| 1. |
- Antonsson, Stefan, 1979-
(författare)
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Strategies for improving kraftliner pulp properties
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A large part of the world paper manufacturing consists of production of corrugated board components, kraftliner and fluting, that are used in many different types of corrugated boxes. Because these boxes are stored and transported, they are often subjected to changes in relative humidity. These changes together with mechanical loads will increase the deformation of the boxes compared to the case where the same loads are applied in a static environment. This enlarged creep due to the changes in relative humidity is called mechano-sorptive or accelerated creep. Mechano-sorptive creep forces producers to use high safety factors when designing boxes, and therefore, this is one of the key properties of kraftliner boards. Different strategies to decrease mechano-sorptive creep, and to simultaneously gain more knowledge about the causes for this phenomenon in paper, are the aim of this work. Derivatised and underivatised black liquor lignins, a by-product produced in pulp mills in large quantities, have been used together with biomimetic methods, to modify the properties of kraftliner pulp. Furthermore, the properties of kraftliner pulp have been compared to other pulps in order to evaluate the influence of fibre morphological factors, such as fibre width and shape factor, on the mechano-sorptive creep. In addition the influence of the chemical composition of the kraftliner pulp has been evaluated both by means of treating a kraftliner pulp with chlorite and xylanase and by producing pulps with different chemical composition. By using lignin and biomimetic methods, to create radical coupling reactions, it has been shown that it is possible to increase the wet strength of kraftliner pulp sheets. This method of treating the pulp showed, however, no significant effects on the mechano-sorptive creep. The addition of an apolar suberin-like lignin derivative, which has been shown to be possible to produce from natural resources, did show a positive effect on mechano-sorptive creep properties, but at the expense of stiffness properties in constant climate. Different pulps were compared with a kraftliner pulp and it was observed that the ratio between tensile stiffness and hygroexpansion can be used to estimate the mechano-sorptive creep properties. The hardwood kraft pulps investigated had lower hygroexpansion, probably due to more slender and straighter fibres, and higher tensile stiffness, probably due to lower lignin content. As the lignin content was varied by different methods in kraft pulps, it was observed that increased lignin content gives an increased hygroexpansion and decreased tensile stiffness as well as an increased mechano-sorptive creep. There were also indications of increased mechano-sorptive creep due to higher xylan content.
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| 2. |
- Wang, Yan
(författare)
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Pretreatment and Enzymatic Treatment of Spruce : A functional designed wood components separation for a future biorefinery
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The three main components of wood, namely, cellulose, hemicellulose, and lignin, can be used in various areas. However, since lignin covalently crosslinks with wood polysaccharides creating networks that is an obstacle for extraction, direct extraction of different wood components in high yield is not an easy matter. One potential approach to overcome such obstacles is to treat the wood with specific enzymes that degrade the networks by specific catalysis. However, the structure of wood is so compact that the penetration of the wood fibers by large enzyme molecules is hindered. Thus, the pretreatment of wood prior to the application of enzymes is necessary, for “opening” the structure.One pretreatment method that was performed in this thesis is based on kraft pulping, which is a well-established and industrialized technique. For untreated wood, the wood fibers cannot be attacked by the enzymes. A relatively mild pretreatment was sufficient for wood polysaccharides hydrolyzed by a culture filtrate. A methanol-alkali mixture extraction was subsequently applied to the samples that were pretreated with two types of hemicellulases, Gamanase and Pulpzyme HC, respectively. The extraction yield increased after enzymatic treatment, and the polymers that were extracted from monocomponent enzyme-treated wood had a higher degree of polymerization. Experiments with in vitro prepared lignin polysaccharide networks suggested that the increased extraction was due to the enzymatic untying. However, the relatively large loss of hemicellulose, particularly including (galacto)glucomannan (GGM), represents a problem with this technique. To improve the carbohydrate yield, sodium borohydride (NaBH4), polysulfide and anthraquinone were used, which increased the yields from 76.6% to 89.6%, 81.3% and 80.0%, respectively, after extended impregnation (EI). The additives also increased the extraction yield from approximately 9 to 12% w/w wood. Gamanase treatment prior to the extraction increased the extraction yield to 14% w/w wood.Sodium dithionite (Na2S2O4) is an alternative reducing agent for the preservation of hemicelluloses because it is less expensive than metal hydrides and only contains sodium and sulfur, which will not introduce new elements to the recovery system. Moreover, Na2S2O4has the potential to be generated from black liquor. Na2S2O4 has some preservation effect on hemicelluloses, and the presence of Na2S2O4 also contributed to delignification. The extraction yield increased to approximately 15% w/w wood. Furthermore, Na2S2O4 has been applied in the kraft pulping process of spruce. The yield and viscosity increased, while the Klason lignin content and kappa number decreased, which represents a beneficial characteristic for kraft pulp. The brightness and tensile strength of the resulting sheets also improved. However, the direct addition of Na2S2O4 to white liquor led to greater reject content. This problem was solved by pre-impregnation with Na2S2O4 and/or mild steam explosion (STEX) prior to the kraft pulping process. Following Na2S2O4 pre-impregnation and mild STEX, the obtained kraft pulp had substantially better properties compared with the properties exhibited after direct addition of Na2S2O4 to the white liquor.The wood structure opening efficiency of mild STEX alone was also tested. The accessibility of the wood structure to enzymes was obtained even at very modest STEX conditions, according to a reducing sugar analysis, and was not observed in untreated wood chips, which were used as a reference. The mechanical effect of STEX appears to be of great importance at lower temperatures, and both chemical and mechanical effects occur at higher STEX temperatures.
