., et al.
(författare)
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Microstructure and stiffness of Scots pine (Pinus sylvestris L) sapwood degraded by Gloeophyllum trabeum and Trametes versicolor Part I : Changes in chemical composition, density and equilibrium moisture content
- 2012
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 66:2, s. 191-198
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Tidskriftsartikel (refereegranskat)abstract
- Fungal degradation alters the microstructure of wood and its physical and chemical properties are also changed. While these changes are well investigated as a function of mass loss, mass density loss and changes in equilibrium moisture content are not well elucidated. The physical and chemical alterations are crucial when linking microstructural characteristics with macroscopic mechanical properties. In the present article, a consistent set of physical, chemical and mechanical characteristics is presented, which were measured on the same sample before and after fungal degradation. In the first part of this two-part contribution, elucidating microstructure/stiffness-relationships of degraded wood, changes in physical and chemical data are presented, which were collected from specimens of Scots pine (Pinus sylvestris) sapwood degraded by Gloeophyllum trabeum (brown rot) and Trametes versicolor (white rot) for up to 28 weeks degradation time. A comparison of mass loss with corresponding mass density loss demonstrated that mass loss entails two effects: firstly, a decrease in sample size (more pronounced for G. trabeum), and secondly, a decrease of mass density within the sample (more pronounced for T. versicolor). These two concurrent effects are interrelated with sample size and shape. Hemicelluloses and cellulose are degraded by G. trabeum, while T. versicolor was additionally able to degrade lignin. In particular because of the breakdown of hemicelluloses and paracrystalline parts of cellulose, the equilibrium moisture content of degraded samples is lower than that in the initial state.
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| 9. |
- Bjurhager, Ingela, et al.
(författare)
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Mechanical performance of yew (Taxus baccata L.) from a longbow perspective
- 2013
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 67:7, s. 763-770
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Tidskriftsartikel (refereegranskat)abstract
- Yew (Taxus baccata L.) longbow was the preferred weapon in the Middle Ages until the emergence of guns. In this study, the tensile, compression, and bending properties of yew were investigated. The advantage of yew over the other species in the study was also confirmed by a simple beam model. The superior toughness of yew has the effect that a yew longbow has a higher range compared with bows made from other species. Unexpectedly, the mechanical performance of a bow made from yew is influenced by the juvenile-to-mature wood ratio rather than by the heartwood-to-sapwood ratio. A yew bow is predicted to have maximized performance at a juvenile wood content of 30-50%, and located at the concave side (the compressive side facing the bowyer). Here, the stiffness and yield stress in compression should be as high as possible.
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| 10. |
- Bjurhager, Ingela, et al.
(författare)
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Towards improved understanding of PEG-impregnated waterlogged archaeological wood : A model study on recent oak
- 2010
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 64:2, s. 243-250
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Tidskriftsartikel (refereegranskat)abstract
- To prevent deformation and cracking of waterlogged archaeological wood, polyethylene glycol (PEG) as a bulk impregnation agent is commonly applied. PEG maintains the wood in a swollen state during drying. However, swelling of wood can reduce its mechanical properties. In this study, the cellular structure of oak and cell wall swelling was characterized by scanning electron microscopy (SEM) of transverse cross-sections, and the microfibril angle of oak fibers was determined by wide angle X-ray scattering (WAXS). Samples of recent European oak (Quercus robur L) impregnated with PEG (molecular weight of 600) were tested in axial tension and radial compression. Mechanical tests showed that axial tensile modulus and strength were only slightly affected by PEG, whereas radial compressive modulus and yield strength were reduced by up to 50%. This behavior can be explained by the microstructure and deformation mechanisms of the material. Microfibril angles in tensile test samples were close to zero. This implies tensile loading of cellulose microfibrils within the fiber cell walls without almost any shear in the adjacent amorphous matrix. These results are important because they can help separate the impact of PEG on mechanical properties from that of chemical degradation in archaeological artifacts, which display only small to moderate biological degradation.
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| 11. |
- Brodin, Ida, 1982-, et al.
(författare)
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Oxidative stabilisation of kraft lignin for carbon fibre production
- 2012
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Ingår i: Holzforschung. - : Walter de Gruyter. - 0018-3830 .- 1437-434X. ; 66:2, s. 141-147
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Tidskriftsartikel (refereegranskat)abstract
- With the aim of investigating kraft lignin as a raw material for carbon fibre production, different lignins have been stabilised in air at conditions varied according to a full factorial experimental design. The lignins under examination were purified kraft lignin powders originating from birch, spruce/pine and Eucalyptus globules, as well as lignin fibres originating from birch with 5% poly(ethylene oxide) (PEO) added as a plasticiser. The influence of temperature, time and heating rate on yield and glass-transition temperature (Tg) was investigated. The highest yield was achieved after stabilisation at 280C during 2 h with a heating rate of 0.2C min-1. The Tg of all lignin powders was increased when stabilisation occurred under harsher conditions. X-ray photoelectron spectroscopy analysis (XPS) of both the outer surface and the cleaved cross-section of individual lignin/PEO fibres showed a clear gradient in the degree of chemical modification, with the major change occurring on the surface resulting in the appearance of a skin-core structure after stabilisation. The behaviour of the lignin fibres during stabilisation is similar to that of pitch-based fibres, indicating good possibilities for lignin as raw material for carbon fibre production.
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| 12. |
- Bryne, Lars-Elof, et al.
(författare)
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Ageing of modified wood : Part 2: Determination of surface composition of acetylated, furfurylated, and thermally modified wood by XPS and ToF-SIMS
- 2010
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 64:3, s. 305-313
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Tidskriftsartikel (refereegranskat)abstract
- The main objective of this work was to study the chemical composition of surfaces and ageing effects on acetylated pine (Pinus sylvestris), heat treated spruce (Picea abies), and furfurylated radiata pine (Pinus radiata) in comparison to unmodified wood. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were the instruments of choice. Observation with a low-vacuum scanning electron microscope (LV-SEM) complemented the study. The spectroscopic information was also linked to a parallel wettability study on matched wood samples by the Wilhelmy method. The results show that XPS and ToF-SIMS are two powerful tools that in combination give complementary information, both quantitative and qualitative, and are well suited for observation of the ageing process of different wood surfaces. The hydrophobization process as a result of migration of extractives during ageing was well quantified by the XPS measurements and the results correlated well with wetting results. Several specific hydrophobic substances could be identified by ToF-SIMS measurements.
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| 13. |
- Bryne, Lars-Elof, et al.
