| 1. |
- Abdel Hady, Ahmed Wagih Abdallah, 1990, et al.
(författare)
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In situ microstructural evolution of spruce wood during soda pulping using synchrotron X-ray tomography
- 2022
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 1437-434X .- 0018-3830. ; 76:7, s. 611-621
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Tidskriftsartikel (refereegranskat)abstract
- A new laboratory reactor to perform in situ studies of structural changes in wood during soda pulping using synchrotron X-ray tomography is presented. The reactor is of recirculation type to provide stable reaction conditions and mimic the industrial situation. Experiments have been performed using this reactor in situ at a synchrotron microtomography beamline to provide sequences of 3D images from which measurement of wood cell wall thickness have been possible for the first time. The results showed that the cell wall thickness increased significantly in the early stage of pulping (<10 min), which is due to the transportation of cooking chemicals through the tracheids, resin channels and pits into the cell wall, which is swollen with the increased pH. Subsequently, the cell wall thickness reduces over the processing time up to 60 min with a high rate, which is inferred to be due to the dissolution and transport of lignin and hemicellulose from the secondary walls, allowing for better transportation of active chemicals deep through the cell wall layers. After 60 min processing, the cell wall thickness reduction rate reduced, as dissolution of lignin and hemicelluloses from the cell walls ceased, while the remaining dissolution occurs mainly at the middle lamella.
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| 2. |
- Abdel Hady, Ahmed Wagih Abdallah, 1990, et al.
(författare)
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Micro/nano-structural evolution in spruce wood during soda pulping
- 2021
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 1437-434X .- 0018-3830. ; 75:8, s. 754-764
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Tidskriftsartikel (refereegranskat)abstract
- Alkaline delignification of wood tissue is the core of the global pulping technology and the most prominent large-scale separation of the main wood components. This work aims at improved understanding of the interplay between the topochemistry of alkaline pulping and the associated morphological changes. Morphology and chemical structure of partially soda-delignified wood chips were studied combining X-ray tomography (XRT), X-ray diffraction analysis and compositional characterization (lignin and carbohydrate content). The XRT studies of wet samples (providing 3D structural information without interfering drying effects), allowed observation of the cell wall separation as an increasing amount of lignin was removed with the increasing pulping time. Comparison between the microstructure of the surface and the central parts of the treated chips showed a more delignified microstructure at the surface, which highlights the dependence of the delignification process on the mass transport (hydroxide ions and lignin fragments) through the wood tissue. The crystallite size of cellulose increased in the <200> crystal planes during the early stage of pulping while there was little effect on the <110> plane.
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| 3. |
- Ahlbom, Anders, 1993, et al.
(författare)
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On the hydrothermal depolymerisation of kraft lignin using glycerol as a capping agent
- 2023
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 1437-434X .- 0018-3830. ; 77:3, s. 159-169
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Tidskriftsartikel (refereegranskat)abstract
- Depolymerisation of kraft lignin under hydrothermal conditions was investigated at short residence times (1–12 min) with glycerol being used as a capping agent. The weight average molecular weight (M w) of the products decreased within the first minute of residence time, with the inter-unit ether linkages breaking accordingly. Furthermore, the M w of the product fractions decreased at increasing residence times, while the char yield increased. Short residence times thus appear to be beneficial for mitigating the formation of char. Also, addition of NaOH reduced the yield of char. Although the addition of glycerol caused a decrease in the M w of the products, it seemed to increase the yield of char and therefore might not be a suitable capping agent for kraft lignin depolymerisation.
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| 4. |
- Ahlbom, Anders, 1993, et al.
(författare)
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Towards understanding kraft lignin depolymerisation under hydrothermal conditions
- 2021
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 1437-434X .- 0018-3830. ; 76:1, s. 37-48
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Tidskriftsartikel (refereegranskat)abstract
- Kraft lignin depolymerisation using hydrothermal liquefaction suffers from the formation of char, resulting in a decreased product yield as well as causing operational problems. While this may be mitigated by the addition of capping agents such as phenol and isopropanol, other reaction parameters, for example reaction time and temperature, are also important for the product yields. In this work, the effect of short reaction times on the hydrothermal liquefaction of kraft lignin in an alkaline water and isopropanol mixture was investigated at 1-12 min and 290 °C. The results show that there were swift initial reactions: the major ether bonds in the lignin were broken within the first minute of reaction, and the molecular weight of all product fractions was halved at the very least. Longer reaction times, however, do not cause as pronounced structural changes as the initial reaction, indicating that a recalcitrant carbon-carbon skeleton remained in the products. Nevertheless, the yields of both char and monomers increased slowly with increasing reaction time. The swift initial depolymerising reactions were therefore followed by slower repolymerisation as well as a slow formation of monomers and dimers, which calls for careful tuning of the reaction time.
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| 5. |
- Bengtsson, Jenny, et al.
(författare)
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Preventing fiber-fiber adhesion of lignin-cellulose precursors and carbon fibers with spin finish application
- 2023
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Ingår i: Holzforschung. - : De Gruyter Open Ltd. - 0018-3830 .- 1437-434X. ; 77, s. 648-
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Tidskriftsartikel (refereegranskat)abstract
- Adhesion of fibers within a spun tow, including carbon fibers and precursors, is undesirable as it may interrupt the manufacturing process and entail inferior fiber properties. In this work, softwood kraft lignin was used together with a dissolving pulp to spin carbon fiber precursors. Lignin-cellulose precursors have previously been found to be prone to fiber fusion, both post-spinning and during carbon fiber conversion. In this study, the efficiency of applying different kinds of spin finishes, with respect to rendering separable precursors and carbon fibers, has been investigated. It was found that applying a cationic surfactant, and to a similar extent a nonionic surfactant, resulted in well separated lignin-cellulose precursor tows. Furthermore, the fiber separability after carbon fiber conversion was evaluated, and notably, precursors treated with a silicone-based spin finish generated the most well-separated carbon fibers. The underlying mechanism of fiber fusion post-spinning and converted carbon fibers is discussed.
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| 6. |
- Carlsson, Jenny, 1984-, et al.
(författare)
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Investigating tool engagement in groundwood pulping : finite element modelling and in-situ observations at the microscale
- 2020
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 74:5, s. 477-487
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Tidskriftsartikel (refereegranskat)abstract
- With industrial groundwood pulping processes relying on carefully designed grit surfaces being developed for commercial use, it is increasingly important to understand the mechanisms occurring in the contact between wood and tool. We present a methodology to experimentally and numerically analyse the effect of different tool geometries on the groundwood pulping defibration process. Using a combination of high-resolution experimental and numerical methods, including finite element (FE) models, digital volume correlation (DVC) of synchrotron radiation-based X-ray computed tomography (CT) of initial grinding and lab-scale grinding experiments, this paper aims to study such mechanisms. Three different asperity geometries were studied in FE simulations and in grinding of wood from Norway spruce. We found a good correlation between strains obtained from FE models and strains calculated using DVC from stacks of CT images of initial grinding. We also correlate the strains obtained from numerical models to the integrity of the separated fibres in lab-scale grinding experiments. In conclusion, we found that, by modifying the asperity geometries, it is, to some extent, possible to control the underlying mechanisms, enabling development of better tools in terms of efficiency, quality of the fibres and stability of the groundwood pulping process.
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| 7. |
- de Carvalho, Danila Morais, et al.
