| 1. |
- Kjellander, Marcus
(författare)
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Nanoporous Aluminum Oxide – A Promising Support for Modular Enzyme Reactors
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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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| 2. |
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| 3. |
- Areskogh, Dimitri, et al.
(författare)
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Fenton's reaction : a simple and versatile method to structurally modify commercial lignosulphonates
- 2011
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Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 26:1, s. 90-98
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Tidskriftsartikel (refereegranskat)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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| 4. |
- Areskogh, Dimitri, et al.
(författare)
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Immobilisation of laccase for polymerisation of commercial lignosulphonates
- 2011
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Ingår i: Process Biochemistry. - : Elsevier BV. - 1359-5113 .- 1873-3298. ; 46:5, s. 1071-1075
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Tidskriftsartikel (refereegranskat)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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| 5. |
- Areskogh, Dimitri, et al.
(författare)
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Investigation of the Molecular Weight Increase of Commercial Lignosulfonates by Laccase Catalysis
- 2010
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 11:4, s. 904-910
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Tidskriftsartikel (refereegranskat)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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| 6. |
- Areskogh, Dimitri, et al.
(författare)
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Oxidative polymerisation of models for phenolic lignin end-groups by laccase
- 2010
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 64:1, s. 21-34
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Tidskriftsartikel (refereegranskat)abstract
- The redox enzyme laccase can lead to cross-linking of lignin molecules by oxidising phenolic end groups to resonance-stabilised radicals that can undergo radical coupling to form covalent bonds. This property has potential for many technical applications. However, laccase treatment can also lead to degradation. Experiments were performed with two laccases of different oxidation potential and pH and temperature optima. The predominant reaction following laccase oxidation is the formation of 5-5' and 4-O-5' bonds. If the 5-position is blocked, other reactions occur, including coupling of the 1-position and oxidation of the a-position, which aggravates cross-linking of different lignin molecules. The product profile generated by the two laccases is somewhat different, mainly because of the different pH rather than differences in enzyme activity. Reaction mechanisms and the technical and biological significance of the results are discussed.
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| 7. |
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| 8. |
- Areskogh, Dimitri, et al.
(författare)
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Structural modification of commercial lignosulphonates through laccase catalysis and ozonolysis
- 2010
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Ingår i: Industrial crops and products (Print). - : Elsevier BV. - 0926-6690 .- 1872-633X. ; 32:3, s. 458-466
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Tidskriftsartikel (refereegranskat)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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| 9. |
- 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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| 10. |
- Areskogh, Dimitri, et al.
(författare)
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Sulfonation of phenolic end groups in lignin directs laccase-initiated reactions towards cross-linking
- 2010
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Ingår i: Industrial Biotechnology. - : Mary Ann Liebert Inc. - 1550-9087 .- 1931-8421. ; 6:1, s. 50-59
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Tidskriftsartikel (refereegranskat)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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| 11. |
- Azhar, Shoaib, et al.
(författare)
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Chemoenzymatic separation of softwood polymers
- 2011
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Ingår i: Proceedings of the 16th international symposium of wood, fiber and pulp chemistry. - 9787501982066 ; , s. 932-936
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Konferensbidrag (refereegranskat)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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| 12. |
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| 13. |
- Azhar, Shoaib, et al.
(författare)
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Extraction of polymers from enzyme-treated softwood
- 2011
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Ingår i: BioResources. - 1930-2126. ; 6:4, s. 4606-4614
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Tidskriftsartikel (refereegranskat)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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| 14. |
- Bi, Ran, et al.
(författare)
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Isolation and identification of microorganisms from soil able to ive on lignin as carbon source and produce enzymes that cleave beta-O-4mbond in lignin
- 2011
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Ingår i: Cellulose Chemistry and Technology. - 0576-9787.
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Tidskriftsartikel (refereegranskat)abstract
- Twenty one strains of micro organism from Scandinavian soil had been isolated that could utilize lignin as only carbon source and 11 strains of them were identified. Different types of technical lignins were used.5 faster growing strains were cultivated in shaking flask cultures with ligninosulfonate as sole carbon source,and lignin appeared to be consumed after several days while mycelia was observed accumulated.Cell free filtrates of the 5 faster growing strains could lower the apparent molecular weights of lignosulphonates and the culture filtrate of one strain could cleave the lignin model compound with.The significances of the results are discussed.