(författare)
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Ageing of modified wood : Part 1: Wetting properties of acetylated, furfurylated, and thermally modified
- 2010
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 64:3, s. 295-304
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Tidskriftsartikel (refereegranskat)abstract
- The main objective of this work was to apply contact angle analysis to predict work of adhesion (W-a) between some modified wood materials and certain thermoplastics and adhesives. Wetting properties, i.e., contact angles, were measured by the Wilhelmy method on both freshly prepared and aged veneer samples of unmodified and acetylated Scots pine, furfurylated radiata pine, and heat treated Norway spruce. The sessile drop method was used to measure contact angles on a phenol resorcinol formaldehyde, an emulsion polymer isocyanate, and a one-component polyurethane adhesive. Contact angle data were also collected from the literature on polyethylene, polyvinyl chloride, polymethyl methacrylate, polystyrene, and Nylon 6. Contact angle analysis based on the Chang-Qin-Chen model was then applied to determine so-called acid-base interaction parameters and W-a between the wood samples and the selected thermoplastics and adhesives. Results show that the ageing process led to an increased hydrophobic character of unmodified, heat treated, and furfurylated wood samples. The freshly prepared acetylated wood samples had a pronounced hydrophobic character which remained approximately constant after ageing. The predicted W-a between the wood and the adhesives was considerably higher than that between the wood and the thermoplastics. Furthermore, the predicted W-a between the acetylated wood and both the thermoplastics and water was approximately unchanged when comparing the fresh and aged samples. In contrast, the ageing of all other wood samples resulted in a dramatic decrease of the wood-water W-a and a moderate decrease of the wood-thermoplastics W-a. The wood-adhesives W-a, however, was unchanged for the unmodified and furfurylated wood when comparing the fresh and aged samples and even increased for heat treated and acetylated wood samples.
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| 14. |
- Chunilall, V., et al.
(författare)
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A CP/MAS 13C-NMR study of cellulose fibril aggregation in eucalyptus dissolving pulps during drying and the correlation between aggregate dimensions and chemical reactivity
- 2010
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 64:6, s. 693-698
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Tidskriftsartikel (refereegranskat)abstract
- Changes in supramolecular properties of cellulose I, namely its lateral fibril aggregate dimension (LFAD), in bleached hardwood acid bisulphite pulp during drying was studied using cross-polarization/magic angle spinning carbon-13 nuclear magnetic resonance (CP/MAS 13C-NMR) in combination with spectral fitting. A significant change in aggregate dimensions was noticed when each of the pulp grades were oven dried. The effect of drying was further investigated with pulp samples subjected to different drying methods. A comparison of a harsh oven drying, mild and rapid air drying, and a very mild and slow condition drying showed that the LFAD of the material decreases in the following order: oven drying > air drying > condition drying. The correlation between the total extractable material S10 (%) and LFAD and also the LFAD increment (ΔLFAD in %) are presented and shown to be intimately related. This means that the method of drying influences the size of the fibril aggregate dimensions and depends on the presence of extractable material within the fibre cell wall. Reactivity studies were carried out based on the acetylation of cotton linters and commercial 96α pulp. Results indicate that the initial reaction rate is proportional to the specific surface area of the two cellulose pulp samples. Accordingly, the specific surface area is directly related to initial reactivity of the performed acetylation. We demonstrated that it is possible to control the LFAD and hence specific surface area in laboratory-produced pulps 91α, 92α, and 96α by the drying method. Thus controlling LFAD can probably be one viable route for controlling the initial reactivity of dissolving pulp towards acetylation.
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| 15. |
- Dedic, Dina, et al.
(författare)
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Analysis of lignin and extractives in the oak wood of the 17th century warship Vasa
- 2014
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 68:4, s. 419-425
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Tidskriftsartikel (refereegranskat)abstract
- The wood in the 17th century Swedish warship Vasa is weak. A depolymerization of the wood's cellulose has been linked to the weakening, but the chemical mechanisms are yet unclear. The objective of this study was to analyze the lignin and tannin moieties of the wood to clarify whether the depolymerization of cellulose via ongoing oxidative mechanisms is indeed the main reason for weakening the wood in the Vasa. Lignin was analyzed by solid-state nuclear magnetic resonance [cross-polarization/magic-angle spinning (CP/MAS) C-13 NMR] and by means of wet chemical degradation (thioacidolysis) followed by gas chromatography-mass spectrometry (GC-MS) of the products. No differences could be observed between the Vasa samples and the reference samples that could have been ascribed to extensive lignin degradation. Wood extracts (tannins) were analyzed by matrix- assisted laser desorption ionization (MALDI) combined with time-of-flight (TOF) MS and C-13 NMR spectroscopy. The wood of the Vasa contained no discernible amounts of tannins, whereas still-waterlogged Vasa wood contained ellagic acid and traces of castalagin/vescalagin and grandinin. The results indicate that the condition of lignin in the Vasa wood is similar to fresh oak and that potentially harmful tannins are not present in high amounts. Thus, oxidative degradation mechanisms are not supported as a primary route to cellulose depolymerization.
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| 16. |
- Doliška, A., et al.
(författare)
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Antithrombotic properties of sulfated wood-derived galactoglucomannans
- 2012
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 66:2, s. 149-154
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Tidskriftsartikel (refereegranskat)abstract
- Galactoglucomannans (GGMs) are water-soluble polysaccharides released and accumulated in process waters in the production of thermomechanical pulp. The general trend in the forestry industry is moving towards bio-refineries, for example utilizing these hemicelluloses as bioactive substances. At present, there is no industrial use of wood-derived mannans. In this study, GGMs extracted from thermomechanical pulp, as well as further carboxymethyl-ated galactoglucomannans (CM-GGMs), were sulfated to increase their antithrombotic properties. The products were characterized with Fourier transform infrared spectroscopy, nuclear magnetic resonance and capillary electrophoresis. The carbohydrate composition and sulfur amounts were determined. The products' total charges were determined by polyelectrolyte titrations and their antithrombotic effect was measured based on the activated partial thromboplastin time. The results showed a significant increase in the antithrombotic effect of the sulfated galactoglucomannans from spruce wood and thus a potential new use for wood-derived mannans.
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| 17. |
- Du, Xueyu, et al.