(författare)
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Impact of birch xylan composition and structure on film formation and properties
- 2020
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Ingår i: Holzforschung. - : Walter de Gruyter. - 0018-3830 .- 1437-434X. ; 74:2, s. 184-196
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Tidskriftsartikel (refereegranskat)abstract
- Commercial birch xylan (CX) and alkali-soluble birch xylan (ASX) were subjected to controlled acetylation and used for film formation in the presence (20% and 40%) or absence of plasticizers (i.e. glycerol, sorbitol and xylitol). Although the content of Klason lignin was similar (1.2-1.4%), the acetylation process was favored by the high-purity CX (97% xylan) over the ASX (89% xylan). On the other hand, the presence of residual pectin heteropolysaccharides rather than xylan in the ASX sample was beneficial for film formation. These heteropolysaccharides seemed to act as natural plasticizers during film formation, allowing the formation of coherent films from ASX, even in the absence of an external plasticizer. The use of plasticizers favored the mechanical properties of films, especially in a dosage of 40%, when plastic behavior was created. Acetylation favored the film formation and slightly improved the mechanical properties of the films, and this improvement was in the same range as that achieved when using 20% plasticizer in non-acetylated ASX.
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| 8. |
- Florisson, Sara, et al.
(författare)
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An overview of lab-based micro computed tomography aided finite element modelling of wood and its current bottlenecks
- 2023
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Ingår i: Holzforschung. - : Walter de Gruyter. - 0018-3830 .- 1437-434X. ; 77:11-12, s. 793-815
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Tidskriftsartikel (refereegranskat)abstract
- Microscopic lab-based X-ray computed tomography (XµCT) aided finite element (FE) modelling is a popular method with increasing nature within material science to predict local material properties of heterogeneous materials, e.g. elastic, hygroexpansion and diffusion. This method is relatively new to wood and lacks a clear methodology. Research intended to optimise the XµCT aided FE process often focuses on specific aspects within this process such as the XµCT scanning, segmentation or meshing, but not the entirety of the process. The compatibility and data transfer between aspects have not been investigated to the same extent, which creates errors that propagate and negatively impact the end results. In the current study, a methodology for the XµCT aided FE process of wood is suggested and its bottlenecks are identified based on a thorough literature review. Although the complexity of wood as a material makes it difficult to automate the XµCT aided FE process, the proposed methodology can assist in a more considered design and execution of this process. The main challenges that were identified include an automatic procedure to reconstruct the fibre orientation and to perform segmentation and meshing. A combined deep-learning segmentation method with geometry-based meshing can be suggested.
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| 9. |
- Florisson, Sara, et al.
(författare)
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Microscopic computed tomography aided finiteelement modelling as a methodology to estimatehygroexpansion coefficients of wood : a case studyon opposite and compression wood in softwoodbranches
- 2023
-
Ingår i: Holzforschung. - : Walter de Gruyter. - 0018-3830 .- 1437-434X.
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Tidskriftsartikel (refereegranskat)abstract
- Microscopic X-ray computed tomography (XµCT) aided finite element (FE) modelling is a popular method in material science to relate material properties to heterogeneous microstructures. Recently, a methodology was developed for the XµCT aided FE modelling of wood, which characterises the process from specimen preparation to estimation of material properties. In the current research, this methodology is tested on branches of Norway spruce (Picea abies (L.) Karst.) to estimate the hygroexpansion coefficients of opposite (OW) and compression wood (CW). These properties are largely unknown and have engineering implications. The study is complemented by measurements of density, moisture content (MC) and elastic moduli. Results showed that the methodology assisted in the design of an integrated process and the identification of bottlenecks. It was seen that the level of detail of the numerical model had a strong influence on the obtained hygroexpansion properties. CW from branches showed higher density and longitudinal shrinkage coefficients, and elastic moduli less affected by MC. These differences are unlikely caused by MC, but more likely by the characteristics of the microstructure.
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| 10. |
- Forsman, Karin, et al.
(författare)
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Moisture-dependency of the fracture energy of wood : A comparison of unmodified and acetylated Scots pine and birch
- 2021
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 75:8, s. 731-741
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Tidskriftsartikel (refereegranskat)abstract
- The moisture-dependency of the fracture energy for unmodified and acetylated Scots pine (Pinus sylvestris L.) and birch (Betula pendula Roth) has been investigated. Specimens were conditioned at relative humidity levels of 20, 75, and 97%, as well as dry and water-saturated. At moisture contents below 15%, the fracture energy increased with increasing moisture content for both unmodified and acetylated wood, while it decreased for untreated wood at higher moisture contents. A significant difference in moisture-dependency was found, indicating higher fracture energy for unmodified wood compared to acetylated wood at similar moisture contents. Additionally, to assess the impact of the increased brittleness for structural applications, the fracture energy was compared at equal relative humidity levels. The largest difference was seen at 75% relative humidity with approximately 50% lower fracture energy for acetylated wood. No significant differences were found for water-saturated samples. The moisture-dependency of the fracture energy, combined with the reduced hygroscopicity of acetylated wood, is suggested to be one, but not the only, contributing factor to the lower fracture energy of acetylated wood compared to unmodified wood at equal humidity levels. These observations have importance for structural design since design codes often assess material parameters based on ambient humidity.
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| 11. |
- Fredriksson, Maria, et al.
(författare)
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Artifacts in electrical measurements on wood caused by non-uniform moisture distributions
- 2021
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 75:6, s. 517-525
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Tidskriftsartikel (refereegranskat)abstract
- This paper examines how the moisture conditioning method affects the electrical conductance of wood. A widely used dataset was acquired by Stamm in 1929 who used a method of conditioning where water-saturated wood specimens were partially dried, sealed and left for a period of time for moisture to be redistributed before the electrical conductance was measured. However, more recent measurements combined conditioning above saturated salt solutions and pressure plate/pressure membrane techniques to obtain equilibrium moisture contents at constant relative humidity levels in the full moisture range. In this paper, the electrical conductance as a function of moisture content was compared for these two conditioning methods. When the specimens were conditioned to constant relative humidity levels, the data obeyed a percolation model better than when the conditioning procedure by Stamm was used. This was attributed to that Stamm's method gives moisture gradients through the specimen because of sorption hysteresis effects, even though the wood is conditioned to a steady-state moisture content. Equilibration to constant relative humidity levels thus provided more well-defined moisture states and that the data followed a percolation model indicates that the mechanism of electrical conduction in wood does not change, even at high moisture contents.
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| 12. |
- Ghavidel, Amir, et al.
(författare)
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Degradation assessment of archaeological oak (Quercus spp.) buried under oxygen-limited condition
- 2023
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Ingår i: Holzforschung. - : Walter de Gruyter. - 0018-3830 .- 1437-434X. ; 77:3, s. 198-207
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Tidskriftsartikel (refereegranskat)abstract
- The biological deterioration of archaeological wood under oxygen-limited conditions varies due to the limited activities of microorganisms. It is essential to expand the knowledge of the degradation types and the status of archaeological monuments for selecting the proper consolidates. The physical, chemical, and anatomical properties of approximately 600–650 year old archaeological oak collected from an archaeological site in Iasi-Romania were analysed to assess the quality and to identify the degradation types. The results were compared with similar tests on recently-cut oak. X-ray photoelectron spectroscopy (XPS) revealed the presence of more lignin-related peaks in the archaeological oak, which likely reflected the degradation of the wood carbohydrates as evidenced by the decreased oxygen-to-carbon ratio Cox/Cnon-ox. The differences in cellulose crystallinity were not significant suggesting that any cellulose degradation occurred in the amorphous regions. This was also reflected in the dynamic water vapor sorption analysis where the differences in sorption isotherms and hysteresis of archaeological and recently-cut oaks were marginal. Microscopic analysis of the oak cells illustrated bacterial degradation patterns, while the field emission scanning electron microscopy (FESEM) showed the presence of erosion bacteria in the archaeological oak collected from the site with low oxygen conditions.