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| 3. |
- White, Jai, 1991-
(författare)
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From Facets to Flow: The Electrooxidation of Glycerol on Pd-based catalysts
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Glycerol, a by-product of biodiesel refineries, has uses in industries such as cosmetics, food, and pharmaceuticals. However, its usage is small compared to the amount of glycerol produced from biodiesel production. Therefore, there is an opportunity to use glycerol, an important platform chemical, as a cheap feedstock for the synthesis of valuable chemicals. These chemicals can be formed in aqueous media through the glycerol electrooxidation reaction (GEOR) on the anode with hydrogen gas concurrently generated on the cathode. This thesis focuses on the GEOR in alkaline media on Pd and PdNi catalysts. The works compiled here evaluate the GEOR using electrochemical methods such as cyclic voltammetry, galvanostatic polarisation curves, chronoamperometry and chronopotentiometry. Pd and PdNi catalysts were fabricated through chemical synthesis, and electrodeposition onto Ni substrates. Singularly oriented Pd crystal facets were studied, showing those approximating Pd (111) as the most active. Similarly faceted bimetallic PdNi nanoparticles proved significantly more active than pure Pd. Effects of mass transport, studied for Pd/NiRDE and PdNi/NiRDE, indicated performance effects linked to diffusion and underutilisation of thicker catalyst layers. In aerated solutions, industrially relevant current densities were achieved on PdNi/Nifoam in concentrated electrolytes at elevated temperatures for extended periods. The analysis of glycerol oxidation products, formed during steady state measurements, was done using high performance liquid chromatography. The two major products were consistently shown to be glycerate and lactate. This work, covering many aspects of the GEOR, shows that Pd-based catalysts have potential for future industrial application.
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| 4. |
- Magnusson, Hans, 1943-
(författare)
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From recovery boiler to integration of a textile fiber plant : Combination of mass balance analysis and chemical engineering
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Modern chemical technology is an efficient tool for solving problems, particularly within the complex environment of the pulp and paper industry, and the combination of experimental studies, mill data and mass balance calculations are of fundamental importance to the development of the industry. In this study various examples are presented, whereby chemical technology is of fundamental importance.It is well documented that under normal conditions the molten salt mixture from the kraft recovery boiler flows down into the dissolving tank without problems. However, in the case of alternatives to the kraft recovery boiler, knowledge of more precise data of the molten salts is required for the design calculations. In this study the viscosity for the case of sodium carbonate and 30 mole% sulphide has been measured and is of the magnitude 2 – 3 cP at temperatures relevant for a recovery boiler, i.e. similar to water at room temperature.The presence of non-process elements (NPE) in a typical pulp mill has been investigated. The main input is with regards to the wood, and anticipated problems include; deposits in evaporators, high dead-load in liquor streams, plugging of the upper part of the recovery boiler and decreasing efficiency in the causticization department. Efficient green liquor clarification is of the greatest importance as an efficient kidney for many NPE. Mill data and calculations show that the magnesium added in the oxygen delignification does not form a closed loop.Integration of a prehydrolysis kraft pulp mill producing dissolving pulp with a plant producing viscose textile fiber could be highly beneficial. The prehydrolysis liquor will contain both sugars and acetic acid. It is however not possible to fully replace the sulphuric acid of the viscose spinning bath with acetic acid of own production. The sulphuric chemicals from the viscose plant can be partly taken care of in the kraft recovery area as well as the viscose plant which can be supplied with alkali and sulphuric acid. Zinc-containing effluents from the viscose plant can be treated with green liquor to precipitate zinc sulphide.
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| 5. |
- Siwale, Workson
(författare)
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Mitigating Off-Gassing and Self-Heating in Fuel Wood Pellets Storage : A Raw Materials Selection and Pre-Treatment Centred Approach
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wood pellets have become a preferred solid biomass fuel for heat and power generation due to their standardized nature, known properties, and consistent quality. However, pellets produced from fresh sawdust sometimes undergo self-heating and off-gassing during storage. This poses a challenge for their transportation and storage. The aim of this thesis was to increase the body of knowledge towards understanding the mechanisms underlying the self-heating and off-gassing of wood pellets, and offer solutions for producing wood pellets from freshly generated sawdust, with reduced self-heating and off-gassing tendencies.The effects of total wood extractive content and types of extractives in the raw material on off-gassing of wood pellets were investigated through two separate studies (papers I and II). The results from paper I showed that the total amount of extractives in the raw material has little effect on off-gassing. While gas emissions were reduced for pellets produced from Scots pine sawdust that had low amounts of extractives (stored and acetone extracted), the coefficients of determination (R2) from the linear correlation analysis between off-gassing and the total extractive content of the raw materials were below 0.5 for all the three off-gasses indicating low or no correlation. The results of cellulose pellets with added additive oils (paper II) showed that the off-gassing is highly dependent on the type of extractives in the raw material. The highest mean concentrations of the carbon oxides and methane were recorded from cellulose pellets with added linseed oil. Pellets with added linseed oil had higher off-gas emissions due to the high content of unsaturated fatty acids of 73.9% linolenic and 7.6% linoleic.The effects of raw material type and pre-treatments on self-heating and off-gassing of wood pellets were also investigated through two separate studies (papers III and IV). The results from both studies indicated significant influences of both raw material type and drying temperature. There was a strong linear correlation between off-gassing and sapwood content, with correlation coefficient (R) values greater than 0.9 at p < 0.001 for all the off-gases (paper III). An increase in sapwood content of the raw material (fresh Scots pine sawdust) led to a significant increase in off-gassing of CO2, CO and CH4, and O2 consumption. Storing of sawdust for over six months prior to pellet production, and increasing the temperature of drying the sawdust led to significant reduction of off-gassing for sapwood pellets. For heartwood pellets, increasing the drying temperature resulted in increased off-gassing and raw material storage had no effect. In the other study (paper IV), the pellets produced from Scots pine mature wood sawdust were more prone to self-heating and off-gassing compared to those produced from juvenile wood sawdust. Steam drying the sawdust at high temperature and pressure led to a significant reduction in heat and gas generation for both materials. Furthermore, the study established a notable connection between self-heating and off-gassing, the storage piles with high temperature increase also exhibited high concentrations of off-gases.The overall results indicated that a biological process, in combination with the chemical oxidation of unsaturated fatty acids lay behind the self-heating and off-gassing of wood pellets. The other notable effect was that methane formation is dependent on anaerobic conditions, whereas formation of carbon oxides can occur both under aerobic and anaerobic conditions. While storing fresh sawdust for a period of time prior to pellet production remains the most effective method for mitigating self-heating and off-gassing during pellet storage, sorting and separating the raw materials at source can facilitate the development of storage schedules tailored to specific raw materials, thereby reducing on the raw material storage time.
