| 1. |
- Henriksson, Gunnar, et al.
(author)
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Endoglucanase 28 (Cel12A), a new Phanerochaete chrysosporium cellulase.
- 1999
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In: European Journal of Biochemistry. - 0014-2956 .- 1432-1033. ; 259:1-2, s. 88-95
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Journal article (peer-reviewed)abstract
- A 28-kDa endoglucanase was isolated from the culture filtrate of Phanerochaete chrysosporium strain K3 and named EG 28. It degrades carboxymethylated cellulose and amorphous cellulose, and to a lesser degree xylan and mannan but not microcrystalline cellulose (Avicel). EG 28 is unusual among cellulases from aerobic fungi, in that it appears to lack a cellulose-binding domain and does not bind to crystalline cellulose. The enzyme is efficient at releasing short fibres from filter paper and mechanical pulp, and acts synergistically with cellobiohydrolases. Its mode of degrading filter paper appears to be different to that of endoglucanase I from Trichoderma reesei. Furthermore, EG 28 releases colour from stained cellulose beads faster than any other enzyme tested. Peptide mapping suggests that it is not a fragment of another known endoglucanases from P. chrysosporium and peptide sequences indicate that it belongs to family 12 of the glycosyl hydrolases. EG 28 is glycosylated. The biological function of the enzyme is discussed, and it is hypothesized that it is homologous to EG III in Trichoderma reesei and the role of the enzyme is to make the cellulose in wood more accessible to other cellulases.
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| 2. |
- Henriksson, Chris, 1938-, et al.
(author)
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Evaluation of four outpatient educational programmes for patients with longstanding fibromyalgia
- 2004
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In: Journal of Rehabilitation Medicine. - : Medical Journals Sweden AB. - 1650-1977 .- 1651-2081. ; 36:5, s. 211-219
-
Journal article (peer-reviewed)abstract
- OBJECTIVE: Four programmes based on educational and cognitive principles but with a variation in total length and number of staff/patient contact hours were compared in order to gain further insight into the importance of the format of the programme for the final outcome.DESIGN: A prospective non-randomized intervention study with 191 persons with fibromyalgia. Data were collected before, after and at 1-year follow-up. Participants served as their own controls. Results within and between the programmes were calculated.METHODS: Clinical investigations before and after intervention. Questionnaires were answered before, after and at 1-year follow-up.RESULTS: Most instruments showed no significant improvements after the programme. However, some improvements were found in important variables such as attitudes, self-efficacy, vitality and "days feeling well". Results were unchanged at the 1-year follow-up and 16 persons had started working. Seven had ceased working. Participants reported frequent use of coping strategies in everyday life. No major differences could be found between the programmes. Conclusions: More comprehensive programmes did not produce better results at group level. Also short and less costly interventions based on educational and cognitive principles were valuable for persons with longstanding fibromyalgia. More attention must be given to evaluating the clinical effect of programmes.
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| 3. |
- Henriksson, Gunnar, et al.
(author)
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A critical review of cellobiose dehydrogenases
- 2000
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In: Journal of Biotechnology. - : ELSEVIER SCIENCE BV. - 0168-1656 .- 1873-4863. ; 78:2, s. 93-113
-
Research review (peer-reviewed)abstract
- Cellobiose dehydrogenase (CDH) is an extracellular enzyme produced by various wood-degrading fungi. It oxidizes soluble cellodextrins, mannodextrins and lactose efficiently to their corresponding lactones by a ping-pong mechanism using a wide spectrum of electron accepters including quinones, phenoxyradicals, Fe3+, Cu2+ and tiiodide ion. Monosaccharides, maltose and molecular oxygen are:poop substrates. CDH that adsorbs strongly and specifically to cellulose carries two prosthetic groups; namely, an FAD and a heme in two different domains that can be separated after limited proteolysis. The FAD-containing fragment carries all known catalytic and cellulose binding properties. One-electron accepters, like ferricyanide, cytochrome c and phenoxy radicals, are, however, reduced more slowly by the FAD-fragment than by the intact enzyme, suggesting that the function of the heme group is to facilitate one-electron transfer. Non-heme forms of CDH have been found in the culture filtrate of some fungi (probably due to the action of fungal proteases) and were for a long time believed to represent a separate enzyme (cellobiose:quinone oxidoreductase, CBQ). The amino acid sequence of CDH has been determined and no significant homology with other proteins was detected for the heme domain. The FAD-domain sequence belongs to the GMC oxidoreductase family that includes, among others, Aspergillus niger glucose oxidase. The homology is most distinct in regions that correspond to the FAD-binding domain in glucose oxidase. A cellulose-binding domain of the fungal type is present in CDH from Myceliophtore thermophila (Sporotrichum thermophile), but in others an internal sequence rich in aromatic amino acid residues has been suggested to be responsible for the cellulose binding. The biological function of CDH is not fully understood, but recent results support a hydroxyl radical-generating mechanism whereby the radical can degrade and modify cellulose, hemicellulose and lignin. CDH has found technical use in highly selective amperometric biosensors and several other applications have been suggested.
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| 4. |
- Henriksson, Gunnar, 1965-, et al.
(author)
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Monocomponent endoglucanases : an excellent tool in wood chemistry and pulp processing
- 2005
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In: 13th ISWFPC (International Symposium on Wood, Fibre and Pulping Chemistry), Auckland, New Zealand, 16-19 May 2005: Proceedings. ; , s. 503-508
-
Conference paper (peer-reviewed)abstract
- Highly pure cellulases of endoglucanase type produced by genetically modified fungi are commercially available. They are useful tools both for analytical wood chemistry and potentially also as industrial chemicals for novel processes for the pulp and paper industry. Here the functionality of cellulases and some application of endoglucanases are reviewed. The mechanisms behind the effects of the enzyme are discussed.