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| 13. |
- Ghavidel, Amir, et al.
(författare)
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Photodegradation stability of huminated European pine (Pinus sylvestris L.) microveneers
- 2024
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Ingår i: Holzforschung. - : Walter de Gruyter. - 0018-3830 .- 1437-434X. ; 78:5, s. 283-292
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Tidskriftsartikel (refereegranskat)abstract
- Humins are heterogeneous and polydisperse furanic macromolecules derived from sugar biorefinery. Improving wood properties by humination has become of interest recently. This study examined the photodegradation stability of European pine sapwood microveneers modified with humins at different concentrations of citric acid (CA) and succinic acid (SA) as reaction catalysts, e.g., 1.5 %, 3 %, and 4.5 % wt.%. The photostability of huminated wood was assessed after 48 h, 96 h, and 144 h of exposure to the accelerated weathering test by means of mass loss and finite-span tensile strength. The results were compared with unmodified and also unweathered samples. The FT-IR spectroscopy showed apparent changes in the chemical structure of wood by humination modifications. The weight percentage gains of the samples increased with increasing the concentration of the catalyst. While no differences were observed between the samples after two weeks of the water leaching. The strength losses of weathered microveneers were, however, mostly reduced by humin-based formulas containing catalysts, where the microveneers modified with 1.5 % and 3 % CA showed respectively 32 % and 41 % lower strength loss values than the unmodified samples after 144 h of weathering. Overall, the results showed a high potential for humins to protect wood against photodegradation.
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| 14. |
- Ghorbanian Far, Mohammad, et al.
(författare)
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Physical and mechanical properties of different beech wood species grown at various climate conditions: a review
- 2024
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Ingår i: Holzforschung. - : Walter de Gruyter. - 0018-3830 .- 1437-434X.
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Forskningsöversikt (refereegranskat)abstract
- Beech wood, renowned for its diverse applications spanning construction, flooring, furniture, veneer, and plywood, holds a paramount position among industrial wood species. Nevertheless, the myriad of beech species worldwide, coupled with the dynamic impact of climate change, have produced structural variations within beech trees. Extensive research has scrutinized the physical and mechanical attributes of beech wood species across the globe. Findings reveal distinguishable mechanical strength, yet increased density leads to notable rates of shrinkage and swelling, somewhat constraining its utility in select domains. Identifying research gaps can create new efforts aimed at exploiting the potential of these wood resources. This paper outperforms a mere exploration of beech wood properties over the past two decades; it delves into the ramifications of climatic fluctuations, temperature shifts, wind dynamics, and soil composition. Given the lack of a comprehensive compendium documenting the full range of physical, mechanical, and microscopic attributes of the Fagus genus, this paper aims to compile information that integrates this multifaceted information.
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| 15. |
- Hackenstrass, Klara, et al.
(författare)
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Structure, flexibility and hydration properties of lignin dimers studied with Molecular Dynamics simulations
- 2024
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Ingår i: Holzforschung. - 1437-434X .- 0018-3830. ; 78:2, s. 98-108
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Tidskriftsartikel (refereegranskat)abstract
- Lignin is an abundant polymer found in wood and grasses, but due to its heterogeneity and complex macromolecular structure it has been less utilized than cellulose. While the building blocks are known, the way they are linked is less understood. Here, Molecular Dynamics simulations were used to systematically characterize seven linkages found in native lignin. Their influence on lignin and water structure, and their interactions were analyzed. The study is limited to guaiacyl (G-G) dimers connected by the following common softwood linkages; 5-5 ', 4-O-5 ' , alpha-O-4 ', beta-1 ', beta-5 ', beta-O-4 ' and beta-beta '. The simulations show that the linkage has a significant effect on conformational preference and lignin-water interaction. Especially, the behavior of the beta-O-4 ' shows unique properties, both in terms of conformational freedom and interaction with water. Within the beta-O-4 ' dimer, pi-pi stacking between the aromatic rings is possible. The molecule has two distinct common conformations, one compressed and one extended. These preferences also lead to a different effect of beta-O-4 ' dimer on the surrounding water, where water is found close to the linkage itself but expelled from the aromatic rings to a larger extent than the other linkages. These findings are important for lignin solubility as well as its depolymerization mechanisms.
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| 16. |
- Henrik-Klemens, Åke, et al.
(författare)
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An in situ Raman spectroscopic method for quantification of polyethylene glycol (PEG) in waterlogged archaeological wood
- 2020
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 74:11, s. 1043-1051
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Tidskriftsartikel (refereegranskat)abstract
- The weakened microstructure of archaeological wood (AW) objects from waterlogged environments necessitates consolidation to avoid anisotropic shrinkage upon drying. Polymer impregnation through submergence or spraying treatments is commonly applied, and for larger and thicker objects, the impregnation period can stretch over decades. Thus, for efficient treatment, continuous monitoring of the impregnation status is required. Today, such monitoring is often destructive and expensive, requiring segments for extraction and chromatographic quantification. This study proposes an in situ Raman spectroscopic method for quantification of polyethylene glycol (PEG) in waterlogged AW. A calibration model was built on standards of PEG, cellulose powder, and milled wood lignin using orthogonal partial least squares (OPLS). The OPLS model had a strong linear relationship, and the PEG content in wood of varying degrees of degradation could be determined. However, the accuracy of the model was low with a root mean square error of prediction of 11 wt%. The low accuracy was traced to the heterogeneity in the calibration and validation set samples with regard to the small probing volume of the confocal instrumental setup.
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| 17. |
- Henrik-Klemens, Åke, 1990, et al.
(författare)
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The glass transition temperature of isolated native, residual, and technical lignin
- 2024
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Ingår i: Holzforschung. - 1437-434X .- 0018-3830. ; 78:4, s. 216-230
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Tidskriftsartikel (refereegranskat)abstract
- The glass transition temperatures (T g) of native, residual, and technical lignins are important to lignocellulose pulping, pulp processing and side stream utilization; however, how the structural changes from native to residual and technical lignin influences T g has proven difficult to elucidate. Since the T g of macromolecules is greatly influenced by the molecular weight, low-molecular-weight fractions, such as milled wood lignin (MWL), are poor representatives of lignin in the cell wall. To circumvent this problem, lignins of both high yield and purity were isolated from Norway spruce and softwood kraft pulp using the enzymatic mild acidolysis lignin (EMAL) protocol. Technical softwood kraft lignin was also fractionated into groups of different molecular weights, to acquire lignin that spanned over a wide molecular-weight range. A powder sample holder for dynamic mechanical analysis (DMA), was used to determine the T g of lignins, for which calorimetric methods were not sensitive enough. The T gs of EMAL were found to be closer to their in situ counterparts than MWL.
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| 18. |
- Huč, Sabina, 1987-, et al.
(författare)
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Numerical analysis of moisture-induced strains and stresses in glued-laminated timber
- 2020
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Ingår i: Holzforschung. - : Walter de Gruyter. - 0018-3830 .- 1437-434X. ; 74:5, s. 445-457
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Tidskriftsartikel (refereegranskat)abstract
- Changes in relative humidity of the ambient air, RH (%), cause wetting and drying of wood material, which results in non-uniform moisture contents or moisture gradients, and consequently in moisture-induced stresses and strains in the glued-laminated timber (glulam) members. The aim of the present paper is to perform a hygromechanical analysis to predict the mechanical behavior of glulam specimens exposed to two RH regimes, causing wetting from 50% to 90% RH and drying from 90% to 50% RH, and compare the numerical to the experimental results. The aims are also to quantitatively analyze the influence of characteristic material parameters required in the multi-Fickian moisture transport model and the mechanical model on moisture-induced strains and stresses in glulam specimens and to determine the possibility of cracking of the material by analyzing the maximum tensile stresses perpendicular to the grain. Accurate numerical predictions of moisture contents and moisture-induced strains are obtained in the glulam specimens during wetting and drying as compared to the experimental results. The influence of a particular characteristic material parameter on moisture-induced strains and stresses is characterized as significant, but not crucial when a rough numerical estimation of the mechanical behavior of the glulam beam exposed to RH changes is required.