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| 6. |
- Siwale, Workson
(författare)
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Understanding the Influence of Wood Extractives on Off-Gassing during Storage of Wood Pellets
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wood pellets have become a solid biomass fuel of choice because they are a standardized product with known quality properties. However, the self-heating and off-gassing tendencies during storage of wood pellets threatens the consistency of the pellets’ quality properties. The aim of this thesis was to increase the body of knowledge towards understanding of the off-gassing of wood pellets. The effects of total wood extractive content and types of extractives in the raw material on off-gassing of wood pellets were investigated through two separate studies. In the first study, the pellets were produced from fresh and pre-treated Scots pine sawdust. The pre-treatments involved storing, extraction and adding additive oils. The second study used synthetic pure cellulose that was pre-treated by adding different additive oils. The pellets were subjected to off-gassing tests under controlled conditions.The results from the first study showed that the total amount of extractives in the raw material has little effect on off-gassing. While gas emissions were reduced for stored and acetone extracted pine pellets, the coefficients of determination (R2) from the linear correlation analysis between off-gassing and the total extractive content of the raw materials were below 0.5 for all the three off-gasses indicating no correlation. The results of cellulose pellets with added additive oils in the second study showed that the off-gassing is highly dependent on the type of extractives in the raw material. The highest mean concentrations of the carbon oxides and methane were recorded from cellulose pellets with added linseed oil. Pellets with added linseed oil had higher off-gas emissions due to the high content of unsaturated fatty acids of 73.9% linolenic and 7.6% linoleic. Based on these results, it was concluded that one of the main causes of off-gassing during storage of wood pellets is the α-oxidation of unsaturated fatty acids. The other notable effect was that methane formation is dependent on anaerobic conditions, whereas formation of carbon oxides can occur both under aerobic and anaerobic conditions.
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| 7. |
- Areskogh, Dimitri, 1982-
(författare)
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Structural Modifications of Lignosulphonates
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lignosulphonates are by‐products from the sulphite pulping process for the manufacture ofspecialty dissolving pulps and paper. During the liberation of the cellulose, the lignin isfractionated and solubilised through covalent addition of sulphonic acid groups at variouspositions in the structure. The formed sulphonated lignin, lignosulphonate is then furtherisolated and refined. The amphiphilic nature of lignosulphonates has enabled them to be used as additives to varioussuspensions to improve their dispersion and stability. The by far largest utilisation oflignosulphonates is as dispersants in concrete. Here, lignosulphonates act by dispersing cementparticles to prevent flocculation, un‐even particle distribution and reduced strengthdevelopment. The dispersion is achieved through steric and electrostatic repulsion of the cementparticles by the lignosulphonate polymer. This behaviour is intimately linked with the overallsize and amount of charged groups in the dispersing polymer. Traditional modifications oflignosulphonates have been limited to removal of sugars, filtration and fractionation. Thesemodifications are not sufficient for utilisation of lignosulphonates in high‐strength concrete. Heresynthetic dispersants and superplasticisers are used which are considerably more efficient evenat low dosages. To compete with these, additional modifications of lignosulphonates are likely tobe necessary. The molecular weight and functional group composition have been identified anddescribed as the most interesting parameters that can be modified. Currently, no suitable method exists to increase the molecular weight of lignosulphonates.Oxidation by the natural radical initiating enzyme laccase is an interesting tool to achieve suchmodifications. In this thesis several aspects of the mechanism through which this enzyme reactswith lignin and lignosulphonate structures have been elucidated through model compoundstudies. Further studies showed that laccase alone was a highly efficient tool for increasing themolecular weight of commercial lignosulphonates at low dosages and in short incubation times.Immobilisation of the laccase to a solid support to enable re‐utilisation was also investigated. Modification of functional group composition of lignosulphonates was achieved throughozonolysis and the Fenton’s reagent, a mixture of hydrogen peroxide and iron(II)acetate.Introduction of charged carboxylic groups was achieved through opening of the benzyl rings oflignosulphonates. It was found that a two‐stage process consisting of laccase oxidation followedby ozonolysis was an efficient technique to create a polymer enriched with carboxylic acidgroups with a sufficient molecular size. Oxidation by the Fenton’s reagent was shown to yield similar modifications as the combinedlaccase/ozonolysis treatment albeit with less pronounced results but with a large level of controlthrough variation of a number of reaction parameters. The Fenton’s reagent can therefore be aninteresting alternative to the aforementioned two‐stage treatment. These modifications are interesting for large‐scale applications not only because of theirsimplicity in terms of reaction parameters but also because of the ubiquity of the used enzymeand the chemicals in the pulp and paper industry.