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| 5. |
- Henriksson, Gunnar, et al.
(author)
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Substrate specificity of cellobiose dehydrogenase from Phanerochaete chrysosporium
- 1998
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In: Biochimica et Biophysica Acta. - 0006-3002 .- 1878-2434. ; 1383:1, s. 48-54
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Journal article (peer-reviewed)abstract
- Substrate structural mapping suggests that the catalytic site of cellobiose dehydrogenase from Phanerochaete chrysosporium forms a narrow cave with two hexose binding subsites, Kinetic data also show that beta-di or oligosaccharides are favored electron donors with respect to both KM and kcat. Surprisingly, thiocellobiose showed an even higher kcat than cellobiose, although the KM value was somewhat higher. The CDH was purified using an updated protocol.
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| 6. |
- Henriksson, Marielle, et al.
(author)
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An environmentally friendly method for enzyme-assisted preparation of microfibrillated cellulose (MFC) nanofibers
- 2007
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In: European Polymer Journal. - : Elsevier BV. - 0014-3057 .- 1873-1945. ; 43:8, s. 3434-3441
-
Journal article (peer-reviewed)abstract
- Microfibrillated cellulose nanofibers (MFC) provide strong reinforcement in polymer nanocomposites. In the present study, cellulosic wood fiber pulps are treated by endoglucanases or acid hydrolysis in combination with mechanical shearing in order to disintegrate MFC from the wood fiber cell wall. After successful disintegration, the MFC nanofibers were studied by atomic force microscopy (AFM). Enzyme-treatment was found to facilitate disintegration, and the MFC nanofibers produced also showed higher average molar mass and larger aspect ratio than nanofibers resulting from acidic pretreatment.
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| 7. |
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| 8. |
- Kjellander, Marcus
(author)
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Nanoporous Aluminum Oxide – A Promising Support for Modular Enzyme Reactors
- 2013
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Doctoral thesis (other academic/artistic)abstract
- Nanoporous alumina is a rather newly characterized material that so far has found limited use in the construction of bioreactors. The material has many advantages compared to conventional immobilization matrices. I have investigated its use in flow-through bioreactors. The rigidity and porous structure of the material makes it an excellent choice for multienzyme reactor construction. The total activity in a reactor is easily controlled by the number of membranes since the porosity makes the material less prone to increase flow system pressure. This bioreactor is suitable for characterization of new enzymes since the amount of immobilized enzyme is standardized and the enzyme may be reused many times.We designed a simple stepwise technique for covalent immobilization on this matrix in a monolayer to minimize mass transfer effects in the reactor function. The kinetic parameters for ten different substrates were investigated for immobilized alcohol oxidase and, as a second step, a two-step reactor was also designed by addition of horseradish peroxidase. This bienzymatic reactor was, in turn, employed for measuring injected alcohol concentrations. The use of the matrix for substrate specificity screening was proven for two new epsilon-class glutathione transferases from Drosophila melanogaster. Immobilized trypsin showed a substantially prolonged lifetime and its potential use as an on-line digestion unit for peptide mass fingerprinting was also demonstrated. Finally, I investigated the immobilization of the model enzyme lactate dehydrogenase by adsorption mediated by metal ion chelation similar to IMAC. Regeneration was here possible multiple times without loss of capacity. In conclusion, immobilization of enzymes on nanoporous alumina is a convenient way to characterize, stabilize and reuse enzymes.
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| 9. |
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| 10. |
- Lawoko, M., et al.
(author)
-
Hemicellulase activity of aerobic fungal cellulases
- 2000
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In: Holzforschung. - 0018-3830 .- 1437-434X. ; 54:5, s. 497-500
-
Journal article (peer-reviewed)abstract
- Cellulases isolated from Trichoderma reesei and Phanerochaete chrysosporium were screened for hemi-cellulolytic, pectinolytic and cellulolytic activity using locust bean mannan, birchwood xylan, citrus fruit pectin and carboxymethylated cellulose (CMC) as substrates. The purpose of this work was to choose appropriate enzymes to include in a miniature cellulase system with minimal hemicellulase activity for the preparation of lignin-carbohydrate complexes (LCCs). The endoglucanases showed CMC activity whereas activity towards the substrate was not detected for the CBHs. Xylanase activity was observed for EG I and EG 38 whereas mannanase activity was observed for EG 44. None of the enzymes degraded pectin. The results suggest that CBH I, CBH II, CBH 58, EG II and EG III are good candidates for the effective preparation of LCCs. The possible biological function for the hemicellulolytic activity of cellulases is discussed.
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| 11. |
- Nutt, Anu, et al.
(author)
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Conversion of O2 species by cellobiosedehydrogenase (cellobiose oxidase) and glucose oxidase — a comparison
- 1997
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In: Biotechnology letters. - 0141-5492 .- 1573-6776. ; 19:4, s. 379-384
-
Journal article (peer-reviewed)abstract
- Cellobiose dehydrogenase from Phanerochaete chrysosporium produces H2O2 by electron transfer between cellobiose and O-2 with a lower yield than the 1:1:1 molar ratio displayed by Aspergillus niger. glucose oxidase in the similar reaction between glucose and O-2. The discrepancy could best be explained if both a Fenton's reaction and the spontaneous reactivity of the oxygen species formed were taken into account.