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| 19. |
- Jebrane, Mohamed
(författare)
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Upgrading the durability of perishable wood species using extractives from side streams of durable wood sawmill operations: a review
- 2023
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 77, s. 753-761
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Forskningsöversikt (refereegranskat)abstract
- Natural durability is one of the most rated features in wood end-use applications. In fact, several precious native tropical wood species produce timber of high natural durability, which is also related to long service life even for the highest hazard classes. However, selective logging is driving the existing volume of this group of species to near extinction. The remainder of the alternative species produces perishable timbers, which require synthetic chemical protection to prolong their service life but with detrimental effects on humans and the environment. Therefore, transferable durability has emerged as an alternative to gradually substitute traditional wood preservatives. From this approach, extractives from naturally durable wood species are removed and transferred to the non-durable wood species as an alternative environmental-friendly option for wood protection. Indeed, extractives from durable wood species have proven to have a deterrent effect on fungi, bacteria and termites and could be used to protect perishable wood species. Thus, this review aims to assess the prospects of developing environmentally friendly wood preservatives based on extractives sourced from highly natural, durable wood species to treat and add value to the group of perishable timbers. A step-wise analysis offers insights and challenges on (i) potential sources of extractives; (ii) effective extraction methods; (iii) extractive-based preservative formulation; and (iv) effective treatment methods for better preservative fixation for better wood protection. Accounts about the way forward for the development of extractive-based wood preservatives are also presented.
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| 20. |
- Joelsson, Tove, et al.
(författare)
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The impact of sulfonation and hot-pressing of low-energy high temperature chemi-thermomecanical pulp
- 2022
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Ingår i: Holzforschung. - : Walter de Gruyter. - 0018-3830 .- 1437-434X. ; 76:5, s. 463-472
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Tidskriftsartikel (refereegranskat)abstract
- Hot-pressing high yield pulp-based paper, well above softening temperature of lignin, increases paper density and paper strength. It has been investigated whether improved paper strength can be achieved and if lower pressing temperatures can be used in combination with increased sulfonation of HTCTMP (high temperature chemi-thermomechanical pulp).Moist paper sheets from low-energy Norway Spruce HTCTMP were hot-pressed up to 270°C. Sulfite charges from 25 to 120 kg/bdt were used during impregnation, preheating, and refining at 180°C with an electric energy demand of 370–500 kWh/bdt to a shive content of 1%. The pulps were mixed with 20% bleached unrefined kraft pulp to ensure that the sheet formation would not be hampered by the coarseness of the pulps. A tensile index of 70 kNm/kg was reached with highest sulfite dosage at only 150°C in pressing temperature which can be compared to 60 kNm/kg for the corresponding market CTMP. To obtain high wet strength, the highest temperature was required, while the sulfite charge was found to be of minor importance. This study has shown that it is possible to obtain strong and wet-stable paper products from HTCTMP, having a yield of 94-96% and a low energy demand at reduced pressing temperature.
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| 21. |
- Kron, Linus, 1996, et al.
(författare)
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A comparative study of the cell wall level delignification behaviour of four Nordic hardwoods during kraft pulping
- 2024
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Ingår i: Holzforschung. - 1437-434X .- 0018-3830. ; In Press
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Tidskriftsartikel (refereegranskat)abstract
- Wood is a heterogeneous material with significant variation among species. This inherent complexity poses a challenge to the continuous expansion of our understanding of the kraft process; yet previous pulping research has mainly been limited to a few species. This study investigates variations among some less studied species and their cell wall level delignification behaviour during kraft pulping. Ground wood of birch, beech, aspen, and alder were pulped at near-constant composition and temperature conditions. Minor, yet significant, differences in the rates of their delignification were observed: aspen had a pronounced fast rate during the initial stage, whereas alder delignified more slowly relative to its high initial lignin content. The dissolution of xylan was substantially faster for birch. In contrast, no substantial differences were detected between the species in the molecular weight and structure of the dissolved wood components, suggesting that the different delignification behaviours stem from variations in the residual phase. The molecular weight distribution of dissolved lignin was uniform during the initial stage of pulping, which is indicative of rapid and extensive fragmentation. Subsequently, the weight increased continuously for the remainder of the process, suggesting that the mass transfer within the cell wall influenced the overall delignification kinetics.
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| 22. |
- Kron, Linus, 1996, et al.
(författare)
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Kraft cooking of birch wood chips: Differences between the dissolved organic material in pore and bulk liquor
- 2023
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Ingår i: Holzforschung. - 1437-434X .- 0018-3830. ; 77:8, s. 598-609
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Tidskriftsartikel (refereegranskat)abstract
- The delignification of birch chips during kraft pulping was investigated, targeting both the impregnation and cooking steps. Wood chips were impregnated using white liquor, white liquor + NaCl, water or NaCl aqueous solution. Then, the chips were cooked in batch autoclaves applying the same constant composition cooking conditions for all samples. Pulp and two fractions of black liquor (bulk liquor and centrifuged liquor representing the liquor inside the wood chips and fibers) were collected after different pulping times and analyzed for lignin and carbohydrate content. The dissolved wood components were precipitated from selected samples and characterized with respect to composition, molecular weight distribution and structural motifs. Cooking chemicals in the impregnation liquors led to faster delignification and xylan removal during cooking. Higher contents of lignin and xylan were measured in the lumen than in the bulk. The concentration profiles also showed accumulation of dissolved material in the lumen over time, suggesting significant mass transport limitation from lumen to bulk. Further analysis revealed higher fragmentation/degradation of dissolved material with increasing pulping time and in the bulk when compared to the lumen liquor, as demonstrated by the lower molecular weights and the changes in chemical shifts in the NMR spectra.
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| 23. |
- Kwan, Isabella, et al.
(författare)
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Emulsions of cellulose oxalate from Norway spruce (Picea abies) bark and dissolving pulp
- 2023
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 77:7, s. 554-565
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Tidskriftsartikel (refereegranskat)abstract
- Tree bark is normally a side-stream product but by an integrated bark biorefinery approach, valuable compounds may be recovered and used to replace fossil-based products. Norway spruce bark was extracted to obtain cellulose, which was chemically treated to produce cellulose oxalate (COX) which was homogenized to yield nanocellulose. The nanocellulose was used to produce Pickering emulsions with almond oil and hexadecane as organic phases. COX from dissolving pulp was used to study the effect of various raw materials on the emulsifying properties. The COX samples of bark and dissolving pulp contained a significant amount of hemicelluloses, which affected the viscosity results. The emulsion properties were affected by the organic phases and the aspect ratio. Emulsions using hexadecane were more stable than the emulsions using almond oil. Since the aspect ratio of bark was lower than that of the dissolving pulp, the emulsifying properties of the COX dissolving pulp was better. It has been shown that nanocellulose from cellulose oxalate of both spruce bark and dissolving pulp is a promising substitute for petroleum-based emulsifiers and surfactants. By utilizing bark, value-added products can be produced which may be economically beneficial for various industries in the future and their aim for climate-neutral products.