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| 15. |
- Bi, Ran, et al.
(författare)
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Isolation and identification of microorganisms from soil able to live on lignin as a carbon source and to produce enzymes which cleave beta-O-4 bond in a lignin model compound
- 2012
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Ingår i: Cellulose Chemistry and Technology. - 0576-9787. ; 46:3-4, s. 227-242
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Tidskriftsartikel (refereegranskat)abstract
- Several strains of fungi were isolated and identified from Scandinavian soil using agar plates with lignin as a carbon source. The strains grew significantly faster on this medium than on control plates without lignin. Different types of technical lignins were used, some of which contained trace amounts of sugars, even if the increased growth rate seemed not related to the sugar content. Some strains were cultivated in shaking flask cultures with lignin as a carbon source, with lignin apparently consumed by microbes - while accumulation of the microorganism biomass occurred. The cell-free filtrates of these cultures could reduce the apparent molecular weights of lignosulphonates, while the culture filtrate of one strain could cleave the beta-O-4 bond in a lignin model compound.
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| 16. |
- Bi, Ran, 1985-, et al.
(författare)
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Isolation and identification of microorganisms from soil able to live on lignin as acarbon source and to produce enzymes which cleave the β-o-4 bond in a lignin model compound
- 2012
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Ingår i: Cellulose Chemistry and Technology. - : UBC. - 0576-9787. ; 46:3-4, s. 227-242
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Tidskriftsartikel (refereegranskat)abstract
- Several strains of fungi were isolated and identified from Scandinavian soil using agar plates with lignin as a carbon source. The strains grew significantly faster on this medium than on control plates without lignin. Different types of technical lignins were used, some of which contained trace amounts of sugars, even if the increased growth rate seemed not related to the sugar content. Some strains were cultivated in shaking flask cultures with lignin as a carbon source, with lignin apparently consumed by microbes - while accumulation of the microorganism biomass occurred. The cell-free filtrates of these cultures could reduce the apparent molecular weights of lignosulphonates, while the culture filtrate of one strain could cleave the beta-O-4 bond in a lignin model compound.
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| 17. |
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| 18. |
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| 19. |
- Guerra, Lina, et al.
(författare)
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Myc is required for activation of the ATM-dependent checkpoints in response to DNA damage
- 2010
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Ingår i: PLOS ONE. - : Public Library Science. - 1932-6203. ; 5:1
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: The MYC protein controls cellular functions such as differentiation, proliferation, and apoptosis. In response to genotoxic agents, cells overexpressing MYC undergo apoptosis. However, the MYC-regulated effectors acting upstream of the mitochondrial apoptotic pathway are still unknown.PRINCIPAL FINDINGS: In this study, we demonstrate that expression of Myc is required to activate the Ataxia telangiectasia mutated (ATM)-dependent DNA damage checkpoint responses in rat cell lines exposed to ionizing radiation (IR) or the bacterial cytolethal distending toxin (CDT). Phosphorylation of the ATM kinase and its downstream effectors, such as histone H2AX, were impaired in the myc null cell line HO15.19, compared to the myc positive TGR-1 and HOmyc3 cells. Nuclear foci formation of the Nijmegen Breakage Syndrome (Nbs) 1 protein, essential for efficient ATM activation, was also reduced in absence of myc. Knock down of the endogenous levels of MYC by siRNA in the human cell line HCT116 resulted in decreased ATM and CHK2 phosphorylation in response to irradiation. Conversely, cell death induced by UV irradiation, known to activate the ATR-dependent checkpoint, was similar in all the cell lines, independently of the myc status.CONCLUSION: These data demonstrate that MYC contributes to the activation of the ATM-dependent checkpoint responses, leading to cell death in response to specific genotoxic stimuli.
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| 20. |
- Helander, Mikaela, et al.