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| 12. |
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| 13. |
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| 14. |
- Siwale, Workson
(author)
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Understanding the Influence of Wood Extractives on Off-Gassing during Storage of Wood Pellets
- 2022
-
Licentiate thesis (other academic/artistic)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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| 15. |
- Zhang, Jing, 1971-
(author)
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Biochemical Study and Technical Applications of Fungal Pectinase
- 2006
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Doctoral thesis (other academic/artistic)abstract
- Pectinases are a group of enzymes produced by bacteria, fungi, higher plants and animals. Pectinases can modify and degrade pectins, a class of heterogeneous and multifunctional polysaccharides present in middle lamellae and primary cell walls of plants. Pectins have been showed to play diverse roles in cell physiology, growth, adhesion and separation. Pectinases are used technically in the processing of fiber production and fruit juice or wine making. We have studied the mechanisms and applications of pectinases, especially in retting, a microbiological process where bast fibers in flax and other bast fiber cultivars are released from each other and from the woody core.A strong correlation was found between the ability to perform retting and the degradation of sparsely esterified pectin, a substrate of polygalacturonase. This led to the conclusion that polygalacturonase plays a key role in the enzymatic retting of flax. We purified and characterized an extracellular polygalacturonase produced by Rhizopus oryzae, a very potent retting organism. The purified enzyme which appeared to be the single active component in retting, has non-methylated polygalacturonan as its preferred substrate. Peptide sequences indicate that the enzyme, like another polygalacturonase (EC. 3.2.1.15), belongs to glycosyl hydrolase family 28. It contains, however, an N-terminal sequence absent from other fungal pectinases, but present in an enzyme from the phytopathogenic bacterium, Ralstonia solanacearum.Our finding that removal of calcium ions from the plant material by pre-incubation in dilute acid in enzymatic retting could reduce enzyme consumption by several orders of magnitude, improves the economical feasibility of the enzymatic retting process. Comparisons with different acids showed that the action was mainly pH dependent.Pectinases were employed as analytical tools in a study of stored wood discoloration and, together with cellulases, in a mechanical process for making pulp from flax and hemp in paper production.
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| 16. |
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| 17. |
- Zhang, Jing, et al.
(author)
-
Polygalacturonase is the key component in enzymatic retting of flax
- 2000
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In: Journal of Biotechnology. - 0168-1656 .- 1873-4863. ; 81:1, s. 85-89
-
Journal article (peer-reviewed)abstract
- Seven commercial enzyme mixtures were tested for their ability to perform retting of flax (i.e. to separate flax fibers by partly removal of middle lamella) and were assayed for hydrolysis of xylan, cellulose and four kinds of pectin. The only activity that showed correlation to the ability to perform retting was the degradation of low esterfied pectin. A purified Aspergillus niger polygalacturonase was also shown to be able to perform retting. From this data it is hypothesized that degradation of the smooth regions (i.e. non-methylated polygalacturonase) in the middle lamella pectin is the most important step in enzymatic retting.
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| 18. |
- Zhang, J., et al.
(author)
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The active component in the flax-retting system of the zygomycete Rhizopus otyzae sb is a family 28 polygalacturonase
- 2005
-
In: Journal of Industrial Microbiology & Biotechnology. - : Oxford University Press (OUP). - 1367-5435 .- 1476-5535. ; 32:10, s. 431-438
-
Journal article (peer-reviewed)abstract
- The zygomycete Rhizopus oryzae sb is a very efficient organism for retting of flax, the initial microbiological step in the process of making linen. An extracellular polygalacturonase, when isolated could perform retting, and therefore probably is the key component in the retting system of R. oryzae. This was purified and characterized. The purified enzyme has a molecular mass of 37,436 Da from mass spectrometric determination, an isoelectric point of 8.4, and has non-methylated polygalacturonic acid as its preferred substrate. Peptide sequences indicate that the enzyme belongs to family 28, in similarity with other polygal-acturonases (EC. 3.2.1.15). It contains, however an N-terminal sequence absent in other fungal pectinases, but present in an enzyme from the phytopathogenic bacterium Ralstonia solanacearum. The biochemical background for the superior retting efficiency of R. oryzae sb is discussed.
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| 19. |
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| 20. |
- Abbadessa, Anna, et al.
(author)
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Characterization of Two Novel Bio-based Materials from Pulping Process Side Streams : Ecohelix and CleanFlow Black Lignin
- 2018
-
In: BioResources. - : NORTH CAROLINA STATE UNIV DEPT WOOD & PAPER SCI. - 1930-2126. ; 13:4, s. 7606-7627
-
Journal article (peer-reviewed)abstract
- The characteristics of two novel types of technical lignin, namely Ecohelix (EH) and CleanFlow black lignin (CFBL), isolated from two different pulping process side streams, were analyzed. EH and CFBL were analyzed in terms of general composition, chemical functionalities, molar mass distribution, and thermal stability. For comparison, two relevant types of commercially available lignosulfonate and kraft lignin were used. The results showed that EH contains a large amount of sulfonated lignin, together with carbohydrates and ash. As such, it can be considered a lignin-carbohydrate hybrid molecule. CFBL was found to contain 91.5% Klason lignin and the lowest amount of carbohydrates (0.3%). EH showed the highest content of aliphatic OH groups (5.44 mmol/g) and CFBL a high content of phenols (4.73 mmol/g). EH had a molecular weight of 31.4 kDa and a sufficient thermal stability. CFBL had the lowest molecular weight (M-w = 2.0 kDa) and thermal stability of all kraft lignins analyzed in this study. These properties highlighted that EH is a suitable building block for material development and that CFBL is a promising material for the production of biofuel and biochemicals.
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| 21. |
- Abbadessa, Anna, et al.