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| 24. |
- Lindén, Pär A., et al.
(författare)
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Stabilising mannose using sodium dithionite at alkaline conditions
- 2020
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Ingår i: Holzforschung. - : Walter de Gruyter. - 0018-3830 .- 1437-434X. ; 74:2, s. 131-140
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Tidskriftsartikel (refereegranskat)abstract
- The kraft process remains the dominant-chemical pulping process but still struggles with extensive hemicellulose degradation. Such degradation has previously been mitigated through the use of anthraquinone; but due to it recently being found to have carcinogenic properties, anthraquinone is now being phased out. One alternative, sodium dithionite, was initially investigated in the 1950s but was found to be unviable. The present study investigated whether sodium dithionite could be made viable through the use of different processing parameters, using mannose as a model compound and measuring the yield of mannitol in the various systems using gas chromatography with flame ionization detection (GC-FID) and nuclear magnetic resonance (NMR). Alkalinity was found to be crucial; at pH 14 as well as pH 7, dithionite indeed proved unviable, but if pH was kept at either 8 or 10 significant reduction was seen to occur. The best results were obtained at pH 10 when a lower temperature (70 degrees C) was used to compensate for alkaline degradation of the mannose reactant.
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| 25. |
- Mai, Carsten, et al.
(författare)
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A brief overview on the development of wood research
- 2022
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Ingår i: Holzforschung. - : Walter de Gruyter. - 0018-3830 .- 1437-434X. ; 76:2, s. 102-119
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Tidskriftsartikel (refereegranskat)abstract
- Wood science covers in particular the areas of the formation and composition as well as the chemical, biological and physical-mechanical properties of wood. First comprehensive studies have already been published in the last century. Detailed knowledge of wood is required for the processing of wood, the production of wood-based materials, and the utilization of wood and wood-based materials as buildings and various other products such as furniture. This review gives a brief overview on the progress in wood chemistry, wood biology (including photosynthesis and biodeterioration), and physical-mechanical properties of wood and wood-based materials. These fundamentals are also essential for understanding technological processes and product development.
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| 26. |
- Marion de Godoy, Carolina, 1993, et al.
(författare)
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Kraft pulping of model wood chips: Local impact of process conditions on hardwood delignification and xylan retention
- 2024
-
Ingår i: Holzforschung. - 1437-434X .- 0018-3830. ; In Press
-
Tidskriftsartikel (refereegranskat)abstract
- Local evolution of delignification and xylan removal inside wood chips was investigated throughout the initial stages of kraft cooking. Model chips of birch sapwood were pulped at 145, 155 and 165 » °C, utilizing white liquors with hydroxide content ranging from 0.25 to 0.55 » mol/kg. The composition of different sections in each cooked sample was then determined. Xylan was isolated from selected samples and analyzed using size exclusion chromatography and HSQC NMR. Most changes in concentration and structure of residual xylan occurred early in the process (<45 » min). Furthermore, xylan samples isolated from the tissue of different cooked chips had similar average molecular weights, indicating that temperature and alkali content had little impact over the extent of reactions affecting residual xylan. In contrast, xylan dissolution was significantly dependent on pulping conditions, increasing with hydroxide concentration. The lignin profile inside the cooked chips also varied with alkali content and temperature, and it was shown to be more uniform when applying low cooking temperatures (145 » °C). Finally, increased delignification and xylan removal were detected close to the transverse surfaces of chips (likely due to the fast mass transport in vessels/lumen), implying that anatomical features of wood can have a significant impact on pulping.
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| 27. |
- Martinsson, Axel, 1992, et al.
(författare)
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The influence of transition metal ions on the oxidation of kraft pulp using hydrogen peroxide under mildly acidic conditions
- 2023
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 1437-434X .- 0018-3830. ; 77:5, s. 318-325
-
Tidskriftsartikel (refereegranskat)abstract
- Oxidation of kraft pulp using hydrogen peroxide under mild acidic conditions can be applied in order to obtain new functionality of the fibres, in the form of carbonyl groups. The hydrogen peroxide concentration must, however, be higher than consumed by the oxidation reactions meaning that the liquid must be recirculated to fully utilize the hydrogen peroxide. This paper investigates the consequences of recirculation of the oxidation liquor. It was found that recirculation results in an accumulation of ions of transition metals (copper, iron and manganese) in the oxidation liquor. The transition metal ions are known for catalytic decomposition of hydrogen peroxide, producing radicals which may react with carbohydrates, forming carbonyl groups as well as causing carbohydrate degradation. This was confirmed through the recirculation of oxidation liquor as well as through controlled addition of transition metals. At high transition metal ion concentration the reactions were fast and a severe degradation of carbohydrates was observed, accompanied by a rapid hydrogen peroxide consumption. The consequence of this, in an industrial context, is that the concentration of metal ions must be carefully controlled in order to add functionality to the cellulose without causing excessive degradation of carbohydrates or consumption of hydrogen peroxide.
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| 28. |
- Mäkelä, Mikko
(författare)
-
Improvement of interfacial interaction in impregnated wood via grafting methyl methacrylate onto wood cell walls
- 2020
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 74, s. 967-977
-
Tidskriftsartikel (refereegranskat)abstract
- Improving the interaction between the wood cell wall and a modifying agent is fundamental to enhancing the efficacy of wood modification. The extent of interaction is, nevertheless, difficult to evaluate due to the highly heterogeneous nature of the modified wood. In this study, methacryl groups were grafted onto the wood cell wall polymers, via the reaction between 2-isocyanatoethyl methacrylate (IEMA) and hydroxyl groups, to improve their compatibility and reactivity. Subsequently, methyl methacrylate (MMA) was introduced into methacrylated wood and copolymerized with the bonded methacryl groups. The distribution of IEMA and poly MMA (PMMA) in the wood cell walls was investigated by scanning electron microscopy (SEM) and confocal Raman microscopy. The results showed that MMA penetrated the wood cell walls and formed strong interfacial interaction, which was confirmed by confocal Raman microscopy combined with principal component analysis (PCA). With copolymerization, the highest anti-swelling efficiency (ASE) (57%) was achieved, because of the effect of methacrylation. Compared to the reference, the water resistance and hardness were significantly improved. In addition, the dynamic wettability was also altered largely due to copolymerization.
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| 29. |
- Neyses, Benedikt, 1986-, et al.
(författare)
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In-situ penetration of ionic liquids during surface densification of Scots pine
- 2021
-
Ingår i: Holzforschung. - : Walter de Gruyter. - 0018-3830 .- 1437-434X. ; 75:6, s. 555-562
-
Tidskriftsartikel (refereegranskat)abstract
- The moisture-induced recovery of compressed wood is one of the major problems of wood densification technology. Achieving a cost-efficient surface densification process without the need for additional resins to eliminate the set-recovery may lead to an increase in value of low-density wood species. A previous study has shown that a pre-treatment with ionic liquids (ILs) can nearly eliminate the set-recovery. It was however observed that during the pre-treatment process the IL did not penetrate sufficiently deep into the wood to explain the achieved reduction in set-recovery. Based on these findings, the hypothesis was posed that further penetration of the IL into the wood occurs during the densification stage as a consequence of the applied heat and pressure. Thermo-gravimetric analysis (TGA) and gas-chromatography mass-selective-detection (GC-MSD) showed that the depth of penetration of the IL was greater after the densification process than before. Digital image correlation (DIC) showed that in regions with a high IL concentration, there was almost no set-recovery, and it gradually increased with a decrease in the IL concentration, as observed with TGA and GC-MSD analysis.