(författare)
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Fractionation of Technical Lignin: Molecular Mass and pH Effects
- 2013
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Ingår i: BioResources. - : BioResources. - 1930-2126 .- 1930-2126. ; 8:2, s. 2270-2282
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Tidskriftsartikel (refereegranskat)abstract
- Today, lignin from kraft pulping is used mainly as fuel, with only very small amounts being used as raw material for chemicals and materials. This work focuses on using a convenient method for separating large amounts of low molecular weight lignin from the kraft process. Low molecular weight lignin contains larger amounts of phenolic structural units, which are possible modification sites and can be used as antioxidants. Moreover, a product that has reduced polydispersity, low molecular weight, and purified lignin could be a potential material for new applications. The studied process for separating lignin from weak black liquor used a membrane with a cut-off of 1000 Da. During precipitation of the 1000 Da permeate, it is necessary to prevent formation of fairly large, rigid particles/agglomerates of lignin by keeping the temperature low. To improve the dead-end filtration, higher ionic strength is needed for the weak black liquor. Additionally, reducing the end pH will cause more material to precipitate. More sulfur was found in the low molecular weight lignin and at lower precipitation pH, indicating that most sulfur left in the lignin samples might be bound to low molecular weight lignin.
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| 21. |
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| 22. |
- Henriksson, Gunnar, 1965-, et al.
(författare)
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Lignin Utilization
- 2010
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Ingår i: Thermochemical conversion of biomass to liquid fuels and chemicals. - : RSC Publishing. - 9781849732260 ; , s. 222-262
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Bokkapitel (refereegranskat)abstract
- Lignin is one of the most abundant biopolymers on Earth, carrying out important biological roles in vascular plants. It has somewhat higher energy content than polysaccharides, but has a complex and heterogeneous structure including covalent bonds to polysaccharides. The partly random structure of lignin is explained by the fact that it is created by an uncatalyzed radical polymerization. Lignin is obtained as a by-product of various types of technical processes based on biomass, of which chemical pulping of wood is the most important. These technical lignins have structures that differ from native lignin. Sulphite pulping of wood generates a water soluble lignin derivate, which among other things, is used as a dispersing agent and dust binder. Kraft pulping generates a lignin that is insoluble at neutral pH, which today is mainly burned for heat generation in the chemical recovery system of the kraft pulp mill. Recently, efficient methods have been developed for the preparation of lignin from the process liquids, for use in energy generation or other applications. Conversion of technical lignin to liquid fuels for use in combustion engines is an interesting possibility that represents a technical challenge. This chapter reviews the structure and biopolymerisation of lignin, reactions of lignin during technical processes, and different applications of technical lignins.
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| 23. |
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| 24. |
- 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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| 25. |
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| 26. |
- Jedvert, Kerstin, 1984, et al.
(författare)
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Mild steam explosion: A way to activate wood for enzymatic treatment, chemical pulping and biorefinery processes
- 2012
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Ingår i: Nordic Pulp and Paper Research Journal. - 2000-0669 .- 0283-2631. ; 27:5, s. 828-835
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Tidskriftsartikel (refereegranskat)abstract
- Industrially chipped wood chips of Norway spruce (Picea abies) were subjected to mild steam explosion (115 - 160 degrees C) in a small-scale steam explosion reactor. This was followed by kraft cooking or extraction in alkali at 130 degrees C for two hours, or by an enzymatic treatment with a culture filtrate in order to investigate the efficiency of the process in opening wood structure. The results demonstrated that mild explosion has an effect on opening wood structure, shown by increased release of glucomannans during alkaline extraction and faster delignification in kraft cooks for steam-exploded samples. The effect was also shown by analysis of the released reducing sugars of enzymatic treated wood chips, which showed that the wood structure became accessible for enzymes even at very modest mild steam explosion conditions. This was not observed in untreated wood chips, used as reference. The enzyme activity increased with increased temperature during mild steam explosion, and the effect did not seem to be linear. The mechanical effect of steam explosion seems to be of great importance at lower temperatures, and both chemical and mechanical effects are important at higher steam explosion temperatures. Samples for enzymatic treatment were taken both from the edges of wood chips as well as from the middle part of the chips, and the effect of steam explosion was somewhat greater in samples from the middle parts.
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| 27. |
- Li, Jiebing, et al.