(author)
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Layer-by-layer assembly of sustainable lignin-based coatings for food packaging applications
- 2023
-
In: Progress in organic coatings. - : Elsevier BV. - 0300-9440 .- 1873-331X. ; 182
-
Journal article (peer-reviewed)abstract
- Packaging plays a critical role in ensuring food safety and shelf life by protecting against e.g., moisture, gases, and light. Polyethylene (PE) is widely used in food packaging, but it is mainly produced from non-renewable resources and it is an inefficient oxygen and light barrier. In this study, the layer-by-layer (LbL) assembly of a sustainably produced lignin-based polymer (EH) with polyethylenimine (PEI) or chitosan (CH) was used to fabricate (partially or fully) bio-based coatings with the aim of improving barrier properties of PE films. The charge density of EH was calculated using a polyelectrolyte titration method and the hydrodynamic diameters of EH, PEI and CH were determined by Dynamic Light Scattering (DLS). LbL assembly was monitored in situ via Quartz Crystal Microbalance with Dissipation (QCM-D) and Stagnation Point Adsorption Reflectometry (SPAR). PE films were coated with a variable number of PEI/EH or CH/EH bilayers (BL) using an immersive LbL assembly method. Coated films were studied in terms of light-blocking ability, wettability, thermal behaviour, surface structure, as well as oxygen and water vapor barrier properties. QCM-D and SPAR data showed a stepwise multilayer formation and strong interactions between the oppositely charged polymers, with PEI/EH coating having a greater amount of deposited polymer compared to CH/EH coating at the same number of BL. Overall, light barrier properties and wettability of the coated films increased with the number of deposited bilayers. Coated PE films maintained the overall thermal behaviour of PE. A number of BL of 20 was found to be the most promising based on the studied properties. Selected samples showed improved oxygen and water vapor barrier properties, with PEI/EH coating performing better than CH/EH coating. Taken altogether, we demonstrated that a novel and sustainable lignin-based polymer can be combined with PEI or CH to fabricate (partially or fully) bio-based coatings for food packaging.
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| 22. |
- Akin, Danny E., et al.
(author)
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Progress in enzyme-retting of flax
- 2004
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In: Journal of Natural Fibers. - 1544-0478. ; 1:1, s. 21-47
-
Journal article (peer-reviewed)abstract
- New methods for retting flax are sought to overcome problems in the current method of dew-retting of flax. Published data are reviewed and new data presented on the development and testing of a method to ret flax using pectinase-rich enzyme mixtures plus chelators based on cost and fiber yield and properties. In spray enzyme retting (SER), flax stems are crimped to physically disrupt the plant's protective barrier and then sprayed until soaked with, or briefly immersed in, an enzyme/ chelator formulation. Flax is then incubated at temperatures optimal for enzyme activity, washed, and dried. Pilot scale tests, conducted with 10 kg samples of flax retted with a series of formulations, showed that this method effectively retted flax stems from a variety of sources, including fiber flax, mature fiber flax, and linseed straw. Fiber yield, strength, and fineness were significantly influenced by variations in enzyme-chelator amounts. Cellulases in pectinase mixtures appeared to preferentially attack dislocations in fibers and fiber bundles resulting in loss of fiber strength. Polygalacturonases alone effectively separated fiber from non-fiber components. The SER method proved to be an effective framework for further tests on enzyme-chelator formulations that now must be integrated with physical processing to optimize the extraction of flax fibers based on cost and fiber yield and properties.
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| 23. |
- Alexandersson, Gunnar, et al.
(author)
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Coopetition between commercial and subsidized railway services : The case of the greater Stockholm region
- 2018
-
In: Research in Transportation Economics. - : Elsevier. - 1875-7979 .- 0739-8859. ; 69:SI, s. 349-359
-
Journal article (peer-reviewed)abstract
- An important ingredient of the Swedish railway system is the increased involvement of public actors in the provision of local and regional railway services. The local and regional railway services show the strongest growth of all market segments in the Swedish passenger railway market. The strong growth is due both to changes in travel patterns and improved subsidized railway services. One important factor in the success of the regional public transport authorities’ (PTA) railway services is the redefinition of the scope of these railway services by interconnecting regional railway networks into bigger entities.In 2017, nearly all local and regional railway services in Sweden's most populated region, Mälardalen, became part of a network of railway services subsidized by the PTAs in the greater region. We analyse the cooperative and competitive interactions between the stakeholders in the greater region using the key concepts in the theory of hybrid organizations. We find that despite moving towards a unified public transport market covering many counties the hybrid organizations use different governance structures and have different principles for sharing value creation. The closer cooperation paradoxically enhances competition in the regional railway market, both between subsidized travel cards and between subsidized and commercial railway services.
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| 24. |
- Alexandersson, Gunnar, et al.
(author)
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Coping with unforeseen circumstances : The COVID-19 crisis and bus contract renegotiation in Sweden
- 2024
-
In: Journal of Industrial and Business Economics. - : Springer Nature. - 1972-4977 .- 0391-2078.
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Journal article (peer-reviewed)abstract
- In principle, competitively tendered contracts in Swedish public bus transport are not supposed to be renegotiated during the contract period. In practice, it happens quite frequently. The need for renegotiations became evident during the COVID-19 crisis. This external shock to the system was unusually strong. Demand for bus services dropped abruptly, affecting revenues of procuring authorities and, depending on contract type, also bus operators. To make the situation even worse, costs typically remained constant, as frequent services were supposed to be upheld to avoid the spreading of the virus in crowded buses. Contract renegotiations during the COVID-19 crisis were clearly caused by unexpected exogenous events. Contracts with passenger incentives, linking a substantial part of compensation to the number of passengers, have been more likely to be renegotiated than gross-cost contracts, which were easier to adjust to the drop in demand. Typically, renegotiations were triggered by operators. While being a pragmatically rational response to an extreme situation, the renegotiations and their outcome may not in all cases have been compliant with the legal framework for public procurements, even when taking into account the exemptions made possible by the framework. In cases where passenger incentive contracts have been transformed into gross-cost contracts it could be argued that the nature of the contract has been changed. A new tender should then probably have been performed instead, although this has not been tried in court. The COVID-19 crisis could have long-term impact on contracts and procurements in the industry, affecting how effective competition will be in future tenders. For now, gross-cost contracts seem to be the norm, and it is possible that passenger-incentive contracts will become less common overall. One way to handle unexpected events with profound impact could be to include so-called threat-points that trigger renegotiation of a contract.