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| 30. |
- Neyses, Benedikt, 1986-, et al.
(författare)
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The effect of ionic liquid and superbase pre-treatment on the spring-back, set-recovery and Brinell hardness of surface-densified Scots pine
- 2020
-
Ingår i: Holzforschung. - : Walter de Gruyter. - 0018-3830 .- 1437-434X. ; 74:3, s. 303-312
-
Tidskriftsartikel (refereegranskat)abstract
- Compressing the surface of sawn timber results in a substantial increase in hardness, and this opens up new market opportunities of using low-density timber species as the raw material for high-value wood products. Unfortunately, widespread commercialisation is hindered by the lack of an industrially viable surface densification process, the major obstacle being the set-recovery (SR) of the densified wood cells upon exposure to moisture. Our hypothesis is that partial dissolution of the crystalline cellulose during densification will largely prevent the SR of densified wood. We therefore evaluated the effect of ionic liquid (IL) or organic superbase pre-treatment on the elastic spring-back (SB), SR and Brinell hardness (HB) of surface-densified wood. Specimens of Scots pine were treated with solutions of ILs or superbases, and then densified in a hot press at temperatures between 200°C and 270°C. The SR was reduced from 90% for the control group to only about 10% for the treated materials. The treated and densified specimens exhibited a higher HB than their untreated and densified counterparts. The method presented in this study is a precursor to the development of a continuous densification process adapted for an open system. Further studies are needed to understand the underlying mechanisms of the pre-treatment.
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| 31. |
- Pedersen, Nanna Bjerregaard, et al.
(författare)
-
Correlation between bacterial decay and chemical changes in waterlogged archaeological wood analysed by light microscopy and Py-GC/MS
- 2021
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 75:7, s. 635-45
-
Tidskriftsartikel (refereegranskat)abstract
- © 2020 Nanna Bjerregaard Pedersen et al., published by De Gruyter, Berlin/Boston 2020. Erosion bacteria are the main degraders of archaeological wood excavated from waterlogged environments. Light microscopy and analytical pyrolysis coupled with gas chromatography/mass spectrometry (Py-GC/MS) were exploited to study waterlogged archaeological wood (Pinus sylvestris L.) at different stages of bacterial decay. The research explored the biochemical changes related to erosion bacteria degradation of the secondary cell wall in the wood cells and the chemical changes related to abiotic processes induced by the long-term waterlogged burial environment. Erosion bacteria were demonstrated by chemical analysis to cause significant holocellulose depletion. Detailed analysis of the holocellulose and lignin pyrolysis products revealed only minor chemical changes in the residual structure even after heavy erosion bacteria decay. Chemical changes in the lignin polymer is associated to enzymatic unlocking of the lignocellulose to gain access to the holocellulose fraction of the cell wall. Chemical changes in the holocellulose fraction are suggested to stem from depolymerisation and from alterations in the polymer matrix of the residual wood cell wall structure. Interestingly, a difference was observed between the sound reference wood and the waterlogged archaeological wood without erosion bacteria decay, indicating that long-term exposure in waterlogged environments results in partial decay of the holocellulose even in absence of bacterial activity.
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| 32. |
- Ringman, Rebecka, et al.
(författare)
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Brown rot gene expression and regulation in acetylated and furfurylated wood : A complex picture
- 2020
-
Ingår i: Holzforschung. - : De Gruyter. - 0018-3830 .- 1437-434X. ; 74:4, s. 391-399
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to investigate Rhodonia placenta expression patterns of genes involved in the depolymerisation during the non-enzymatic phase in acetylated (WAc) and furfurylated wood (WFA). During the 98-day-long exposure, WAc [22.6% weight per cent gain (WPG) on average] and WFA (69% WPG on average) lost no more than 3% mass while the untreated wood (WUn) reached 41% mass loss (ML) in 55 days. Expression of six genes putatively involved in the non-enzymatic degradation process were investigated. In conclusion, expression levels of alcohol oxidase Ppl118723 (AlOx1) and laccase Ppl111314 (Lac) were significantly higher in the modified wood materials (WMod) than in WUn, which is in accordance with previous results and may be explained by the absence of the degradation products that have been proposed to down-regulate the non-enzymatic degradation process. However, copper radical oxidase Ppl156703 (CRO1) and a putative quinate transporter Ppl44553 (PQT) were expressed at significantly lower levels in WMod than in WUn while quinone reductase Ppl124517 (QRD) and glucose oxidase Ppl108489 (GOx) were expressed at similar levels as in WUn. These results suggest that gene regulation in WMod is more complex than a general up-regulation of genes involved in the non-enzymatic degradation phase.
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| 33. |
- Salmén, Lennart
(författare)
-
Celebrating 75 years of Holzforschung
- 2022
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 76:2, s. 101-101
-
Tidskriftsartikel (refereegranskat)
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| 34. |
- Sandberg, Christer, 1962-
(författare)
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Fibre development in an intensified mechanical pulping process
- 2021
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 75:9, s. 824-837
-
Tidskriftsartikel (refereegranskat)abstract
- Mechanical pulp for printing paper can be produced with a process that involve much less equipment and that require much lower specific energy compared to conventional processes. Even though common evaluation methods, e.g. handsheet testing, have shown that the pulp quality is similar for the simplified and the conventional processes, it is not known how fibre properties, at the microscopic level, is developed with the simplified process. In this mill scale study, the fibre properties attained with an "intensified"mechanical pulping process, consisting of single stage high consistency double disc refining followed by two stage low consistency refining and no reject treatment was investigated. The simplified process was compared to a process with a reject system. The simplified process rendered fibres with higher degree of fibrillation, higher share of axial splits, lower fibre wall thickness but slightly lower length than the conventional process. The fibrillar fines size distribution of the two processes was different. The conventional process generated more of small fibrillar fines which probably explains the higher tensile index at given density for that process. The results show that it is possible to simplify the production process for mechanical pulp and reduce the specific energy with over 700 kWh/adt.
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| 35. |
- Scharf, Alexander, 1990-, et al.
(författare)
-
Hardness of surface-densified wood. Part 1: material or product property?
- 2022
-
Ingår i: Holzforschung. - : Walter de Gruyter. - 0018-3830 .- 1437-434X. ; 76:6, s. 503-514
-
Tidskriftsartikel (refereegranskat)abstract
- The established methods for testing the hardness of wood are of questionable value for assessing the performance of surface-densified wood, since the density profile beneath the densified surface is an important property that needs to be considered. The purpose of this study was to evaluate the influence of the density profile of surface-densified wood and the hardness test parameters, such as indenter geometry and applied load on the measured hardness. The influence of the density profile varied considerably depending on the hardness test parameters. This can make a comparison of hardness values of surface-densified wood prone to misinterpretation. The selection of hardness test parameters should either be product-specific, or the density profile itself should be used to evaluate the hardness of surface-densified wood. A strong influence of the density profile on the indentation depth development during the hardness tests indicates the possibility of predicting the density profile based on the hardness test methods.
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| 36. |
- Scharf, Alexander, 1990-, et al.
(författare)
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Hardness of surface-densified wood. Part 2: prediction of the density profile by hardness measurements
- 2022
-
Ingår i: Holzforschung. - : Walter de Gruyter. - 0018-3830 .- 1437-434X. ; 76:6, s. 515-524
-
Tidskriftsartikel (refereegranskat)abstract
- The density profile of surface-densified wood has a major influence on the indentation resistance of the material. A method that can predict the density profile in surface-densified wood from measurements of the indentation in a hardness test was established. The combined information of hardness and density profile is expected to better assess the performance of surface-densified wood. Density profile and hardness test data for surface-densified Scots pine have been subjected to a partial least squares analysis to determine the relationship between the indentation depth measured during a hardness test and the density profile measured by X-ray densitometry. Among seven different hardness tests, which varied in test force and indenter geometry, the Brinell method according to the EN 1534 standard showed the highest correlation between the indentation-versus-time curve and the density profile. The mean absolute error for the prediction of density profiles in an external test set was 5–10%, indicating that the method proposed in this study can be used to replace X-ray densitometry in process control and process design.