(författare)
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The methoxy group of beta-O-methyl glucuronic acid is central for the formation of hexenuronic acid during kraft pulping
- 2011
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Ingår i: O Papel. - 0031-1057. ; 72:1, s. 54-65
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Tidskriftsartikel (refereegranskat)abstract
- Hexenuronic acid is created from 4-O-methyl gluc-uronic acid – a side chain group in xylan, and one of the most important hemicelluloses in both hardwood and softwood - during alkaline conditions, such as kraft pulping. Especially in hardwood kraft pulp, hexenuronic acid corresponds to a large part of the kappa number, and the presence of this component in bleached pulp causes post yellowing. In this work it is shown that glucuronic acid that lacks a methoxy group on the 4-carbon does not form hexenuronic acid under alkaline condition to the same extent as 4-O-methylglucuronic acid. This opens up novel strategies for genetic modification of the hemicellulose structures in wood cultivated for kraft pulping.
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| 28. |
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| 29. |
- 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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| 30. |
- Oinonen, Petri, et al.
(författare)
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Enzyme catalyzed cross-linking of spruce galactoglucomannan improves its applicability in barrier films
- 2013
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 95:2, s. 690-696
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Tidskriftsartikel (refereegranskat)abstract
- Hemicelluloses are one of the main constituents of plant cell walls and thereby one of the most abundant biopolymers on earth. They can be obtained as by-products from different wood based processes, most importantly from the mechanical pulping. Hemicelluloses have interesting properties in e.g. barrier film applications. However, their relatively low molecular weight after isolation and co-extraction with lignin has limited their use. In this work, we present a novel technique for increasing the molecular weight of different wood hemicelluloses from mechanical pulping process waters as well as from pre-hydrolysis extracts. This is achieved by enzyme-catalyzed cross-linking of aromatic moieties bound to the hemicelluloses. The cross-linking treatment resulted in significantly improved mechanical properties in barrier films made with spruce galactoglucomannan. To our knowledge, this is the first time that wood hemicelluloses have been cross-linked by utilizing the bound aromatic moieties and creates new possibilities for utilizing this raw material source.
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| 31. |
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| 32. |
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| 33. |
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| 34. |
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| 35. |
- Salehi Movahed, Alireza, et al.
(författare)
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Effect of model lignin structures on the oxidation of unsaturated fatty acids
- 2010
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Ingår i: Polymers from Renewable Resources. - : SAGE Publications. - 2041-2479 .- 2045-1377. ; 1:2
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study is to better understand vegetable oils as raw materials in the application of wood protection in order to obtain improved durability of exterior wood materials in an environmentally friendly way. This was done by studying the effect of lignin model compounds on the auto-oxidation rate of methyl linoleate. The auto-oxidation process of methyl linoleate was measured by itself and in combination with 1 wt% phenolic and non-phenolic lignin model compounds at 70°C. The effect of lignin compounds on the methyl linoleate auto-oxidation process was monitored by 1H-NMR, size exclusion chromatography (SEC), and real-time infrared spectroscopy (RT-IR). It was observed that phenolic groups and radical conjugation are the main contributors to an antioxidant effect of lignin compounds on the oxidation rate of the methyl linoleate. Ferulic acid, which is phenolic and contains a carboxylic group, has the largest antioxidant effect on methyl linoleate. It was also found that the antioxidant effect existed, despite the low solubility of ferulic acid in methyl linoleate. This research demonstrates that it is possible to follow the auto-oxidation process in real time to uncover the effects of wood constituents on the fatty acid auto-oxidation process. Additionally, this knowledge that drying rate of oil can be tuned with the addition of lignin compounds can be used to predict drying times when this oil is applied to different species of wood.
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| 36. |
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| 37. |
- Salehi Movahed, Alireza, et al.