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| 8. |
- Moser, Carl, 1987-
(författare)
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Manufacturing and Characterization of Cellulose Nanofibers
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The usage of wood has been a dominant driving force during the evolution of the human species. It allowed us to cook food, build tools, put roofs over our head and explore the world. The fibers making up the tree has been the most important way to store and transmit knowledge in the form of paper for centuries. It may not be considered as the most interesting or hi-tech of fields, although, nothing could be further from the truth. One of society's most significant issue is how to live sustainably, which is coincidentally exactly what trees can solve. We can live in tall buildings made from wood, locking up vast amounts of carbon dioxide - we can replace many of the plastics we use today with sustainable alternative from the components making up the tree - we could even make clothes from our trees and stop being reliant on the untenable cotton production - only our imagination is holding us back from what can be made from trees.Cellulose is the structural component in trees, the molecule arranges itself in a complex hierarchical structure that forms the wood-cells, or fibers. Breaking down this hierarchical structure down to its smallest structural units leaves us with tiny fibers, no longer than a few micrometers and with a width of merely four nanometers. These are cellulose nanofibers, and this work has aimed to understand how and what it takes to liberate these fine fibers from the larger fiber that they make up. Two main pathways exist to liberate the nanofibers, either chemically by introducing negatively charged groups on the surface of the cellulose, making the fibrils repel each other, or mechanically, simply by intense processing of the fibers. However, these processes are associated with certain flaws in that (i) vast amount of energy is required unless the fibers are pretreated, (ii) disintegration is performed in instruments that do not scale well, (iii) disintegration is carried out at a low concentration of fibers, typically below 5%. Additionally, what comes out of a process is difficult to characterize in terms of quality due to an inherent inhomogeneity and the small size of the nanofibers.These issues in combination with a greater understanding of the processes are the foundation of this thesis.Decreased energy consumption and scalability was explored via the steam explosion concept Nanopulp. In order to avoid issues associated with the low concentration, a method was developed for drying cellulose nanofibers to a paste without causing hornification using glycerol. A variety of cellulose nanofibers from different sources were prepared and characterization techniques were compared and expanded upon, including the development of a method for better describing the surface area of cellulose nanofibers. Finally, an environmentally friendly composite was made using cheap and available resources in combination with cellulose nanofibers.
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| 9. |
- Östberg, Linda, 1975-
(författare)
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Some Aspects on Pulp Pre-treatment Prior to Viscose Preparation
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Large amounts of carbon disulphide are consumed in the conventional production of viscose. Until a novel, eco-friendly, wood-based process for the production of cellulose textile fibres has been developed and implemented, it is important to try to find ways to improve the conventional viscose process, e.g. in terms of reducing the carbon disulphide requirement of the process. The aim of this thesis was to reduce the amount of carbon disulphide consumed in the preparation of high-viscosity viscose by pre-treating pulps with enzymes. It also aimed at investigating and linking the different measurements of reactivity, i.e. gamma number, Fock reactivity and Kw, and determining the sensitivity of the gamma number to the hemicellulose content of pulp. Reactivity was measured as Fock reactivity and gamma number. The gamma number of viscose solutions remained unchanged when an enzyme stage was used prior to the viscose process. The gamma number analysis was found to be selective not only to cellulose but also to the hemicellulosic material. It was verified that both cellulose and hemicellulose molecules in the pulp material were substituted in the viscose preparation stages, showing that the gamma number of the pulp is due to both substituted cellulose and substituted hemicelluloses. The mechanisms responsible for the Fock reactivity, or the filter-clogging value (Kw) on the one hand and the gamma number on the other, are probably not the same. It was speculated that the analysis method employed in Fock´s test and the filter-clogging value measure the results on a fibre level, whereas the gamma number measures changes mainly on a molecular level. This could explain the difference in the levels of reactivity found in this study.
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| 10. |
- Andersson, Alexander, et al.
(författare)
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Presence of Calcium Cations Stimulate Alkaline Hydrolysis of Cellulose During Kraft Pulping Conditions
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Simulated kraft pulping has been performed on cotton linters fibers consisting of almost pure cellulose with varying content of calcium ions. These concentrations were obtained by soaking and drying cotton linters in calcium sulfate solutions. The viscosities of the pulped fibers were generally lower with higher calcium ion concentration and, therefore, in line with earlier suggested ideas that calcium ions could catalyze alkaline hydrolysis. The technical importance of these results is discussed.
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| 11. |
- Berglund, Jennie, et al.
(författare)
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Acetylation and Sugar Composition Influence the (In)Solubility of Plant beta-Mannans and Their Interaction with Cellulose Surfaces
- 2020
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Ingår i: ACS Sustainable Chemistry and Engineering. - : AMER CHEMICAL SOC. - 2168-0485. ; 8:27, s. 10027-10040
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Tidskriftsartikel (refereegranskat)abstract
- Plant beta-mannans are complex heteropolysaccharides that represent an abundant resource from lignocellulosic biomass. The influence of the molecular motifs of plant mannans on the backbone flexibility, solubility, and the interaction with cellulose was investigated by computational and experimental approaches. The regioselectivity of the acetyl substitutions at C2 and C3 distinctively influenced backbone flexibility in aqueous media, as revealed by molecular dynamic simulations. The molecular weight and degree of acetylation were tailored for two model seed mannans (galactomannan and glucomannan) and compared to spruce acetylated galactoglucomannan. The thermal stability was enhanced with increasing acetyl substitutions, independently of the type of mannan. Dynamic light scattering and atomic force microscopy revealed that the occurrence of galactosylation and a low degree of acetylation (similar to that of native acetylated galactoglucomannans) enhanced solubility/dispersibility of mannans, whereas the solubility/dispersibility decreased for higher degrees of acetylation. Mannan solubility influenced their interactions with cellulose at water-cellulose interfaces in terms of adsorbed mass and viscoelastic properties of the adsorbed mannan layers. Our results reveal that modulating the molecular motifs of plant beta-mannans influences their macromolecular conformation and physicochemical properties, with fundamental implications for their role in the plant cell wall and the design of wood-based materials.
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| 12. |
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| 13. |
- Berglund, Jennie, et al.