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| 37. |
- Scharf, Alexander, 1990-, et al.
(författare)
-
The effect of the growth ring orientation on spring-back and set-recovery in surface-densified wood
- 2023
-
Ingår i: Holzforschung. - : Walter de Gruyter. - 0018-3830 .- 1437-434X. ; 77:6, s. 394-406
-
Tidskriftsartikel (refereegranskat)abstract
- Wood under thermo-mechanical densification behaves differently depending on the cross-sectional growth ring orientation (GRO) relative to the direction of compression. This influences the degree of cell damage, but also the shape-memory effects occurring when the compression load is released (spring-back) and when the timber is re-moistened (set-recovery). To study how the GRO influences the shape-memory effects, Scots pine specimens were separated into three distinct groups of GRO (Flat, Inclined, Hybrid) and then thermo-mechanically surface-densified. Spring-back and set-recovery were determined by thickness measurements and by digital image correlation. A GRO parallel to the densified surface, resulted in a low spring-back and a high set-recovery which were uniform over the width of the specimen. Specimens with a GRO between 15 and 45° to the densified surface showed high spring-back and low set-recovery, indicating cell-wall damage. Spring-back mainly occurred in the non-plasticised region immediately below the heated surface region and elasto-plastic rolling-shear deformation along individual growth rings occurred. The GRO of softwood subjected to thermo-mechanical densification determines if an applied load results in rolling shear-deformation or radial compression. This in turn determines where in the cross-section and when in the process the cells deform and if this deformation occurs below or above the glass-transition temperature.
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| 38. |
- Starrsjö, Sara, et al.
(författare)
-
Reduction of adsorbable organically bound halogens (AOX) formation at near-neutral pH chlorine dioxide bleaching of softwood kraft pulp
- 2020
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 74:6, s. 597-604
-
Tidskriftsartikel (refereegranskat)abstract
- Recently, a new type of bleaching sequence, Elemental Chlorine Free (ECF) light with one D stage, has been developed. It combines the efficiency and high selectivity of chlorine dioxide (ClO2) bleaching with more environmental friendly oxygen based bleaching chemicals. This work examines the effect of pH on the formation of adsorbable organically bound halogens (AOX) in an intermediate D stage - a single ClO2 stage at the middle of an ECF light bleaching sequence. Carbon dioxide (CO2) is used to generate a bicarbonate buffer in situ, stabilizing the pH during the bleaching. Near-neutral pH is hypothesized to decrease the formation of strongly chlorinating species, so that the AOX formation is reduced. The results indicate that a near-neutral pH D stage can reduce the AOX content in the effluents with up to 30%. The ISO brightness was unchanged to a lower ClO2 consumption. The pulp viscosity was slightly higher after near-neutral pH D stage, but to its disadvantage a lesser delignification and removal of HexA was obtained. The degradation of HexA correlated well with the AOX, affirming earlier theories that HexA has a major impact on the AOX formation. The higher amounts of residual HexA and lignin resulted in more thermal yellowing of the pulps bleached with a near-neutral pH D stage.
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| 39. |
- Terziev, Nasko
(författare)
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A model to predict the kinetics of mass loss in wood during thermo-vacuum modification
- 2021
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 75, s. 474-479
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Tidskriftsartikel (refereegranskat)abstract
- Mass loss (ML) of wood caused by thermal degradation is one of the most important features of the thermal treatments and referred to as an indicator of intensity and quality of the process. The ML is proportional to the quantity of the effective heat power exchanged during the treatment process, represented by the area of the temperature profile versus time during the process. In this paper a model for the ML prediction based on the relative area was discussed. The model proposed an analytical solution to take into account the non-linear trend of ML when plotted versus temperature and time as observed in isothermal experiments. The model was validated comparing calculated and measured final ML of samples treated during thermal modification tests with different temperature profiles. The results showed that the relative area calculated in a transformed time-temperature space improves the correlation with the measured ML.
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| 40. |
- Terziev, Nasko
(författare)
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Decay, insect, and termite resistance of wood modified with epoxidized vegetable oils
- 2021
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 75, s. 281–287-
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Tidskriftsartikel (refereegranskat)abstract
- Samples of Scots pine sapwood were treated with epoxidized linseed and soybean oils to improve decay, insect and termite resistance of wood. Non-epoxidized (raw) linseed and soybean oils were included as reference treatment in the study. In the epoxidation process, hydrogen peroxide was used to open double bounds, and acetic acid was added as a catalyst. Two retention levels, Ret A (80–140 kg m−3) and Ret B (170–270 kg m−3), two impregnation methods (full cell and empty cell) and emulsion technique were used. Samples treated with epoxidized oils had significantly lower mass losses than untreated samples while epoxidized oils showed higher mass losses than unepoxidized oils for Coniophora puteana and Trametes versicolor according to EN 113 for decay test. By adding boron, fungicidal properties were introduced to the treatment. All the vegetable oils showed 100% the mortality rate against larvae of Hylotrupes bajulusaccording to EN 47. Moreover, leached wood samples treated with oils also showed 100% larvae mortality. Additionally, termite testing based on EN 117 revealed 100% Reticulitermes lucifugus mortality for all leached oil treated samples.
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| 41. |
- Van Niekerk, Philip B., et al.
(författare)
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Mapping the biotic degradation hazard of wood in Europe - Biophysical background, engineering applications, and climate change-induced prospects
- 2022
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 76:2, s. 188-210
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Tidskriftsartikel (refereegranskat)abstract
- Construction using timber has seen a resurgence in light of global climate mitigation policies. Wood is a renewable resource, and engineered wood products are proving to be competitive against concrete and steel while having several advantages. However, while the renewable nature of wood in construction is a beneficial property for climate mitigation policies, the process of biodegradation introduces a challenge for service life planning. A review of hazard mapping is presented while developing contemporary hazard maps, occurrence maps and projected hazard maps for 2050 using representative concentration pathways (RCP) 2.6 and 8.5. The risk of timber decay is expected to increase in most of Europe as the temperatures rise, with a decrease expected in dryer regions. Termites are likely to experience a range expansion as more areas become suitable, while human activity and an increase in extreme weather events like floods are expected to facilitate dispersion. Marine borer species already present a risk in most European coastal regions; however, the effect of changes in water temperatures are likely to shift the boundaries for individual borer species. Overall, warmer climates are expected to increase the metabolic activity of all of these organisms leading to a general reduction in service life.
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| 42. |
- Vaziri, Mojgan, et al.
(författare)
-
Parameter estimation and model selection for water vapour sorption of welded bond-line of European beech and Scots pine
- 2023
-
Ingår i: Holzforschung. - : Walter De Gruyter. - 0018-3830 .- 1437-434X. ; 77:7, s. 515-526
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Tidskriftsartikel (refereegranskat)abstract
- The single exponential kinetics (SEK) and parallel exponential kinetics (PEK) models were fitted to kinetic sorption data of welded and unwelded Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.). Furthermore, diffusion coefficients of water vapour in wood were determined using two different Fickian diffusion solutions. The objective was to identify how well these models could represent the moisture contents of the specimens and to characterize differences between the sorption behaviour of welded and unwelded wood. This knowledge can be used to enhance the moisture resistance of welded wood, develop drying schedules, and improve the quality of timbers. The PEK and SEK models provided the most precise and the second most precise fits to the sorption kinetic data, respectively. The two Fickian models are equivalent when both the infinite series are truncated at n = 10. The Fickian models also exhibited the highest discrepancy with the experimental data. Nevertheless, the Fickian models fit relatively better to the sorption data of the welded wood than to that of the unwelded wood. This behaviour may be due to the rigid and less-swelling structure of the welded bond line.