(författare)
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Effect of wood carbohydrates on the oxidation of unsaturated fatty acids
- 2013
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Ingår i: Progress in organic coatings. - : Elsevier BV. - 0300-9440 .- 1873-331X. ; 76:7/8, s. 1068-1074
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study is to better understand the oxidation mechanism of the fatty acids applied on wood surfaces. In the present study, model hemicellulose compounds were used to measure the effect of polysaccharides on auto-oxidation of methyl linoleate utilizing infrared spectroscopy (RT-IR). The auto-oxidation process of methyl linoleate was measured in combination with 1 wt% reducing and non-reducing hemicellulose model compounds (HMC) at 70 degrees C. The effect of HMC on the methyl linoleate auto-oxidation process was also compared with the effects of glycerol and glyceraldehyde, using same analytical method and reaction conditions. The IR-spectra of methyl linoleate with 1 wt% carbohydrates before and after oxidation were analyzed and peak intensity variations during oxidation in the region of 3010 cm(-1), 990 cm(-1), and 970 cm(-1) were calculated during oxidation process. It was observed that lactose and sucrose accelerated the radical reactions; however, glycerol has an anti-oxidative effect on the fatty acids oxidation. An interaction mechanism for these findings is proposed and discussed.
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| 38. |
- Salehi Muhaved, Alireza, et al.
(författare)
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Oxidation of methyl linoleate in the presence of lignin
- 2011
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Ingår i: Progress in organic coatings. - : Elsevier BV. - 0300-9440 .- 1873-331X. ; 72:3, s. 325-333
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Tidskriftsartikel (refereegranskat)abstract
- The overall aim of this study is to develop new wood modifications using vegetable oils to obtain improved durability of wood materials in an environmentally friendly way. Nuclear magnetic resonance (NMR) and Fourier-transform infrared (FT-IR) spectroscopies were used to study oxidation and possible chemical coupling reactions between polyunsaturated fatty acids and model lignin compounds in order to better understand the interactions between oxidatively drying systems such as vegetable oils or alkyds with the lignin part in wood. This was done by studying mixtures of different model lignin compounds and methyl linoleate. The oxidation process was analyzed at 70 °C both in methyl linoleate alone and in combination with 20 wt% of lignin model compounds. The effects of those compounds on the oil polymerization processes were monitored by NMR (both 13C and 1H experiments) and the domain specific reactivity and patterning were then combined with FT-IR data. No covalent bonds having formed between the oil and the model compounds were detected by combination of several 13C/1H 2D NMR methods. From the spectra, the oxidation degrees of model compounds were calculated, and for some lignin model compounds alcohols were oxidized to carbonyls during the process. Those results were in excellent agreement with FT-IR data and oxidation mechanisms were proposed. The combination of both analytical techniques was necessary to have a better understanding of these systems: NMR demonstrated the absence of chemical bond and quantified oxidation degree of model lignin molecules while FT-IR focused on oil oxidation.
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| 39. |
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| 40. |
- Shaposhnikov, Sergey, et al.
(författare)
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Twelve-gel slide format optimised for comet assay and fluorescent in situ hybridisation
- 2010
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Ingår i: Toxicology Letters. - : Elsevier BV. - 0378-4274 .- 1879-3169. ; 195:1, s. 31-34
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Tidskriftsartikel (refereegranskat)abstract
- The comet assay is widely used to measure DNA damage and repair in basic research, genotoxicity testing and human biomonitoring. The conventional format has 1 or 2 gels on a microscope slide, 1 sample per slide. To increase throughput, we have designed and tested a system with 12 smaller gels on one slide, allowing incubation of individual gels with different reagents or enzymes. Thus several times more samples can be analysed with one electrophoresis run, and fewer cells and smaller volumes of test solutions are required. Applications of the modified method include treatment with genotoxic agents at different concentrations; simultaneous analysis of different lesions using a range of enzymes; analysis of cell extracts for DNA repair activity; and fluorescent in situ hybridisation (FISH) to comet DNA with specific labelled probes.
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| 41. |
- Stenström, Petter, et al.