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| 25. |
- Aminzadeh, Selda, et al.
(author)
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A possible explanation for the structural inhomogeneity of lignin in LCC networks
- 2017
-
In: Wood Science and Technology. - : SPRINGER. - 0043-7719 .- 1432-5225. ; 51:6, s. 1365-1376
-
Journal article (peer-reviewed)abstract
- Lignin has a very complex structure, and this is partly due to the monomers being connected by many different types of covalent bonds. Furthermore, there are multiple covalent bonds between lignin and polysaccharides in wood, and it is known that the structure of lignin covalently bound to the hemicellulose xylan is different to lignin bound to the hemicellulose glucomannan. Here, synthetic lignin (DHP) is synthesized at different pH and it is shown that lignin made at lower pH has a structure more similar to the lignin bound to xylan, i.e., having higher relative content of beta-O-4 ethers. It is hypothesized that xylan due to its carboxylic acids forms a locally lower pH and thus "direct" the lignin structure to have more beta-O-4 ethers. The biological significance of these results is discussed.
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| 26. |
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| 27. |
- Andersson, Alexander, et al.
(author)
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Presence of Calcium Cations Stimulate Alkaline Hydrolysis of Cellulose During Kraft Pulping Conditions
-
Other publication (other academic/artistic)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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| 28. |
- Antonsson, Stefan, et al.
(author)
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Adding lignin derivatives to decrease the effect of mechano-sorptive creep in linerboard
- 2008
-
In: Appita journal. - 1038-6807. ; 61:6, s. 468-471
-
Journal article (peer-reviewed)abstract
- When load is applied to any type of paper while varying the relative humidity, the paper will creep more than if the same load is applied at constant humidity. This behaviour is called mechano-sorptive creep or accelerated creep, and the reasons for its occurrence in paper are still not fully understood. However, wet strength and the addition of apolar (hydrophobic) compounds to sheets have previously been suggested as factors improving the mechano-sorptive creep performance. This work evaluates a method for improving wet strength and tests the addition of a hydrophobic compound, with particular reference to mechano-sorptive creep stiffness. Wet strength was improved by subjecting kraft liner pulp to low-molecular-weight lignin, obtained by cross-flow filtration, and to the radical initiator manganese(III). The hydrophobic compound added was a suberin-like lignin derivative. Adding the suberin-like lignin derivative significantly increased the mechano-sorptive creep stiffness, even though the stiffness at 90% rh decreased in the tested samples. This was probably because of the decrease in hygroexpansion caused by this hydrophobic additive. Even though it is possible significantly to increase the wet strength of kraft liner pulp by adding manganese(III) and cross-flow-filtered lignin, doing so has no significant effect on mechano-sorptive creep stiffness.
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| 29. |
- Antonsson, Stefan, et al.
(author)
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Biomimetic synthesis of suberin for new biomaterials
- 2005
-
In: Appita Annual Conference. ; , s. 561-564
-
Conference paper (peer-reviewed)abstract
- Suberin is the biopolymer giving cork (oak bark) its hydrophobic and resistant characteristics. It acts as a diffusion barrier in bark and roots of plants. Similarly to lignin, it is a phenolic polymer with good affinity to cellulose and other wood polysaccharides, but it also contains polyaliphatic and strongly hydrophobic elements. In order to produce a lignin derivative similar to suberin, a desired lignin starting material should be of low molecular weight and have a high content of hydroxylic phenolic groups. By means of cross flow nanofiltration of softwood kraft pulping black liquor and pH-precipitation with diluted sulphuric acid, such a lignin has been obtained. Due to the fact that too much organics entering the recovery boiler frequently is the bottleneck for pulp production increases, a removal of part of the lignin can be economically very favourable. By using this lignin together with linola oil, a linseed oil with a large amount of unsaturated structures, an attempt was made to create a new hydrophobic lignin derivative similar tosuberin. The product was analysed with FT-IR, Fourier Transformed Infra Red Spectroscopy and GPC, Gel Permeation Chromatography. The suberin like material obtained from this lignin could be polymerised on thermo mechanical pulp fibres by means of Mn(III)-driven phenolic coupling. The ability of the suberin monomers to act as a hydrophobic paper coating was evaluated with contact angle measurements and the results indicate that this lignin derivative was potentially of interest due to its capability to interact well with wood fibres and make paper hydrophobic.
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| 30. |
- Antonsson, Stefan, et al.
(author)
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Low Mw-lignin fractions together with vegetable oils as available oligomers for novel paper-coating applications as hydrophobic barrier
- 2008
-
In: Industrial crops and products (Print). - : Elsevier BV. - 0926-6690 .- 1872-633X. ; 27:1, s. 98-103
-
Journal article (peer-reviewed)abstract
- Lignin residues are available in large amounts as kraft lignin from chemical pulping processes. This lignin is mainly incinerated in recovery boilers. The recovery boilers are often the bottle-necks in the overall pulping process when pulp production increases are desired. Through cross-flow nano-filtration of the black liquor from kraft pulping, a low-molecular weight lignin fraction can be removed thus decreasing the organic load on the recovery boilers. The low-molecular weight lignin fraction furthermore exhibit different characteristics compared to other commercial kraft lignins and represents a new raw material source in novel applications. The low-molecular weight lignin was used together with a vegetable oil to produce a new hydrophobic lignin derivative similar to suberin. The lignin and the lignin derivative was analysed with FT-IR, UV-vis and SEC. The ability of the product to make paper surfaces hydrophobic was also evaluated. The results demonstrate the possibility to make a suberin-like lignin derivative that is potentially of interest in paper-coating applications due to its capability to interact well with wood fibres and make paper hydrophobic.