(författare)
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Wood hemicelluloses exert distinct biomechanical contributions to cellulose fibrillar networks
- 2020
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Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Hemicelluloses, a family of heterogeneous polysaccharides with complex molecular structures, constitute a fundamental component of lignocellulosic biomass. However, the contribution of each hemicellulose type to the mechanical properties of secondary plant cell walls remains elusive. Here we homogeneously incorporate different combinations of extracted and purified hemicelluloses (xylans and glucomannans) from softwood and hardwood species into self-assembled networks during cellulose biosynthesis in a bacterial model, without altering the morphology and the crystallinity of the cellulose bundles. These composite hydrogels can be therefore envisioned as models of secondary plant cell walls prior to lignification. The incorporated hemicelluloses exhibit both a rigid phase having close interactions with cellulose, together with a flexible phase contributing to the multiscale architecture of the bacterial cellulose hydrogels. The wood hemicelluloses exhibit distinct biomechanical contributions, with glucomannans increasing the elastic modulus in compression, and xylans contributing to a dramatic increase of the elongation at break under tension. These diverging effects cannot be explained solely from the nature of their direct interactions with cellulose, but can be related to the distinct molecular structure of wood xylans and mannans, the multiphase architecture of the hydrogels and the aggregative effects amongst hemicellulose-coated fibrils. Our study contributes to understanding the specific roles of wood xylans and glucomannans in the biomechanical integrity of secondary cell walls in tension and compression and has significance for the development of lignocellulosic materials with controlled assembly and tailored mechanical properties.
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| 14. |
- Berglund, Jennie
(författare)
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Wood Hemicelluloses - Fundamental Insights on Biological and Technical Properties
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Hemicelluloses are a group of heterogeneous polysaccharides representing around 30 % of wood where the dominating types are xylans, glucomannans and xyloglucans. Hemicelluloses complex molecular structure makes it difficult to understand the relationship between structure and properties entirely, and their biological role is not yet fully verified. Additionally, hemicelluloses are sensitive to chemical processing and are not utilized to their full potentials for production of value-added products such as materials, additives to food and pharmaceutical products, etc. Increased knowledge regarding their functions is important for the development of both processes and products. The aim with this work has therefore been to increase the fundamental understanding about how the structure and properties of wood hemicelluloses are correlated, and properties such as flexibility, interaction with cellulose, solubility, resistance to chemical-, thermal-, and enzymatic degradation have been explored.Molecular dynamics (MD) simulations were used to, in detail, study the structures found in wood hemicelluloses. The flexibility was evaluated by comparing the impact of backbone sugars on the conformational space and also the impact of side groups was considered. Based on the conformational space of backbone glycosidic linkages the flexibility order of hemicelluloses in an aqueous environment was determined to be: xylan > glucomannan > xyloglucan. Additionally, the impact of xylan structure on cellulose interaction was evaluated by MD methods.Hemicelluloses were extracted from birch and spruce, and were used to fabricate different composite hydrogels with bacterial cellulose. These materials were studied with regards to mechanical properties, and it was shown that galactoglucomannans mainly contributed to an increased modulus in compression, whereas the most significant effect from xylan was increased strain under uniaxial tensile testing. Besides, other polysaccharides of similar structure as galactoglucomannans were modified and used as pure, well defined, models. Acetyl groups are naturally occurring decorations of wood hemicelluloses and can also be chemically introduced. Here, mannans with different degrees of acetylation were prepared and the influence of structure on solubility in water and the organic solvent DMSO were evaluated. Furthermore, the structure and water solubility influenced the interaction with cellulose. Acetylation also showed to increase the thermal and biological stability of mannans.With chemical pulping processes in mind, the degradability of spruce galactoglucomannans in alkaline solution were studied with regards to the structure, and the content of more or less stable structural regions were proposed.
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| 15. |
- Bi, Ran, 1985-
(författare)
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Lignocellulose Degradation by Soil Micro-organisms
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lignocellulosic biomass is a sustainable resource with abundant reserves. Compared to petroleum ‐ based products, the biomass ‐ derived polymers and chemicals give better environmental profiles. A lot of research interest is focused on understanding the lignocellulose structures.Lignin, among the three major wood components, represents most difficulty for microbial degradation because of its complex structure and because cross ‐ linking to hemicellulose makes wood such a compact structure. Nevertheless, wood is naturally degraded by wood ‐ degrading micro ‐ organisms and modified and partly degraded residual of lignin goes into soil. Therefore soil serves as a good environment in which to search for special lignin ‐ degraders. In this thesis, different types of lignin have been used as sole carbon sources to screen for lignin ‐ degrading soil micro ‐ organisms. Eleven aerobic and three anaerobic microbe strains have been isolated and identified as able to grow on lignin. The lignin degradation patterns of selected strains have been studied and these partly include an endwise cleavage of β‐ O ‐ 4 bonds in lignin and is more complex than simple hydrolytic degradation.As lignin exists in wood covalently bonded to hemicellulose, one isolated microbe strain, Phoma herbarum, has also been studied with regards to its ability to degrade covalent lignin polysaccharide networks (LCC). The results show that its culture filtrate can attack lignin ‐ polysaccharide networks in a manner different from that of the commercial enzyme product, Gammanase, possibly by selective cleavage of phenyl glucoside bonds. The effects on LCC of Phoma herbarum also enhance polymer extractability. Hot ‐ water extraction of a culture filtrate of Phoma herbarum ‐ treated fiberized spruce wood material gave an amount of extracted galactoglucomannan more than that given by the Gammanase ‐ treated material and non ‐ enzyme ‐ treated material.Over millions of years of natural evolution, micro ‐ organisms on the one hand develop so that they can degrade all wood components to get energy for growth, while plants on the other hand also continuously develop to defend from microbial attack. Compared with lignin and cellulose, hemicelluloses as major components of plant cell walls, are much more easily degraded, but hemicelluloses differ from cellulose in that they are acetylated to different extents. The biological functions of acetylation are not completely understood, but it is suggested is that one function is to decrease the microbial degradability of cell walls. By cultivation of soil micro ‐ organisms using mannans acetylated to deffernent degrees as sole carbon source on agar plates, we were able to see significant trends where the resistance towards microbial degradation of glucomannan and galactomannan increased with increasing degree of acetylation. Possible mechanisms and the technological significance of this are discussed. Tailoring the degree of acetylation of polysaccharide materials might slow down the biodegradation, making it possible to design a material with a degradation rate suited to its application.