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| 43. |
- Vaziri, Mojgan, et al.
(författare)
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Wettability of welded wood-joints investigated by the Wilhelmy method : part 1. Determination of apparent contact angles, swelling, and water sorption.
- 2021
-
Ingår i: Holzforschung. - : De Gruyter Open. - 0018-3830 .- 1437-434X. ; 75:1, s. 65-74
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Tidskriftsartikel (refereegranskat)abstract
- This study presents a novel application of the Wilhelmy plate method on welded joints of Scots pine sapwood and beech. Welding resulted in an increase in the contact angle (increased hydrophobicity) as well as a decrease in the water uptake and swelling of the welded pine-joint compared to non-welded pine. When the welding time was extended from 4 to 5 s, these properties were further pronounced. Welding of beech, on the other hand, led to an increase in the contact angle and a decrease in the water uptake, but an increase in the swelling.Fourier Transform Infrared spectroscopy showed that welding increased the aliphatic C-H and unsaturated C=C stretching absorption bands in pine and beech. Scanning electron microscopy showed a dense structure at the welded joints of the both species, giving evidence of a lower porosity that leads to a lower permeability as a result of the welding.
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| 44. |
- Vaziri, Mojgan, et al.
(författare)
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Wettability of welded wood-joints investigated by the Wilhelmy method : Part 2. Effect of wollastonite additive
- 2020
-
Ingår i: Holzforschung. - : De Gruyter. - 0018-3830 .- 1437-434X. ; 75:1
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Tidskriftsartikel (refereegranskat)abstract
- The effect of wollastonite on the wetting properties of welded Scots pine-joints was studied using the multicycle Wilhelmy plate method and by observation of the chemical composition of the welded joints. Welding pine with wollastonite for 5 s resulted in a decrease in the water uptake and the swelling, and an increase in the contact angle of the welded joint compared to welded wood without wollastonite. High-performance liquid chromatography and gas chromatography/mass spectrometry showed the presence of dehydration products such as furfural, 5-hydroxymethylfurfural, and levoglucosan in methanol extracts from welded joints of specimens welded with and without wollastonite. Phenols were also found by analysis using the Folin-Ciocalteu method and High-performance liquid chromatography. The importance of such compounds in relation to the wetting properties of the welded joint is discussed.
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| 45. |
- Wang, Miao, et al.
(författare)
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From hollow lignin microsphere preparation to simultaneous preparation of urea encapsulation for controlled release using industrial kraft lignin via slow and exhaustive acetone-water evaporation
- 2020
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Ingår i: Holzforschung. - : De Gruyter. - 0018-3830 .- 1437-434X. ; 74:1, s. 77-87
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Tidskriftsartikel (refereegranskat)abstract
- Lignin nano/microparticles have recently attracted growing interest for various value-additive applications of lignin, especially encapsulation. In this study, in order to establish a highly efficient and highly productive preparation process to effectively utilize technical lignin, a brand-new, slow and exhaustive solution evaporation process following a simple, self-assembly principle was developed using industrial softwood kraft lignin (SKL) from a starting acetone-water (80/20, v/v) solution to recover 100% of the lignin as homogeneous and well-shaped microspheres. The prepared microspheres had a typical average diameter of 0.81 ± 0.15 μm and were hollow with very thin shells (of nanoscale thickness). Based on this developed technique, encapsulation of urea by these lignin microspheres was directly achieved using the same process as hollow lignin microspheres with urea attached to the outside and entrapped inside of the wall. Two distinct urea release rates were observed for the urea-encapsulated microspheres: a fast release of the urea outside the shell wall and a slow (controlled) release of the urea inside the shell wall. The encapsulation efficiency was as high as 46% of the trapped urea as encapsulated inside the lignin microspheres. The slow and exhaustive solution evaporation procedure reported here is a simple and straightforward method for the valorization of industrial kraft lignin as hollow microspheres with controllable, homogeneous and desired morphologies, and especially for the direct preparation of lignin-based encapsulating fertilizers for controlled release.
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| 46. |
- Yin, Haiyan, et al.
(författare)
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Non-fluorine surface modification of acetylated birch for improved water repellence
- 2021
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Ingår i: Holzforschung. - : Walter de Gruyter. - 0018-3830 .- 1437-434X. ; 75:9, s. 857-868
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Tidskriftsartikel (refereegranskat)abstract
- In this work, a non-fluorinated surface treatment, i.e., hydrophobized silicone nanofilaments, was applied on both birch and acetylated birch wood samples via a gas-phase based reaction. A superhydrophobic behavior was observed on both the surface-modified samples as revealed by the static water contact angles (CAs) greater than 160°, also valid for samples prepared with the shortest reaction time of 1 h. The dynamic wettability behavior of the samples was studied by a multicycle Wilhelmy plate method. The surface-modified acetylated birch exhibited a pronounced enhanced water resistance, resulting in very low water uptake of 3 ± 1 wt% after 100 cycles, which was not only about 29 and 5 times lower than that of the non-surface-modified birch and acetylated birch, respectively, but also three times lower than that of the surface-modified birch. Moreover, the aesthetic appearance of the acetylated wood was maintained as the surface modification only resulted in a small color change. This work shows the potential of preparing super water-repellent wood by non-fluorinated surface modification.
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| 47. |
- Vaziri, Mojgan, et al.
(författare)
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Water-vapour sorption of welded bond-line of European beech and Scots pine
- 2023
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Ingår i: Holzforschung. - : De Gruyter. - 1437-434X. ; 77:7, s. 500-514
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Tidskriftsartikel (refereegranskat)abstract
- The wood–water interactions of welded bond-lines of European beech (Fagus sylvatica L.) and Scots pine (Pinus sylvestris L.) were in this paper studied for the first time with dynamic vapour sorption equipment. The aim of this study was to characterize the water sorption in the welded bond-line and to define to which extent it deviates from water sorption of the unwelded wood. The objective was to provide deepened knowledge about water sorption of the welded bond-line, which could be used to improve the moisture resistance of welded wood in the future. The welded wood generally had lower equilibrium moisture contents than the unwelded wood. The welded bond-lines of beech and pine showed greater hysteresis than the unwelded wood from 0 to 55 % relative humidity. All specimens showed faster adsorption than desorption. However, the welded wood showed slower adsorption but faster desorption than unwelded wood. The time to complete half of the fractional change in moisture content (E(t) = 0.5) increased as the moisture content increased. The adsorption diffusion coefficients of beech and welded beech were higher than those of pine and welded pine up to 50 % and 40 % RH, respectively. In desorption, pine had a higher diffusion coefficient than beech in the whole range of 85–0 % RH. Analogously, welded pine had a higher diffusion coefficient than welded beech in the range of 85–5 % RH. In contrast to the desorption, the welded wood always had lower adsorption diffusion coefficients than the corresponding unwelded wood. The diffusion coefficients showed irregular patterns in some ranges of the RH. Therefore, it was hard to make a clear conclusion about the water-sorption behaviour of the specimens based on the defined diffusion coefficients.
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