(författare)
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Improvement of kraft pulp bleaching by treatments with laccase, urea, and refining
- 2013
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 67:6, s. 651-658
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Tidskriftsartikel (refereegranskat)abstract
- Unbleached Eucalyptus kraft pulps were treated by three methods and the bleaching effects have been evaluated. The treatments were performed by a laccase mediator system (LMS), refining (R), and urea (U) alone and in combination of these methods. The bleached pulps were characterized in terms of κ number, hexenuronic acid content, brightness, and viscosity. In addition, the lignin-carbohydrate complexes (LCCs) were fractionated and characterized with regard to the fractionation yield, lignin content, and carbohydrate composition. Moreover, the 1 H nuclear magnetic resonance spectra were recorded and the thioacidolysis-gas chromatography and thioacidolysis-size exclusion chromatography analyses were performed. The LMS treatment resulted mainly in a slightly better delignification as manifested by a κ number (K no.) reduction of 0.8 units. The effects of the U treatment included delignification (1.4 κ units), hexenuronic acid removal (3 μ mol g-1), and improved pulp brightness (3.4 ISO units). The R treatment darkened the pulp (3 ISO units), whereas the bleaching of the R-pulp by subsequent LMS or U treatment enhanced the brightness (0.5 unit more) or delignification (0.3 unit more). The residual lignin in the pulp samples was present mainly as xylan-lignin. The Klason lignin content from the xylan lignin fraction decreased as the degree of delignification increased. The pulp darkening followed by the R treatment was interpreted as the result of the formation of condensed lignin structures, but these condensed lignins were substantially removed by the subsequent LMS or U treatment.
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| 18. |
- Dvinskikh, Sergey V., et al.
(författare)
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A multinuclear magnetic resonance imaging (MRI) study of wood with adsorbed water : Estimating bound water concentration and local wood density
- 2011
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 65:1, s. 103-107
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between moisture and the macromolecular wood tissue is of critical importance to wood properties. In this context, magnetic resonance imaging (MRI) is very promising as this method could deliver molecular information on the submillimeter scale (i.e., along concentration gradients) about both free and adsorbed water and the cell wall polymers. In the present study, it is demonstrated for the first time that wood containing adsorbed heavy water ((H2O)-H-2) can be studied by MRI based on separated images due to water (H-2 MRI) and cell wall polymers (H-1 MRI). Data confirm that in specimens equilibrated at controlled humidity there is a direct correlation between bound water content and relative density of the polymers in wood tissue; there is a strong variation across annual rings.
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| 19. |
- Engelund, Emil Tang, et al.
(författare)
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Tensile creep and recovery of Norway spruce influenced by temperature and moisture
- 2012
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 66:8, s. 959-965
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Tidskriftsartikel (refereegranskat)abstract
- The time-dependent mechanical behaviour (TDMB) of wood is important when using the material for structural purposes. Recently, a new method for predicting the TDMB by numerical modelling was established based on the assumption that TDMB is caused by the sliding of the microfibrils past each other. In this study, the TDMB is examined via creep experiments on small specimens of Norway spruce latewood. The results of these are compared with results from numerical modelling. The experiments include results at two levels of moisture content and three levels of temperature, enabling an investigation of these two climatic factors on TDMB of wood. It was found that the mechanical response of wood tissue is the sum of responses from both tracheids and middle lamella, with only the previous being reversible. The effect of moisture and temperature differed in that the latter affected the elastic and time-dependent responses equally. Moisture, on the other hand, reduced both the elastic properties and the activation energy barrier for sliding of the microfibrils, but furthermore changed the microfibril angle of the sample as a result of swelling. Hereby, moisture had a larger effect on the time-dependent response than the elastic. All of these effects were predicted by numerical modelling.
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| 20. |
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| 21. |
- Fernando, Dinesh, et al.
(författare)
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Characterization of fiber development in high- and low-consistency refining of primary mechanical pulp
- 2013
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 67, s. 735-745
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Tidskriftsartikel (refereegranskat)abstract
- Primary refined softwood was subjected to highconsistency (HC) or low-consistency (LC) secondary refining, and the nature of the development of the internal and external fiber microstructure and ultrastructure has been compared. The primary refining of mixed softwood as a raw material was performed in pilot scale by the advanced thermomechanical pulp process. The study was aiming at the comparative characterization of LC and HC pulps at the fiber level when produced with similar and well-characterized handsheet properties. The formerly described Simons ’ staining method was applied. A significant degree of fiber wall delamination/internal fibrillation (D/IF) was observed during both LC and HC refining. Both the energy input and the refining consistency had a significant impact on elevating the degree of fiber wall D/IF. The statistical evaluation of internal fiber development indicated that the fiber populations in LC- and HC-refined pulps had a similar degree of fiber wall D/IF despite having a large difference in refining energy input (420 kW h odt in LC than in HC refining. The characteristic of the external fiber development from HC and LC refining was very different. Secondary LC refining promoted fiber surfaces with ribbons of thin hairlike threads arising from the inner secondary S2 layer that occasionally developed along the whole fiber length. Broad sheet- and lamellaetype external fibrillation from the S2 was typical for HC refining, and these characteristics were rarely observed in the LC pulps. The mechanisms for LC and HC fiber development are proposed. The cell wall characteristics (internal and external) of the pulp fibers appear to govern most of the physical and optical properties in handsheets.Primary refined softwood was subjected to highconsistency-1 ), confirming that D/IF was promoted more energyefficiently Keywords: (D/IF), fiber characterization, fiber development, surface ultrastructure of fibers, HC refining, LC refining, SEM, Simons’ stainingATMP, delamination/internal fibrillation
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| 22. |
- Fernando, Dinesh, et al.
(författare)
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Fundamental understanding of pulp property development under different thermomechanical pulp refining conditions as observed by a new Simons' staining method and SEM observation of the ultrastructure of fibre surfaces
- 2011
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 65:6, s. 777-786
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Tidskriftsartikel (refereegranskat)abstract
- The morphological and chemical characteristics of cell walls govern the response of wood fibre to mechanical pulping processes and thereby influence the energy efficiency of the process and determine most pulp and paper properties. A study has been carried out at the microstructural/ultrastructural level of fibre cell walls by means of a newly developed Simons' staining (SS) method and scanning electron microscopy to characterize thermomechanical pulps (TMPs) produced under different refining conditions. The SS method allows assessment and quantification of pulp fibre development during the process in terms of cell wall delamination/internal fibrillation (D/IF) under differentprocess conditions, and the degree of D/IF can be statistically evaluated for different TMP types. In focus was never-dried Norway spruce TMP from primary stage double-disc refining running in a full-scale mill, where specific refining energy was varied at different refining pressure levels. Improved energy efficiency was gained at the same tensile index level when applying high pressure (temperature). Under conditions of high pressure and refining energy, a significant enhancement of the degree of D/IF of pulp fibres was observed. The surface ultrastructure of these fibres exhibited an exposed S2 layer with long ribbon-type fibrillation compared to pulps produced with lower pressure and energy input. A given TMP type can be classified in the categories of high-severity and low-severity changes and quasi-untreated concerning the degree of D/IF of its fibres. The relative proportions of these are important for the development of pulp properties such as tensile strength. The presence of higher amounts of fibre fractions in the categories high D/IF and low D/IF will improve the tensile index of a TMP. © 2011 by Walter de Gruyter Berlin Boston.