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| 31. |
- Antonsson, Stefan, 1979-
(author)
-
Strategies for improving kraftliner pulp properties
- 2008
-
Doctoral thesis (other academic/artistic)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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| 32. |
- Antonsson, Stefan, et al.
(author)
-
The influence of lignin and xylan on some kraftliner pulp properties
- 2009
-
In: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 24:4, s. 403-408
-
Journal article (peer-reviewed)abstract
- This study investigates the influence of lignin and hemicellulose content on the mechanical and physical properties of softwood kraft liner pulp. Tensile properties, hygroexpansion, and mechano-sorptive creep properties were measured. The lignin and hemicellulose contents were modified by chlorite delignification and xylanase treatment. After treatment, the chemical composition of the pulps was 3-14% Klason lignin, 69-77% cellulose, 16-21% hemicellulose, and 4-7% xylan. In the tested pulps, low lignin content tended to decrease hygroexpansion as well as increase tensile stiffness and mechano-sorptive creep stiffness. Xylan contributed less to the pulp sheet properties, but at equal lignin contents, higher xylan content tended to give increased hygroexpansion and worse mechano-sorptive creep properties.
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| 33. |
- Antonsson, Stefan, 1979-
(author)
-
The Use of Lignin Derivatives to Improve Selected Paper Properties
- 2007
-
Licentiate thesis (other academic/artistic)abstract
- Ved består huvudsakligen av tre typer av polymerer, cellulosa, hemicellulosa och lignin. Lignin bildas i naturen genom enzymatiskt initierad oxidativ koppling av tre olika typer av fenylpropan-enheter. Dessa bygger genom olika kol-kol- och kol-syre-bindningar upp en amorf tredimensionell polymer. När kemisk massa tillverkas bryts lignin ner och löses ut i kokluten. Luten innehåller de förbrukade kokkemikalierna och bränns generellt i en sodapanna för att regenerera kemikalierna och producera ånga. Sodapannan är emellertid dyr. Därför har den blivit produktionsbegränsande på många massabruk. Att avlägsna en del av ligninet från avluten vore därför önskvärt och att finna ekonomiskt intressanta produkter baserade på lignin från svartlut är därför ett viktigt forskningsområde . Ett lämpligt område för ligninprodukter vore som tillsatts i oblekt massa. Oblekt massa används till stor del för tillverkning av kraftliner, topp- och bottenskikten på wellpapp. När lådor av wellpapp lagras i containrar som färdas över haven, förändras den relativa luftfuktigheten. Detta gör att lådorna kollapsar lättare än om de skulle ha lagrats vid konstant luftfuktighet, även en hög sådan. Detta är på grund av det så kallade mekanosorptiva- eller accelererade krypfenomenet. Genom tillsatts av våtstyrkemedel till kraftliner eller behandla den med hydrofoba ämnen, finns indikatoner på att mekanosorptiva effekten skulle kunna minska. För att försöka minska den effekten har ett lågmolekylärt kraftlignin, som utvunnits med hjälp av tvärsflödesfiltrering av svartlut och svavelsyrafällning, använts. Genom derivatisering av detta lignin med linolja erhölls ett hydrofobt ligninderivat som uppvisar strukturella likheter med biopolymeren suberin. När detta suberinlika ligninderivat tillsätts till massa verkar det mekanosorptiva krypet minska. När lågmolekylärt lignin används tillsammans med ligninradikalinitiatorerna lackas eller mangan(III) i kraftlinermassa erhålls dessutom en våtstyrka på ca 5% av torrstyrkan. Efter aminering av detta lignin gav en tillsatts till kraftlinermassan en våtstyrka på upp till 10% av torrstyrkan. Det finns indikationer på att det mekanosorptiva krypet samtidigt minskar när dessa behandlingar görs som ger upphov till ökad våtstyrka.
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| 34. |
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| 35. |
- Anukam, Anthony, et al.
(author)
-
A review of the mechanism of bonding in densified biomass pellets
- 2021
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In: Renewable & sustainable energy reviews. - : Elsevier. - 1364-0321 .- 1879-0690. ; 148
-
Journal article (peer-reviewed)abstract
- The production of durable biomass pellets have always been challenged by several factors including the lack of understanding of the mechanism involved in how particles combine to form pellets under standard conditions of the pellet press. This is because contributing factors span several molecular, microscopic, and even nanoscopic levels as biomass undergoes pelleting. The characteristics of the bonds formed between the combining particles and their relevance to the quality of pellets remains vague, no matter how quality is defined. However, even though few researchers have attempted to explain the mechanism of bonding in densified biomass pellets using different theories, none of their hypotheses supports particle bonding from a structural chemistry perspective. There are still no clear explanations which consider the role of molecular structure and the interactions of substances as milled biomass undergo pelleting. In view of these arguments therefore, this review presents an in-depth analysis of a structural chemistry perspective of the mechanism of bonding and the use of additives in densified biomass pellets and helps identify research areas needed to facilitate better understanding of bonding in densified biomass pellets. The status of current research in biomass pelleting, types of materials suitable as additives and their structural characteristics, as well as the current technical specifications of using additives are also discussed.
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| 36. |
- Areskogh, Dimitri, et al.
(author)
-
Fenton's reaction : a simple and versatile method to structurally modify commercial lignosulphonates
- 2011
-
In: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 26:1, s. 90-98
-
Journal article (peer-reviewed)abstract
- Treatment of lignosulphonates with hydrogen peroxide and Fe (II) acetate under mild conditions can be used to increase the molecular weight and content of carboxylic acids. Such Fenton's oxidation can produce, in some of the conditions of and lignosulphonate concentration, a two-fold increase in the molecular weight and a 6-7 fold increase in the carboxylic acid content. The structural modifications of lignosulphonate may increase the technical performance of the product in several applications. Possible reaction mechanisms of the Fenton system are proposed and discussed.