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| 16. |
- Christiernin, Maria, 1963-
(författare)
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Composition of lignin in outer cell-wall layers
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The composition of lignin in the outer cell-wall layers of spruce and poplar has been studied and the data obtained have been compared with those of the mature reference wood in which the secondary cell wall predominates. Materials with exclusively or predominantly outer cell-wall layers were examined. Accurate data relating to the lignin monomer composition and the number of β-O-4´ bonds were obtained from pure middle lamella/primary cell wall lignin. Firstly, a 10 000 year old white spruce material, with most of the secondary cell wall missing, was studied. The aged lignin was composed of guaiacyl units only, and was slightly more condensed but otherwise similar to the reference lignin.Secondly, the developing xylem of a Norway spruce clone was analyzed during a growth season. In spring and early summer, growth is very rapid and the intention was to sample tissues in which the secondary cell-wall layers had not yet lignified, but where the outer layers at least had started to lignify. Microscopy, Klason lignin and carbohydrate analyses showed that the lignin in the developing xylem of samples from mid-June was located exclusively in the middle lamella. The lignin was more condensed, was composed of guaiacyl units only and contained more end-groups than the reference Norway spruce wood.Thirdly, the cambial tissues of a Balsam poplar clone were surveyed during a growth season. Both the phloem side and the xylem side of the cambial region were examined. The Klason lignin content and carbohydrate monomer distribution showed that in June and August the tissues on the phloem side contained material with mainly middle lamella/primary walls. In June, the xylem side in the cambial region contained mainly middle lamella/primary walls, and in August the secondary cell wall carbohydrates were being deposited. Both tissues contained lignin that was more condensed and had more end-groups than the reference lignin. In mid-June, the developing xylem had a ratio of syringyl to guaiacyl units of 0.6, whereas the ratio for the reference wood was 1.3.In the final study, lignin from the primary cell walls from a hybrid aspen cell suspension culture was investigated. The lignin contained only guaiacyl units which were more condensed than those observed in the reference poplar wood.
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| 17. |
- Dogaris, Ioannis, et al.
(författare)
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Critical parameters for tall oil separation I : The importance of the ratio of fatty acids to rosin acids
- 2019
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Ingår i: TAPPI Journal. - : TECH ASSOC PULP PAPER IND INC. - 0734-1415. ; 18:9, s. 547-555
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Tidskriftsartikel (refereegranskat)abstract
- Tall oil is a valuable byproduct in chemical pulping of wood, and its fractions have a large spectrum of applications as chemical precursors, detergents, and fuel. High recovery of tall oil is important for the economic and environmental profile of chemical pulp mills. The purpose of this study was to investigate critical parameters of tall oil separation from black liquor. To investigate this in a controlled way, we developed a model test system using a "synthetic" black liquor (active cooking chemicals OH- and HS- ions), a complete process for soap skimming, and determination of recovered tall oil based on solvent extraction and colorimetric analysis, with good reproducibility. We used the developed system to study the effect of the ratio of fatty acids to rosin acids on tall oil separation. When high amounts of rosin acids were present, tall oil recovery was low, while high content of fatty acids above 60% significantly promoted tall oil separation. Therefore, manipulating the content of fatty acids in black liquor before the soap skimming step can significantly affect the tall oil solubility, and hence its separation. The findings open up chemical ways to improve the tall oil yield. Application: Controlling the ratio of fatty acids to rosin acids in kraft pulping can significantly affect the tall oil separation and improve its yield and quality.
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| 18. |
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| 19. |
- Heinonen, Emilia, et al.
(författare)
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Xylan adsorption on cellulose : Preferred alignment and local surface immobilizing effect
- 2022
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 285, s. 119221-119221
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Tidskriftsartikel (refereegranskat)abstract
- Interaction between xylan and cellulose microfibrils is required to maintain the integrity of secondary cell walls. However, the mechanisms governing their assembly and the effects on cellulose surface polymers are not fully clear. Here, molecular dynamics simulations are used to study xylan adsorption onto hydrated cellulose fibrils. Based on multiple spontaneous adsorption simulations it is shown that an antiparallel orientation is thermodynamically preferred over a parallel one, and that adsorption is accompanied by the formation of regular but orientation-dependent hydrogen bond patterns. Furthermore, xylan adsorption restricts the local dynamics of the adjacent glucose residues in the surface layer to a level of the crystalline core, which is manifested as a three-fold increase in their 13C NMR T1 relaxation time. These results suggest that xylan forms a rigid and ordered layer around the cellulose fibril that functions as a transition phase to more flexible and disordered polysaccharide and lignin domains.
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| 20. |
- Henriksson, Gunnar, et al.