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| 23. |
- Fernando, Dinesh, et al.
(författare)
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Surface and internal micro/ultrastructure of TMP fibres produced during high-intensity refining elucidate the development of pulp and paper properties
- 2012
-
Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 66:4, s. 467-475
-
Tidskriftsartikel (refereegranskat)abstract
- Refining during mechanical pulping causes delamination and internal fibrillation (D/IF) of the fibre wall and changes the surface ultrastructure. Fundamental knowledge about these phenomena at the fibre cell wall level helps our understanding of the development of pulp and paper properties, which in turn facilitates the optimization of processes, helping to save energy and improve the characteristics of final products. In the present study, pulps were produced by double-disc (DD) refined thermomechanical processes (DD-TMP) and have been characterized at the fibre cell wall micro/ultrastructural level based on Fernando and Daniel’s method (2010) of Simons ’ staining and scanning electron microscopy (SEM). The pulps studied were never-dried Norway spruce DD-TMP from a full-scale mill trial running under different process conditions; a) varying refining intensity, achieved by using a high-intensity turbine segment (HTS) and a standard (Ref) segment from Metso, and b) varying specific energy consumption (SEC). Improved energy efficiency was obtained with HTS segments, giving adequate or better pulp properties with respect to elongation, light scattering, Canadian Standard Freeness (CSF) at a similar tensile index level and lower energy consumption. Energy efficiency was gained through an elevated degree of D/IF and S2 fibrillation with low energy input. Both the SEC and segment designs had a significant impact on elevating the degree of D/IF. Statistical evaluation of fibre development with respect to D/IF gave evidence for improved energy efficiency in HTS refining. Ultrastructural studies on fibre surfaces showed that HTS refining produced better external fibrillation and leads to exposing the secondary S2 wall as fibre outer layer with different ribbon-type S2 fibrillation. Information obtained at the fibre wall level concerning D/IF and surface ultrastructure contribute to the fundamental knowledge about the pulp and handsheet properties and the energy efficiency of TMP processing. Copyright © by Walter de Gruyter·Berlin·Boston.
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| 24. |
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| 25. |
- Gao, Jie, et al.
(författare)
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Chemical and ultrastructural changes in compound middle lamella (CML) regions of softwoods thermally modified by the Termovuoto process
- 2014
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 68, s. 849-859
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Tidskriftsartikel (refereegranskat)abstract
- Silver fir and Norway spruce wood have been thermally modified (TMW) for 3-4 h at 160 degrees C, 180 degrees C, 200 degrees C, and 220 degrees C by means of the thermovacuum process (Termovuoto), and the ultrastructural and chemical changes in the compound middle lamella (CML), including the middle lamella cell corner (MLcc) regions (CMLcc), were investigated. Severe anatomical and histochemical changes were prominent above treatment temperatures of 200 degrees C; thus, woods treated at 220 degrees C for 4 h were in focus. Immunocytochemical studies showed that noncellulosic polysaccharides, such as pectin, xyloglucan, xylan, and mannan, were significantly degraded in CMLcc regions of TMWs. After treatment, the CMLcc regions were composed almost entirely of modified lignin with increased amounts of acidic groups. With cytochemical staining for lignin, many electron dense particulates were detected in the CMLcc regions of TMWs, indicating early degradation/alteration by the Termovuoto treatment.
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| 26. |
- Gebremeskel, Getachew Gizaw, et al.
(författare)
-
Determination of lignin content in kraft black liquors by capillary zone electrophoresis (CZE)
- 2013
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; :8, s. 887-890
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Tidskriftsartikel (refereegranskat)abstract
- Capillary zone electrophoresis (CZE) in an alkaline glycine buffer is suggested for the quantification of lignin content in black liquors (BL). The method was first tested by an external calibration with LignoBoost lignins. Then, the lignin content in BL was determined by means of a multivariate calibration with the application of a standard normal variate filter and partial least squares approach based on five principal components. The results are in agreement with those obtained by sulfuric acid lignin precipitation combined with ultraviolet measurement of the lignin in solution. The advantage of the CZE method is its independence from the knowledge of the exact absorptivity coefficient, which is needed for direct spectrophotometric lignin determination. Moreover, interfering substances and degradation products could be recognized and excluded from lignin determination; thus, the selectivity was increased significantly.
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| 27. |
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| 28. |
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| 29. |
- Gorski, Dmitri, et al.
(författare)
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Refiner bleaching in a peroxide-based ATMP process compared with conventional bleaching
- 2012
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 66:3, s. 275-281
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to compare refiner bleaching with conventional laboratory bleaching by means of hydrogen peroxide and magnesium hydroxide. Refiner bleaching in this study was a part of the ATMP (advanced thermo mechanical pulping) process, in which bleaching chemicals are added to the first stage refiner. Unbleached reference pulp which underwent similar mechanical treatment as refiner bleached pulp was used for laboratory bleaching. Bleaching efficiency was found to be almost equal for pilot scale refiner bleaching and conventional laboratory bleaching. A brightness increase of 10 ISO was reached with addition of 26 kg t -1 hydrogen peroxide leading to a final brightness of 66 ISO using both methods. Slightly more COD (52kg t -1 compared with 46 kg t -1) was generated in refiner bleaching compared with conventional laboratory bleaching to equal brightness with the same chemicals added. © 2012 by Walter de Gruyter Berlin Boston 2012.
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| 30. |
- Gosselink, Richard J. A., et al.