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| 37. |
- Areskogh, Dimitri, et al.
(author)
-
Immobilisation of laccase for polymerisation of commercial lignosulphonates
- 2011
-
In: Process Biochemistry. - : Elsevier BV. - 1359-5113 .- 1873-3298. ; 46:5, s. 1071-1075
-
Journal article (peer-reviewed)abstract
- The oxidoreductive enzyme laccase has previously been shown to be able to increase the average molecular weight of lignosulphonatesthrough generation of phenoxy radicals on end groups and the subsequent radical-radical coupling reactions that cross-link individual lignosulphonate molecules. Utilisation of laccases for this purpose is a potential industrial process not only to improve the properties of technical lignosulphonates but also to expand their utilisation to new areas. Immobilisation of the laccase is an interesting technique to enable reusage of the enzyme and thus reduce costs involved with such process. In this work, we demonstrate the potential of immobilised laccase to polymerise technical lignosulphonates. A number of factors that limits re-utilisation of the immobilised catalyst such as lignosulphonate adsorption onto the carrier and laccase deactivation have been identified and are discussed. However, by using a low-porosity support and lower reaction temperatures these problems can be limited.
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| 38. |
- Areskogh, Dimitri, et al.
(author)
-
Investigation of the Molecular Weight Increase of Commercial Lignosulfonates by Laccase Catalysis
- 2010
-
In: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 11:4, s. 904-910
-
Journal article (peer-reviewed)abstract
- Lignosulfonates are by-products from the sulfite pulping process. During this process, lignin is liberated from pulp fibers through sulfonation and washed away. As a consequence, the lignosulfonate molecules contain both hydrophobic and hydrophilic moieties. Lignosulfonates are low-value products with limited performance and are used as such as binders, surfactants, and plasticizers in concrete. Lignosulfonates face strong competition from synthetic petroleum-based plasticizers with superior quality. Therefore, increasing the performance of lignosulfonates is desirable not only from a sustainability point of view but also to expand their usage. One important aspect that describes how well lignosulfonates can act as plasticizers is the molecular weight. In this paper, the molecular weight of four commercial lignosulfonates is increased through oxidation by two laccases without utilization of mediators. Different parameters to obtain maximal molecular weight increase were identified and the technical significance of the experiments is discussed.
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| 39. |
- Areskogh, Dimitri, et al.
(author)
-
Oxidative polymerisation of models for phenolic lignin end-groups by laccase
- 2010
-
In: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 64:1, s. 21-34
-
Journal article (peer-reviewed)abstract
- The redox enzyme laccase can lead to cross-linking of lignin molecules by oxidising phenolic end groups to resonance-stabilised radicals that can undergo radical coupling to form covalent bonds. This property has potential for many technical applications. However, laccase treatment can also lead to degradation. Experiments were performed with two laccases of different oxidation potential and pH and temperature optima. The predominant reaction following laccase oxidation is the formation of 5-5' and 4-O-5' bonds. If the 5-position is blocked, other reactions occur, including coupling of the 1-position and oxidation of the a-position, which aggravates cross-linking of different lignin molecules. The product profile generated by the two laccases is somewhat different, mainly because of the different pH rather than differences in enzyme activity. Reaction mechanisms and the technical and biological significance of the results are discussed.
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| 40. |
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| 41. |
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| 42. |
- Areskogh, Dimitri, et al.
(author)
-
Structural modification of commercial lignosulphonates through laccase catalysis and ozonolysis
- 2010
-
In: Industrial crops and products (Print). - : Elsevier BV. - 0926-6690 .- 1872-633X. ; 32:3, s. 458-466
-
Journal article (peer-reviewed)abstract
- Lignosulphonates are by-products from the sulphite pulping process, in which lignin is separated from cellulose by the addition of sulphonic acid groups to the alpha-position of lignin, thereby increasing the solubility of lignin in water. The predominant industrial utilisations of lignosulphonates are as dispersants, plasticisers and water-reducing agents in concrete preparation. The ability of lignosulphonates to function as a good plasticisers and water reducers is intimately linked with the purity of the lignosulphonate, its molecular weight and the number of charged groups present in the macromolecule. Currently, lignosulphonates are outrivaled by synthetic plasticisers termed superplasticisers due to their superior properties when used as additives to high-strength concrete. If lignosulphonates are to successfully compete with these superplasticisers, significant modifications are required. This paper describes a two-stage treatment of lignosulphonates in which the molecular weight is increased through laccase oxidation and carboxylic groups are introduced through ozonolysis. The technical significance of the results is also discussed.
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| 43. |
- Areskogh, Dimitri, 1982-
(author)
-
Structural Modifications of Lignosulphonates
- 2011
-
Doctoral thesis (other academic/artistic)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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| 44. |
- Areskogh, Dimitri, et al.
(author)
-
Sulfonation of phenolic end groups in lignin directs laccase-initiated reactions towards cross-linking
- 2010
-
In: Industrial Biotechnology. - : Mary Ann Liebert Inc. - 1550-9087 .- 1931-8421. ; 6:1, s. 50-59
-
Journal article (peer-reviewed)abstract
- The effect of sulfonation of the a-carbon on model compounds representing phenolic end groups on lignin was studied with respect to the reactions initiated by oxidation of laccase, by mass spectrometry. Sulfonation seems to direct the reactions towards formation of 5-5´ and 4-O-5´ bonds, avoiding formation of 1-O-4´ bonds and oxidation of the a-carbon. This, in turn, will facilitate cross-linking reactions between lignin molecules. Sulfonation therefore has potential as an industrial pretreatment prior to laccase treatment for various wood-containing materials.