(författare)
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Enlarging the undersized spillway of Höljes dam
- 2011
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Konferensbidrag (refereegranskat)abstract
- Höljes dam is one of the largest embankment dams in Sweden. Studies have shown that it suffers from several deficiencies that would jeopardize the safety of the dam during extreme floods. The major deficiencies include insufficient spillway discharge capacity in relation to the updated design flood and potential risk of erosion in the dam toe in case of large spillway discharges. To safely pass the higher design flood, four major rehabilitation options are evaluated with the help of hydraulic model tests. Option 1 refers to the use of the existing spillway in combination with extra water storage above the full reservoir retention level (FRRL). Option 2 includes construction of a new, separate tunnel spillway. In Option 3, a new gated spillway, 17 m in width, is added to the right of the existing one. Option 4 refers to construction of a new spillway in the form of a 155 m long overflow weir in the reservoir in combination with moderate storage above the FRRL. In Option 1 and 2, the width of the existing spillway channel remains the same and the stilling basin is enlarged, while in Option 3 and 4, the spillway channel is widened and the stilling basin volume is also increased. This paper addresses the advantages and disadvantages of those options. Together with other investigations, hydraulic model testing provides necessary basis for finalization of each design option in terms of spillway discharge capacity and waterway configuration. After weighing the pros and cons, the dam owner has chosen Option 3 as the final rehabilitation alternative. Further investigations are made to optimize the design.
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| 42. |
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| 43. |
- Tavast, Daniel, et al.
(författare)
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Selectiveness and efficiency of combined peracetic acid and chlorine dioxide bleaching stage for kraft pulp in removing hexeuronic acid
- 2011
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Ingår i: Cellulose Chemistry and Technology. - 0576-9787. ; 45:1-2, s. 89-95
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Tidskriftsartikel (refereegranskat)abstract
- Combined peracetic acid and chlorine dioxide bleaching stages of unbleached and oxygen delignified hardwood and softwood kraft pulps were compared with conventional chlorine dioxide and peracetic acid stages as to kappa number and viscosity reduction, selectivity and reduction of hexenuronic acid content. The combined stages were more efficient in kappa number reduction than those with only chlorine dioxide. Part of the increased kappa number reduction was due to an improved degradation of hexenuronic acid. The stages where chlorine dioxide was added before the peracetic acid (DT) showed a higher selectivity than those in which the chemicals were added simultaneously (D+T); in turn, the latter were more efficient than the "pure" chlorine dioxide (D, D-0) and peracetic acid stages (T). However, peracetic acid and chlorine dioxide seemed to react with each other, leading to the degradation of both bleaching chemicals. The mechanisms and practical implementation of these bleaching sequences are discussed.
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| 44. |
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| 45. |
- Wang, Yan, et al.
(författare)
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Increased Degradability of Cellulose by Dissolution in Cold Alkali
- 2014
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Ingår i: BioResources. - : BioResources. - 1930-2126. ; 9:4, s. 7566-7578
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Tidskriftsartikel (refereegranskat)abstract
- To enhance the degradability of cellulosic materials for further industrial purposes, different qualities of cellulose were dissolved in cold sodium hydroxide solution and precipitated by lowering the pH with sulfuric acid. The precipitated cellulose was subjected to acidic and enzymatic hydrolysis. The results showed that the precipitated cellulose degraded considerably faster both with enzymes and acid relative to the untreated controls. Important pretreatment parameters that can influence the degradability of the pretreated cellulosic materials were found to include temperature and concentration of the cellulose in NaOH solution. Increasing amounts of cellulose were hydrolysed with decreasing pretreatment temperature; the degradability of the pretreated cellulose increased with decreasing cellulose concentration. The degree of polymerization (DP) also can influence the pretreatment efficiency. Diluted sulfuric acid was able to decrease the DP and enhance the effect of dissolution and precipitation. The results showed that the lower DP of cellulosic materials caused an increase of degradability for the NaOH pretreated samples compared to untreated samples. The NaOH pretreatment was more effective for shorter chain cellulose.
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| 46. |
- Wang, Yan, et al.