(författare)
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Effect of periodate on lignin for wood adhesive application
- 2011
-
Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 65:2, s. 155-162
-
Tidskriftsartikel (refereegranskat)abstract
- Development of eco-friendly binders with no harmful emission during its complete life cycle is of high interest for the wood-based industry. In this paper, a fully renewable binder based on activated lignin and poly-furfuryl alcohol and a partly renewable lignin based phenol-formaldehyde (PF) binder were evaluated. Activation of kraft and soda lignins, isolated respectively from softwood and non-woods, by periodate oxidation was performed to improve lignin reactivity and application in wood adhesives. Periodate oxidation of lignin leads to higher lignin acidity, formation of quinonoid groups under more severe conditions, higher molar mass and higher reactivity towards the curing of furfuryl alcohol within a temperature range currently used in industry. Comparison of a 100% furan-based glue with a furan-based glue substituted by 10% lignin yields comparable product properties. However, periodate-activated lignin leads to lower wood failure, which might be caused by incompletely solubilised lignin particles in the acidic formulation disturbing crosslinking of the furan resin. Unmodified softwood kraft lignin performs well in a PF resin formulation at substitution levels up to 30% (w/w). Periodate oxidation of soda lignins enhances the glue performance because higher wood failure is attained. The higher molar mass after periodate treatment could be an important parameter for development of a stronger wood binder.
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| 31. |
- Gosselink, Richard J. A., et al.
(författare)
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Fractionation, analysis, and PCA modeling of properties of four technical lignins for prediction of their application potential in binders
- 2010
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 64:2, s. 193-200
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Tidskriftsartikel (refereegranskat)abstract
- Functional properties of technical lignins need to be characterized in more detail to become a higher added value renewable raw material for the chemical industry. The suitability of a lignin from different plants or trees obtained by different technical processes can only be predicted for selected applications, such as binders, if reliable analytical data are available. In the present paper, structure dependent properties of four industrial lignins were analyzed before and after successive organic solvent extractions. The lignins have been fractionated according to their molar mass by these solvents extractions. Kraft and soda lignins were shown to have different molar mass distributions and chemical compositions. Lignin carbohydrate complexes are most recalcitrant for extraction with organic solvents. These poorly soluble complexes can consist of up to 34% of carbohydrates in soda lignins. Modeling by principle component analysis (PCA) was performed aiming at prediction of the application potential of different lignins for binder production. The lignins and their fractions could be classified in different clusters based on their properties, which are structure dependent. Kraft soft-wood lignins show the highest potential for plywood binder application followed by hardwood soda lignin and the fractions of Sarkanda grass soda lignin with medium molar mass. Expectedly, the softwood lignins contain the highest number of reactive sites in ortho positions to the phenolic OH group. Moreover, these lignins have a low level of impurities and medium molar mass.
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| 32. |
- Hafrén, Jonas, et al.
(författare)
-
Optical properties of thermomechanical pulp (TMP) obtained from sulfite-pretreated Norway spruce with focus on two-photon spectral imaging (TPSI)
- 2012
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 66:7, s. 817-824
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Tidskriftsartikel (refereegranskat)abstract
- Chips of Norway spruce have been impregnated with Na2SO3 and refined at two specific energy consumptions levels at full mill scale. The optical properties of thermomechanical pulps (TMPs) obtained were analyzed in terms of brightness, light scattering, opacity, and autofluorescence by spectral imaging. Even at low sulfite dosage (0.24% sulfite by dry weight) light absorption was reduced, and the brightness was elevated, and a clear dose-response effect was observed. Two-photon spectral imaging (TPSI) showed that sulfonation, impregnation, and refining affect the fluorescence properties differently. Compared to native wood, both processed wood chips and pulp fibers revealed blue-shifted fluorescence maxima, a characteristic of shortened conjugated systems. Two subpopulations of fibers with different optical properties were observed, and the fluorescence of one fiber population was red shifted.
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| 33. |
- Hafrén, Jonas
(författare)
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Proposed supramolecular structure of lignin in softwood tracheid compound middle lamella regions
- 2012
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 66, s. 907-915
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Tidskriftsartikel (refereegranskat)abstract
- The structure of lignin in the compound middle lamella (CML) of softwood tracheids differs from that in the secondary wall (SW) in regard to the content of condensed structures (5-5'-biphenyl, dibenzodioxocin and 4-O-5'-diphenyl ether). In an early stage of cell wall formation, random coarse networks composed of thin cellulose microfibrils (CMFs), hemicelluloses, and pectin are formed in the CML, then globular p-hydroxyphenyl/guaiacyl lignin (HG-lignin) is deposited quickly into the network. The globular lignin is assumed to be a micellar aggregate of oligolignols folded at the beta-O-4 bond with their phenolic ends on the outer part of the aggregate. When 3D clusters of the globules are deposited on the preformed network of polysaccharides, further growth of the oligolignols by endwise addition of new monolignols is spatially limited, so frequent condensation occurs between growing aromatic ends of adjacent HG-oligolignols within the globule and between the wide contact boundaries of the 3D clustered globules to produce a highly condensed supramolecule in CML. In SW, the folded G-oligolignols are deposited slowly in the narrow tubular space surrounding thick CMFs coated with hemicelluloses. Condensation occurs mostly between adjacent growing ends of the oligolignols within the tubular aggregates. Spatial regulation of condensation of folded polylignols is one of the factors producing a different supramolecular structure for CML lignin than for SW lignin.
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| 34. |
- Hellström, Lisbeth M., et al.
(författare)
-
A theoretical and experimental study of the circular sawing process
- 2014
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 68:3, s. 307-312
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Tidskriftsartikel (refereegranskat)abstract
- To gain further insight into the energy dissipation during the wood sawing process, a theoretical model has been developed. The model is based on the assumption that there are two basic causes for energy dissipation during sawing: the creation of a new surface and the compression of material below a saw tooth. It is assumed that both contributions can be dependent on the cutting angle (the angle between the fiber direction and the tangent to the path followed by a saw tooth) because a saw tooth changes its angle of attack during its way through a log. To determine this dependence of the dissipation on the cutting angle, a series of experiments with pine plank sawing were performed by means of different feeding rates and cutting angles while the electrical power supplied to the saw was measured. The parameters in the theoretical model were derived from the experimental findings. Finally, two tests were carried out under different conditions with respect to thickness and cutting angles and the validity of the model was confirmed concerning the prediction of the electrical power consumption.
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| 35. |
- Hellström, Lisbeth, 1969-, et al.
(författare)
-
Properties of wood chips for thermomechanical pulp (TMP) production as a function of spout angle
- 2011
-
Ingår i: Holzforschung. - : Walter de Gruyter. - 0018-3830 .- 1437-434X. ; 65:6, s. 805-809
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Tidskriftsartikel (refereegranskat)abstract
- Spruce woodchipswere produced under well-controlled conditions in a laboratory woodchipper at spout angles of 30°, 40°, and 50° at a cutting rate of 20 m s-1 and with a nominalchip length of 25 mm. Thechips were then refined under thermomechanical pulp (TMP) conditions in a pilot refiner plant. The pulpproperties such as freeness, average fiber length, and shives content were determined and evaluated as a function of specific energy consumption. For a first stage refining and for a freeness value of 350 ml, a decrease in specific electrical energy consumption could be achieved by performing thewood chipping at a spout angle of 50° as compared to 30° which is the spout angle commonly used. A patent application regarding this method has been filed and is pending. It is realized that a freeness value is not directly indicative of any quality measure, such as, for example tensile index and light scattering coefficient but the obtained results can be interpreted to be promising. Further studies are needed regarding the impact of the modified chipping process.