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| 45. |
- Argyropoulos, Dimitris D. S., et al.
(author)
-
Kraft Lignin: A Valuable, Sustainable Resource, Opportunities and Challenges
- 2023
-
In: ChemSusChem. - : John Wiley and Sons Inc. - 1864-5631 .- 1864-564X. ; 16:23
-
Research review (peer-reviewed)abstract
- Kraft lignin, a by-product from the production of pulp, is currently incinerated in the recovery boiler during the chemical recovery cycle, generating valuable bioenergy and recycling inorganic chemicals to the pulping process operation. Removing lignin from the black liquor or its gasification lowers the recovery boiler load enabling increased pulp production. During the past ten years, lignin separation technologies have emerged and the interest of the research community to valorize this underutilized resource has been invigorated. The aim of this Review is to give (1) a dedicated overview of the kraft process with a focus on the lignin, (2) an overview of applications that are being developed, and (3) a techno-economic and life cycle asseeements of value chains from black liquor to different products. Overall, it is anticipated that this effort will inspire further work for developing and using kraft lignin as a commodity raw material for new applications undeniably promoting pivotal global sustainability concerns.
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| 46. |
- Azhar, Shoaib, et al.
(author)
-
Chemoenzymatic separation of softwood polymers
- 2011
-
In: Proceedings of the 16th international symposium of wood, fiber and pulp chemistry. - 9787501982066 ; , s. 932-936
-
Conference paper (peer-reviewed)abstract
- Spruce wood chips were chemically pre-treated with sodium hydroxide to open up the compact structure of wood. The wood was then treated with enzymes (xylanase, gamanase and mannanase) and subjected to extraction with a mixture of methanol and alkali to efficiently isolate lignin and hemicelluloses. Chemical pre-treatment improved enzyme efficiency which consequently enhanced the extraction of lignocelluloses with higher average molar mass than the references.
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| 47. |
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| 48. |
- Azhar, Shoaib, 1980-, et al.
(author)
-
Extraction of hemicelluloses from fiberized spruce wood
- 2015
-
In: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 117, s. 19-24
-
Journal article (peer-reviewed)abstract
- A novel mechanical pre-treatment method was used to separate the wood chips into fiber bundles in order to extract high molecular weight wood polymers. The mechanical pre-treatment involved chip compression in a conical plug-screw followed by defibration in a fiberizer. The fiberized wood was treated with hot water at various combinations of time and temperature in order to analyze the extraction yield of hemicelluloses at different conditions. Nearly 6 mg/g wood of galactoglucomannan was obtained at 90◦C/120min which was about three times more than what could be extracted from wood chips. The extracted carbohydrates had molecular weight ranging up to 60 kDa. About 10% of each of the extracted material had a molecular weight above 30 kDa. The extraction liquor could also be reused for consecutive extractions with successive increase in the extraction yield of hemicelluloses.
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| 49. |
- Azhar, Shoaib, et al.
(author)
-
Extraction of polymers from enzyme-treated softwood
- 2011
-
In: BioResources. - 1930-2126. ; 6:4, s. 4606-4614
-
Journal article (peer-reviewed)abstract
- In a biorefinery context it is an advantage to fractionate and extract different wood components in a relatively pure form. However, one major obstacle for efficient extraction of wood polymers (lignin, polysaccharides etc.) is the covalent lignin-polysaccharide networks present in lignified cell walls. Enzymatic catalysis might be a useful tool for a controlled degradation of these networks, thereby enhancing the extraction of high molecular weight polymers. In this work, a methanol-alkali mixture was used to extract two different wood samples treated with endoxylanase and gammanase, respectively. Wood chips were pretreated with alkali prior to enzymatic treatment to enhance the cell-wall accessibility to enzymes. Extractions were also carried out on non-enzyme-treated samples to evaluate the enzymatic effects. Results showed that the enzymatic treatment increased the extraction yield, with gammanase as the more efficient of the two enzymes. Furthermore, polymers extracted from xylanase-treated wood had a higher degree of polymerization than the reference.
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| 50. |
- Backman, Dan, 1972-
(author)
-
Interaction Studies of Secreted Aspartic Proteases (Saps) from Candida albicans : Application for Drug Discovery
- 2005
-
Doctoral thesis (other academic/artistic)abstract
- This thesis is focused on enzymatic studies of the secreted aspartic proteases (Saps) from Candida albicans as a tool for discovery of anti-candida drugs. C. albicans causes infections in a number of different locations, which differ widely in the protein substrates available and pH. Since C. albicans needs Saps during virulent growth, these enzymes are good targets for drug development.In order to investigate the catalytic characteristics of Saps and their inhibitor affinities, substrate-based kinetic assays were developed. Due to the low sensitivity of these assays, especially at the sub-optimal pH required to mimic the different locations of infections, these assays were not satisfactory. Therefore, a biosensor assay was developed whereby, it was possible to study interaction between Saps and inhibitors without the need to optimise catalytic efficacy. Furthermore, the biosensor assay allowed determination of affinity, as well as the individual association and dissociation rates for inhibitor interactions.Knowledge about substrate specificity, Sap subsite adaptivity, and the pH dependencies of catalytic efficacy has been accumulated. Also, screening of transition-state analogue inhibitors designed for HIV-1 protease has revealed inhibitors with affinity for Saps. Furthermore, the kinetics and pH dependencies of their interaction with Saps have been investigated. One of these inhibitors, BEA-440, displayed a complex interaction with Saps, indicating a conformational change upon binding and a very slow dissociation rate. A time dependent interaction was further supported by inhibition measurements. The structural information obtained affords possibilities for design of new more potent inhibitors that might ultimately become drugs against candidiasis. The strategy to combine substrate specificity studies with inhibitor screening has led to complementary results that generate a framework for further development of potent inhibitors.
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