(författare)
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Ways to tailor-make xylan for kraft pulping
- 2011
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Ingår i: Proceedings 16th International Symposium on Wood, Fiber and Pulping Chemistry, ISWFPC. - : China Light Industry Press. ; , s. 596-599
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Konferensbidrag (refereegranskat)abstract
- Genetic manipulation of trees in order to produce raw material with different chemical composition, which will perform better in pulping and bleaching, has gained large interest the last decade. Most efforts have been on increasing cellulose content, and modifying the lignin structure so that the pulping will be more efficient. Less interest has been focused on the hemicellulose structures, although many important chemical reactions occur on hemicelluloses during kraft pulping. For instance, hexenuronic acid is formed from 4-O-methyl glucuronic acid, a side group on xylan. This structure is a main contributor to the kappa number in the unbleached pulp, especially in hardwoods, and requires relatively strong bleaching agents for efficient removal. Remaining hexenuronic acid in the bleached pulp may furthermore cause post yellowing. In model experiments, we have simulated kraft cooking, and shown that hexenuronic acid is formed to a much lower degree from unmethylated glucuronic acid, than from 4-O-methylglucuronic acid. A tree without methyl groups on its glucuronic acid residues on xylan, is therefore expected to be pulped to a much lower kappa number, and to be easy to bleach to high brightness stability. According to a literature study, the possibilities to make such a tree by genetically manipulation appear to be promising. There might also be other ways, in which hemicelluloses structure can be manipulated.
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| 21. |
- Lindén, Pär A., et al.
(författare)
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Adapting the kraft cooking process in glycerol media. Studies of impregnation kinetics
- 2023
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Ingår i: Nordic Pulp & Paper Research Journal. - : De Gruyter Open Ltd. - 0283-2631 .- 2000-0669. ; 38:1, s. 9-18
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Tidskriftsartikel (refereegranskat)abstract
- Although organosolv processes using high-boiling solvents have been investigated in recent decades for developing novel industrial processes, there are potential benefits of using high-boiling point solvents for traditional sulphate-based cooking processes, both from an industrial perspective and from a laboratory perspective. Using high-boiling solvents, experiments can be done under atmospheric conditions, thus making it easier to continually monitor laboratory experiments and extracting aliquots at desired intervals. Using such a system, alkaline consumption was monitored during impregnation of spruce chips in glycerol media using chemical charges of 1 M NaOH and 0.1 M NaHS, i. e., kraft pulping conditions, and compared to a similar investigation of alkaline consumption in water media using steel autoclaves. The resulting data was fitted to a first order kinetic model, with an apparent activation energy of 22 kJ mol-1 in glycerol media. Finally, a "normal quality pulp"of kappa number 28 and a viscosity of 1113 ml g-1 was successful produced using a cooking process with an impregnation step at 140 °C for 3 h and a cooking step at 160 °C for 4 h. A nuclear magnetic resonance study on the dissolved lignin produced for said experiment showed characteristics typical of other kraft lignins.
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| 22. |
- 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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| 23. |
- Mattsson, Tuve, et al.
(författare)
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Towards a wood based material biorefinery - A demonstrator
- 2015
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Ingår i: 6th Nordic Wood Biorefinery Conference, NWBC 2015. - : VTT Technical Research Centre of Finland. - 9789513883539 ; , s. 92-101
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Konferensbidrag (refereegranskat)abstract
- Wood, the most abundant ligno-cellulosic raw material available, is a key potential feedstock for production of more sustainable alternatives to fossil-based materials. However advances within the fields of extraction and treatment processes within what is often referred to as the biorefinery concept is essential to allow for such transition. In this study, several different methods for the extraction and separation of wood constituents have been combined in a single process with the purpose of achieving a high overall efficiency of material extraction and utilisation. The work builds on several activities within the Wallenberg Wood Science Center (WWSC). The aim is to present a laboratory-scale demonstrator that illustrates how the different constituents can be separated from the wood matrix for later use in the production of bio-based materials and chemicals. The process steps involved have been tested as integral steps in a linked process for a scale of operations that range from the kilogram-scale down to the gram-scale. Industrially chipped softwood, containing mainly spruce with some pine, was used as raw material.
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| 24. |
- Moser, Carl, 1987-, et al.
(författare)
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Xyloglucan adsorption for measuring the specific surface area on various never-dried cellulose nanofibers
- 2018
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Ingår i: Nordic Pulp & Paper Research Journal. - Berlin : De Gruyter Open. - 0283-2631 .- 2000-0669. ; 33:2, s. 186-193
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we explore xyloglucan adsorption to cellulose nanofibers as a method for the evaluation of their quality (i. e., the degree of disintegration) and the accessible surface area in the wet state and at low ionic strength. This method was shown to be capable of estimating the surface areas of 14 different cellulose nanofiber qualities from both hardwood and softwood with different pretreatments, including enzymatic hydrolysis using a monocomponent endoglucanase, TEMPO-mediated oxidation, and carboxymethylation. The cellulose surface measured using this method showed a correlation with the degree of disintegration expressed as transmittance for different concentrations of xyloglucan.
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| 25. |
- Nasr, Patrik, et al.
(författare)
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A rapid, non-invasive, clinical surveillance for CachExia, sarcopenia, portal hypertension, and hepatocellular carcinoma in end-stage liver disease : the ACCESS-ESLD study protocol
- 2023
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Ingår i: BMC Gastroenterology. - : BioMed Central (BMC). - 1471-230X. ; 23:1
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Liver cirrhosis, the advanced stage of many chronic liver diseases, is associated with escalated risks of liver-related complications like decompensation and hepatocellular carcinoma (HCC). Morbidity and mortality in cirrhosis patients are linked to portal hypertension, sarcopenia, and hepatocellular carcinoma. Although conventional cirrhosis management centered on treating complications, contemporary approaches prioritize preemptive measures. This study aims to formulate novel blood- and imaging-centric methodologies for monitoring liver cirrhosis patients.METHODS: In this prospective study, 150 liver cirrhosis patients will be enrolled from three Swedish liver clinics. Their conditions will be assessed through extensive blood-based markers and magnetic resonance imaging (MRI). The MRI protocol encompasses body composition profile with Muscle Assement Score, portal flow assessment, magnet resonance elastography, and a abbreviated MRI for HCC screening. Evaluation of lifestyle, muscular strength, physical performance, body composition, and quality of life will be conducted. Additionally, DNA, serum, and plasma biobanking will facilitate future investigations.DISCUSSION: The anticipated outcomes involve the identification and validation of non-invasive blood- and imaging-oriented biomarkers, enhancing the care paradigm for liver cirrhosis patients. Notably, the temporal evolution of these biomarkers will be crucial for understanding dynamic changes.TRIAL REGISTRATION: Clinicaltrials.gov, registration identifier NCT05502198. Registered on 16 August 2022. Link: https://classic. CLINICALTRIALS: gov/ct2/show/NCT05502198 .