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| 36. |
- Illergård, Josefin, et al.
(författare)
-
Tailoring the effect of antibacterial polyelectrolyte multilayers by choice of cellulosic fiber substrate
- 2013
-
Ingår i: Holzforschung. - : Walter de Gruyter. - 0018-3830 .- 1437-434X. ; 67:5, s. 573-578
-
Tidskriftsartikel (refereegranskat)abstract
- There is a need for new, antibacterial cellulose-based materials. Antibacterial cellulosic fibers with irreversibly attached polyvinylamine (PVAm) and polyacrylic acid (PAA) in multilayers were developed based on a water-based physical adsorption process. The antibacterial substance is thus prevented from leaching, in contrast to materials containing, for example, silver. It was shown on fibers from different sources that the antibacterial effect against both Escherichia coli and Bacillus subtilis can be tailored. The efficiency correlated with the initial fiber charge, which in turn correlated with the amount of adsorbed PVAm. In the case of highly charged fibers, the antibacterial efficacy was more than 99.9%. A sustainable antibacterial material can be obtained in a simple way based on a water-based process.
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| 37. |
- Isaksson, Per, et al.
(författare)
-
A numerical and experimental study regarding the influence of some process parameters on the damage state in wood chips
- 2013
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 67:6, s. 691-696
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Tidskriftsartikel (refereegranskat)abstract
- The specific energy consumption during mechanical refining operation can be reduced by choosing the optimal process parameters in the wood chipping process such that a beneficial pretreatment is obtained. In the case of the utilization of a larger knife-edge angle, which is one such process parameter, the energy reduction is presumably due to the increased compressive loading parallel to the wood fibers. In the present article, a chip damage parameter D of spruce is in focus, which is relevant for cracking parallel to the fibers. D is defined and its dependence on the chip length and edge angle of the chipping knife is analyzed numerically by means of finite element analyses (FEA). The cutting force was measured in a pilot wood chipper for a number of knife-edge angles. There is a good correlation between the experimental results and those of FEA.
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| 38. |
- Kihlman, Martin, et al.
(författare)
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Dissolution of dissolving pulp in alkaline solvents after steam explosion pretreatments
- 2011
-
Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 65:4, s. 613-617
-
Konferensbidrag (refereegranskat)abstract
- In this project different aqueous based solvent systems were investigated for the dissolution of steam exploded (STEX) dissolving pulps prior to a coagulation step for preparation of textile fibers. The pulp samples studied could, to a large degree, be dissolved in a NaOH/urea/thiourea system, but there are always residuals, irrespective of the conditions. The dissolution process appeared to be kinetically controlled, as prolonged retention time decreased the amount of residuals. A pre-cooled NaOH/urea/thiourea system, and a retention time of 60 h generated the lowest amount (6%) of residuals of the STEX pretreated dissolving pulp studied. Some fundamental results are described and a model for dissolution of dissolving pulp fibers is proposed.
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| 39. |
- Kihlman, Martin, 1986-, et al.
(författare)
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Effect of Various Pulp Properties on The Solubility of Cellulose in Sodium Hydroxide Solutions
- 2012
-
Ingår i: Holzforschung. - Berlin : Walter de Gruyter. - 0018-3830 .- 1437-434X. ; 66:5, s. 601-606
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Tidskriftsartikel (refereegranskat)abstract
- The dissolution of pulps with varying characteristic properties, for example cellulose chain length or content of hemicellulose, has been investigated in two alkaline solvent systems [sodium hydroxide (NaOH)/urea/thiourea (8:8:6.5 by wt.) and NaOH/zince oxide (ZnO) (9:0.5 by wt.)]. One standard paper pulp, two dissolving pulps and three pretreated pulps were selected for this study. The dissolution parameters in focus were the fiber dimensions, average degree of polymerization (DP), polydispersity, water retention value and content of hemicelluloses. The solubility was not influenced by the fiber dimensions. The only significant properties, according to variable importance plot, were DP and composition of the hemicelluloses. It was also established that mass transfer effects during the dissolution stage plays an important role in the dissolution of cellulose derived from pulp fibers.
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| 40. |
- Kolavali, Reddysuresh, 1983, et al.
(författare)
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Determination of the diffusion of monovalent cations into wood under isothermal conditions based on LiCl impregnation of Norway spruce
- 2013
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 1437-434X .- 0018-3830. ; 67:5, s. 559-565
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Tidskriftsartikel (refereegranskat)abstract
- The impregnation of wood pieces in the course of pulping can be divided into primary (advective masstransport) and secondary (diffusive mass transport) penetration.Little is known about the latter partly because of the difficulties in the determination of the relevant diffusivities for this system. In the present article, a precise experimental methodology has been developed to measure the concentration profiles of cations as a function of wood piece dimensions, impregnation time, temperature,and wood structure. The cation concentration can be measured at any position in the impregnated wood piece.The impregnation of Norway spruce wood samples with LiCl was investigated. The impregnated wood pieces were cut mechanically into cubes, which were cut in slices by means of a microtome, and the eluate of the 0.4-mm-thick slices in HNO 3 was analyzed by flame atomic emission spectroscopy. The method gave reasonable results, and defects in the wood piece (microcracks) were detectable.The preliminary results presented here have to be verifiedwith more replicates due to the heterogeneity of wood.
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| 41. |
- Konnerth, Johannes, et al.
(författare)
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Macro- and micro-mechanical properties of red oak wood (Quercus rubra L.) treated with hemicellulases
- 2010
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 64:4, s. 447-453
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Tidskriftsartikel (refereegranskat)abstract
- Red oak wood (Quercus rubra L.) samples were submitted to an enzymatic treatment with a commercial mixture of hemicellulases aiming at the selective depolymerization and removal of the hemicelluloses. Mechanical properties of treated samples were characterized and compared with untreated samples at two hierarchical levels. At the macrolevel, tensile properties revealed to be less sensitive to degradation of the cell wall matrix compared to compression and hardness properties. Results obtained through indentation at the microlevel indicated that hardness and the so-called reduced modulus of treated wood were significantly lowered. Accordingly, hardness and reduced elastic modulus have proven to be most sensitive to modification of the cell wall matrix by reducing the content of hemicelluloses. It is proposed that transversal and shear stresses, which are mainly carried by the cell wall matrix, are additional parameters having strong effects on elastic modulus obtained by nanoindentation. Micromechanical modeling was employed to confirm the observed changes. There is consistency between the measured and the modeled properties, obtained at both the microlevel and the macrolevel of wood.