(författare)
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Mild alkaline treatment activates spruce wood for enzymatic processing : A possible stage in bio-refinery processes
- 2011
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Ingår i: BioResources. - 1930-2126. ; 6:3, s. 2425-2434
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Tidskriftsartikel (refereegranskat)abstract
- The structure of wood is so compact that enzymes are too large to penetrate into the structure and thereby attack the wood components for modifications that can be valuable for various purposes. Here we present a pretreatment method based on traditional kraft pulping, which opens the wood structure, so that enzymes are able to attack the wood components. To study this kind of chemical pretreatment, spruce wood samples were treated at similar conditions used in kraft cooking at varying intensities (H-factors). To verify if the structure was "opened" for enzymes, the pretreated wood samples were incubated with a cellulolytic culture filtrate, and the released reducing sugar concentration after the enzymatic hydrolysis was measured. The results indicated that un-pretreated wood fibers could not be attacked by the enzymes, but already relatively mild pretreatment was sufficient for letting the culture filtrate attack wood polysaccharides, and more intensive treatments opened the structure further. The mildest treatments did not cause any significant yield losses of lignin (Klason lignin). Some galactoglucomannans were however lost during the pretreatments. The mechanisms behind the effect and the technical significance of the method are discussed.
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| 47. |
- 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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| 48. |
- Westerberg, Niklas, 1981, et al.
(författare)
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Separation Of Galactoglucomannans, Lignin, And Lignin-Carbohydrate Complexes From Hot-Water-Extracted Norway Spruce By Cross-Flow Filtration And Adsorption Chromatography
- 2012
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Ingår i: BioResources. - : BioResources. - 1930-2126. ; 7:4, s. 4501-4516
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Tidskriftsartikel (refereegranskat)abstract
- A simple method to simultaneously recover polymeric carbohydrates, mainly galactoglucomannans (GGM), lignin, and lignin-carbohydrate complex (LCC) from hot-water-extracted Norway spruce wood is presented. The isolation method consists of cross-flow filtration, where high and low molecular mass species are removed, followed by fixed-bed adsorption on a hydrophobic polymeric resin (XAD-16) to remove lignins and lignans. In the second step of fixed-bed adsorption, a phenylic reversed-phase analytical chromatography column, where mass transport resistance is minimized and a very high selectivity towards aromatic compounds have been observed, was used to separate LCC from GGM. The isolated LCC fraction contained about 10% aromatics, whereas the upgraded GGM fraction contained about 1.5% aromatics and the lignin fraction contained about 56% aromatics. Polymeric xylan was accumulated in the GGM fraction, while mannose was the dominant sugar found in the LCC fraction. As products, approximately 7% was recovered in the lignin fraction in the first adsorptive step, 5% was recovered as LCC, and 88% as upgraded hemicelluloses.
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| 49. |
- Zhu, Hongli, et al.
(författare)
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A novel nano cellulose preparation method and size fraction by cross flow ultra- filtration
- 2012
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Ingår i: Current organic chemistry. - : Bentham Science Publishers Ltd.. - 1385-2728 .- 1875-5348. ; :16, s. 1871-1875
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Tidskriftsartikel (refereegranskat)abstract
- A novel energy-efficient method called nanopulping (patent pending) to produce nanocellulose from chemical pulp, and a novel cross-flow ultra-filtration method to separate nanofibrils fractions of different size were applied in this study. Pretreatment with endoglucanase or 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidation seems to enhance the nanopulping process. Results were evaluated with atomic force microscope and ultrafiltration. The nanopulping produced a relatively inhomogeneous material with larger particles/ fibers in addition to nanofibers. However, by ultrafiltration of the material it was possible to obtain more homogeneous material in different dimensions with methods industrially acceptable.
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| 50. |
- Zhu, Hongli, et al.
(författare)
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A preliminary investigation on enzymatic oxidative polymerization of lignin
- 2011
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Ingår i: 16th International Symposium on Wood, Fiber and Pulping Chemistry. ; , s. 238-241
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Konferensbidrag (refereegranskat)abstract
- Enzyme catalyzed oxidative polymerization of technical bagasse lignin and low-molecular-weight ultra-filtered kraft pulp lignin (UFL) were studied in methanol-water solution. Lignin was dissolved in methanol-water solution at pH 13 in steam heated autoclave at 130°C for 2h. The polymerization reaction was conducted at 40°C with a commercial laccase under oxygen saturation. The weight-average molecular weight (Mw) of original macromonomer and polymerized lignin were characterized with alkaline size exclusion Chromatograph (SEC) system. Enzyme treatment increased the molecular weight of both technical bagasse lignin and ultra-filtered lignin up to 20 times. The reaction time and the enzyme dosage were studied to obtain the maximal molecular weight.
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