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| 26. |
- Nyström, Peter, 1959-
(författare)
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Rätt mätt på prov : Om validering av bedömningar i skolan
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The thesis focuses on validation as a process whereby the quality of educational assessments can be evaluated. On the basis of Messick’s (1989) validity concept, which takes consequences as well as inferences of assessment results into account, a model for validation is described. An argument made is that assessment purposes, epistemology, and curricular goals are necessary starting points for validation. Fur-thermore, it is argued that several of the criteria for good assessment proposed as alternatives to validity and reliability can be used together with Messick’s frame-work for validity and make it useful in practice. Four empirical studies, each pre-sented in a separate paper, supply examples of the application of this framework. In paper I it is claimed that reliability is a problem inherent in all educational assess-ments, and it is given a meaningful interpretation through the concept of classifica-tion accuracy. The article examines how the classification accuracy of a Swedish national test in mathematics is affected by changes in the test that are motivated by other validity concerns. The study is based on the results of 1,201 students partici-pating in a Swedish national test in mathematics. The results indicate that there can be a significant trade-off between reliability and other aspects of validity. Paper II presents a study of attainment differences in mathematics related to the grouping of students into different study programmes in the Swedish upper-secondary school. For a sample of 403 students, results from two consecutive national tests in mathe-matics were compared, one at the end of compulsory school and the other at the end of the first mathematics course in upper-secondary school. The results indicate that attainment is, on average, positively affected if students are grouped together with higher-achieving peers. This effect appears to be strongest for low-achievers. Paper III addresses questions concerning how perceptions of competence are formed in school mathematics. The study is based on a questionnaire distributed to a sample of Swedish upper secondary school students (n = 550). The results indicate that an inner feeling of understanding is most highly valued by the students as an indicator of competence, more than external cues like test results and teacher feed-back. Male and female students seem to value cues to perceived competence in similar ways. In paper IV an interview study with six mathematics teachers in upper-secondary school is presented, aiming at exploring the variation in what teachers at their particular school say about ability grouping. In summary, what these teachers express concerning the advantages and disadvantages of ability grouping varies a great deal. There are, however, some things they more or less agree on. They have a basically positive view of the way in which ability grouping has been practised at their school. They identify problems with ability grouping for low-ability groups, primarily related to the mixing of students who have trouble learning with those who primarily have motivational problems. The list of advantages and possibilities is definitely longer for groups of high-achieving students compared to groups of low-achievers.
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| 27. |
- Oinonen, Petri, 1978-
(författare)
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A biomimicking approach for hemicellulose processing
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lignocellulose can become the best opportunity for the society to reduce its dependency on the harmful petroleum based products as well as to produce clean energy. In each part of the production cycle, biomass based products have a better environmental profiles than their petroleum based counterparts. Woody biomass has a vast availability, but it suffers from recalcitrance that is mostly caused by lignin that is functioning as a matrix, surrounding and binding the carbohydrates that are currently the most valuable of the wood components.Lignin-carbohydrate (LC) bonds are believed to be a key element in this recalcitrance and research has shown that these types of bonds are common in wood. These bonds are important in an economical point of view as well, as e.g. residual lignin structures in pulp (lignins bonded to the cellulose and hemicelluloses) require expensive bleaching sequences for their removal.The LC-structures can also be exploited technically as we now have demonstrated. We developed a method that utilizes phenolic end groups that are bonded to different hemicelluloses for cross-linking. The enzyme laccase was used for the cross-linking to create a cost-efficient processing scheme to both isolate and increase the molecular weight of the hemicelluloses. Membrane filtration was used as the key separation technique, which enables the establishment of industrial scale production. The final product had improved mechanical and thermal properties and could be used e.g. as barrier film component in renewable packaging. Nanocomposite formation with nanofibrillated cellulose was also studied. This improved the film properties further. The complexes are also possible to use as model compounds for lignin-carbohydrate complexes in wood.This technique can also be seen to mimick the lignification and lignin-carbohydrate network formation phenomena in plants enabling the formation of entire networks of wood components. Our results suggests that the side chains of hemicellulose might play an important role in network formation and that hemicellulose molecules can carry more than one lignin phenolic end group to fulfill this capability.
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| 28. |
- Vegunta, Vijaya Lakshmi, et al.
(författare)
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Addition of Green and Black Liquor in Kraft Pulping of Eucalyptus dunnii wood : Possible Solutions for the Problems with Kraft Pulping Caused by High Calcium Content.
- 2023
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Samples of Eucalyptus dunnii with high calcium content have less good pulping properties regarding delignification and polysaccharide degradation, as it was shown by us earlier. In this work, we tested the addition of black liquor and green liquor to the Eucalyptus dunnii chips before kraft pulping, Specific improvements were obtained with both liquors, but the most substantial effect was observed with the green liquor, where even wood with the highest calcium content was pulped with a good result. Delignification was faster, and viscosity losses (degree of polymerization of cellulose) were higher for samples treated with green liquor prior to kraft pulping. Bleaching experiments showed that the bleachability of the green liquor-treated pulp was virtually the same as for a control pulp and that the higher viscosity of the bleached pulp was maintained. Possible chemical explanations for the results obtained are discussed.
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