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| 42. |
- Larsen, Finn, et al.
(författare)
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Experimental and finite element study of the effect of temperature and moisture on the tangential tensile strength and fracture behavior in timber logs
- 2014
-
Ingår i: Holzforschung. - : Walter de Gruyter. - 0018-3830 .- 1437-434X. ; 68:1, s. 133-140
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Tidskriftsartikel (refereegranskat)abstract
- Timber is normally dried by kiln drying, in the course of which moisture-induced stresses and fractures can occur. Cracks occur primarily in the radial direction due to tangential tensile strength (TSt) that exceeds the strength of the material. The present article reports on experiments and numerical simulations by finite element modeling (FEM) concerning the TSt and fracture behavior of Norway spruce under various climatic conditions. Thin log disc specimens were studied to simplify the description of the moisture flow in the samples. The specimens designed for TS were acclimatized to a moisture content (MC) of 18% before TSt tests at 20°C, 60°C, and 90°C were carried out. The maximum stress results of the disc simulations by FEM were compared with the experimental strength results at the same temperature levels. There is a rather good agreement between the results of modeling and experiments. The results also illustrate the strong decrease of TSt with increasing temperature at a constant MC level.
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| 43. |
- Larsson, Per Tomas, et al.
(författare)
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Influence of cellulose supramolecular structure on strength properties of chemical pulp
- 2014
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 68:8, s. 861-866
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Tidskriftsartikel (refereegranskat)abstract
- The industrially produced chemical pulps have lower strength properties than those obtained under laboratory conditions, and this difference is referred to as the strength delivery (SD) problem. In this study, the hypothesis was put forward that the SD could, at least in part, be accounted for by the supramolecular structure of the cellulose microfibrils of the fiber wall. To test the hypothesis, two bleached softwood kraft pulps (BSKP) were manufactured from the same starting material with different degrees of cellulose aggregation, but the pulps were otherwise as similar as possible in other controllable respects. The chemical and physical properties, including the pulp strength, were tested. A selective increase of the degree of cellulose microfibril aggregation resulted in a pulp with a decreased tear index (TI) at a specified tensile index, and this decrease was similar in magnitude to what is typically encountered in SD. Accordingly, the current experimental study succeeded in mimicking the SD problem. The lateral fibril aggregate dimensions (LFAD) seem to play a pivotal role and it can be safely concluded in general that the supramolecular structure of cellulose in the fibers may be an important factor contributing to the SD problem.
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| 44. |
- Leppänen, Kirsi, et al.
(författare)
-
X-ray scattering and microtomography study on the structural changes of never-dried silver birch, European aspen and hybrid aspen during drying
- 2011
-
Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 65:6, s. 865-873
-
Tidskriftsartikel (refereegranskat)abstract
- The impact of drying on the structure of the never-dried hardwood cell wall was studied at nanometer level by means of wide- and small-angle X-ray scattering (WAXS, SAXS), and at micrometer level by X-ray microtomography (mu CT). Never-dried silver birch, European aspen and hybrid aspen samples were measured by WAXS in situ during drying in air. The samples included juvenile and mature wood, as well as normal and tension wood to allow comparison of the effects of different matrix compositions and microfibril angles. The deformations of cellulose crystallites and amorphous components of the cell wall were detected as changes in the cellulose reflections 200 and 004 and amorphous halo in the WAXS patterns. Especially, the width of the reflection 004, corresponding to the cellulose chain direction, increased due to drying in all the samples, indicating an increase of strain and disorder of the chains. Also, the cellulose unit cell shrank 0.2-0.3% during drying in this direction in all the samples except in hybrid aspen tension wood. According to the SAXS results of silver birch, the distance between microfibrils decreased during drying. It was detected by mu CT that the mean cross-sectional maximum width of the parenchymatous rays decreased from that of never-dried to air-dried birch by roughly 16%.
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| 45. |
- Li, Dongfang, et al.
(författare)
-
Pretreatment of softwood dissolving pulp with ionic liquids
- 2012
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 66:8, s. 935-943
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Tidskriftsartikel (refereegranskat)abstract
- Few Scandinavian pulp mills produce dissolving pulps; however, the demand on textile fibers is increasing. This study investigates the chemical interaction of dissolving pulp with ionic liquids (ILs), where softwood and hardwood industrial dissolving pulps were pretreated with ILs 1-butyl-3-methyl-imidazolium acetate ([C(4)mim(+)]CH3COO-) and 1-butyl-3-methyl-imdazolium chloride ([C(4)mim(+)]Cl-). Time and temperature dependence of the dissolution process as well as the impact of the pretreatment on the molecular weight properties, thermal stability, morphology, and crystallinity of the cellulose were evaluated by means of size exclusion chromatography (SEC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray diffraction (XRD), and solid state nuclear magnetic resonance (NMR). It was shown that the dissolution of cellulosic material in ILs is a temperature-dependent process; however, the viscosity of ILs affected the efficiency of dissolution at a given temperature. Molecular weight properties were affected negatively by increased dissolution temperature, while the type of antisolvent for the regeneration had no major impact on the degree of polymerization of cellulose. Water was more efficient than ethanol for the regeneration of cellulose when performed at an elevated temperature. The pretreatment decreased the crystallinity of cellulosic material. This might lead to the increased accessibility and reactivity of cellulose.
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| 46. |
- Li, Jiebing, et al.
(författare)
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Fractionation and characterization of lignin-carbohydrate complexes (LCCs) from eucalyptus fibers
- 2011
-
Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 65:1, s. 43-50
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Tidskriftsartikel (refereegranskat)abstract
- The effect of milling time on the structure of lignin was investigated by analyzing the quantity and molecular size distribution of thioacidolysis products obtained from wood and pulp of eucalypt (Eucalyptus globulus). After milling, the ability of three solvent systems was determined to completely dissolve the wood or pulp meal. It was found that a mixture of DMSO and 50% aqueous tetrabutylammonium hydroxide was superior to either dimethylacetamide-LiCl or DMSO-tetrabutylammonium fluoride as solvent. By applying the minimum milling time required for complete dissolution, structurally unaltered wood or pulp could be further separated into lignin-carbohydrate fractions. These were analyzed by thioacidolysis. From eucalypt pulp, two different lignin-carbohydrate fractions were obtained, one glucan-and one xylan-enriched fraction, with the latter having more syringyl units in its lignin moieties. The developed solvent system seems to be universal because spruce and flax fibers and pulps could also be dissolved in it after milling.
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| 47. |
- Mahnert, K-C, et al.
(författare)
-
Topochemistry of heat-treated and N-methylol melamine modified wood of Koto (Pterygota macrocarpa K. Schum.) and Limba (Terminalia superba Engl. et Diels)
- 2013
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 67:2, s. 137-146
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Tidskriftsartikel (refereegranskat)abstract
- To broaden the knowledge about the chemical changes at the cell wall level of differently modified tropical hardwoods, heat-treated and N-methylol melamine (NMM)-treated samples of koto (Pterygota macrocarpa) and limba (Terminalia superba) were prepared. UV microspectrophotometry (UMSP) was applied at 278 and 240 nm as specific wavelengths to analyze chemical alterations of the samples caused by heat and NMM treatment, respectively. The absorbance of koto exceeded that of limba before and after treatment, potentially due to the higher extractive content of the former. Regardless of the wood species, the absorbance of the samples increased with increasing intensity of the NMM treatment. Additionally, the absorbance of lignin within the spectrum of 230–350 nm was altered due to the NMM treatment. The functionality of applying specific wavelengths for the analysis of different modification methods of wood was proven. However, the comparison with literature did not show differences in the absorbance, which could be assigned to the characteristics of tropical hardwoods.
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| 48. |
- Martín, Carlos, et al.
(författare)
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Optimization of sulfuric acid-assisted glycerol pretreatment of sugarcane bagasse
- 2013
-
Ingår i: hfsg. - : De Gruyter Open. - 1437-434X .- 0018-3830.
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- A combined pretreatment of sugarcane bagasse with glycerol and sulfuric acid was investigated based on a central composite rotatable experimental design. The following factors were varied: temperature (150–199°C), time (0.69–2.3 h), H2SO4 concentration (0.0–1.1%), and glycerol concentration (55.4–79.6%). Xylans and lignin were considerably solubilized during pretreatment. Xylan solubilization, ranging between 6% and 94%, increased significantly with the increase of temperature, time, and H2SO4 concentration and dropped with the increase of glycerol amount. Glycerol restricted the solubilization and full hydrolysis of xylans and the degradation of xylose. Lignin solubilization (20.6–49.4%) increased with the increase of all the experimental factors. Cellulose recovery, which was generally high, increased with the increasing of glycerol concentration and declined at high levels of the other factors. Recoveries above 97% were achieved at low H2SO4 concentration and high glycerol load, whereas the lowest value (83.4%) was achieved in the longest-lasting experiment. The models based on the experimental results predicted the maximal lignin solubilization at 187.7°C, 2.3 h, 79.6% glycerol, and 0.64% H2SO4, whereas the highest yield of enzymatic hydrolysis can be expected at 194.1°C, 1.67 h, 79.6% glycerol, and 1.1% H2SO4. The optimal conditions were confirmed in control experiments. The synergistic effect of sulfuric acid and glycerol on the enzymatic hydrolysis of cellulose was demonstrated.
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| 49. |
- Nilsson, Urban
(författare)
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Effects of timing and intensity of thinning on wood structure and chemistry in Norway spruce
- 2010
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 64, s. 81-91
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Tidskriftsartikel (refereegranskat)abstract
- The effects of thinning intensity on wood structure and chemistry of Norway spruce [Picea abies (L.) Karst.] have been studied in a long-term thinning experiment established in the 1960s in south-western Sweden. The experiment comprised datasets of unthinned control trees and trees of four thinning treatments, in which thinning operations of different intensities were carried out. These thinning operations were applied either once, three, or five times over the course of the stand rotation. Thinning intensities varied from 0% to 60% based on the stand basal area (BA) before thinning: (A) 5 x 20% (i.e., 20% of the BA removed five times); (B) 3 x 40% (i.e., 40% of the BA removed three times); (C) 1 x 60% (i.e., 60% of the BA removed once); and (D) 5 x 40% (i.e., 40% of the BA removed five times). Altogether 60 trees that were 67 years old were sampled 38 years after the treatment onset. Radial growth rate, wood density, tracheid properties, and the chemical composition of wood were studied in detail. All four thinning treatments increased growth rate and decreased wood density; however, treatment D showed the greatest change. Single, heavy thinning in treatment C resulted in unfavourable intra-stem variation in ring width and wood density. No significant differences in tracheid properties and wood chemistry were found between the treatments. We conclude that only a remarkable increase in growth rate would induce detrimental changes in tracheid properties and wood chemistry in the context of thinning.
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| 50. |
- Norbakhsh, Shahin, et al.
(författare)
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Impact of iron(II) and oxygen on degradation of oak - modeling of the Vasa wood
- 2014
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 68:6, s. 649-655
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Tidskriftsartikel (refereegranskat)abstract
- In the wood of the Swedish 17th century warship Vasa, iron (Fe)-catalyzed chemical degradation has taken place after the salvation in 1961, which is manifested in increased acidity accompanied by cellulose degradation and reduced strength in the oak hull. Model studies on fresh oak impregnated with Fe(II) also led to tensile strength (TS) reduction in the same order of magnitude as observed in the wood of the Vasa. In the present study, further experiments have been performed concerning the Fe-catalyzed wood degradation. Namely, the degree of wood degradation was monitored quantitatively by measurement of the O-2 consumption of Fe(II)-impregnated oak, kept in closed vials with different relative humidities (RH), as a function of time. The initial O-2 consumption was high and declined with time. After 200 days, the accumulated O-2 consumption was 0.3-0.4 mmol g(-1) wood. Degradation products with low molecular weight were analyzed. The release of CO2 and oxalic acid (OA) was positively correlated with RH (0.235 and 0.044 mmol g(-1), respectively, at RH98% after 200 days). Samples kept for 1500 days at RH54% had accumulated 0.044 mmol OA g(-1) wood, which is equal to the average OA content in the interior of Vasa oak (corresponding to 4 mg g(-1)). Oak samples, from which extractives had been removed prior to Fe(II) impregnation, did not change their O-2 consumption or TS reduction compared to the nonextracted samples, indicating that extractives are not essential for cellulose degradation in this context.
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