| 1. |
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| 2. |
- Abdel Hady, Ahmed Wagih Abdallah, 1990, et al.
(författare)
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In situ microstructural evolution of spruce wood during soda pulping using synchrotron X-ray tomography
- 2022
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 1437-434X .- 0018-3830. ; 76:7, s. 611-621
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Tidskriftsartikel (refereegranskat)abstract
- A new laboratory reactor to perform in situ studies of structural changes in wood during soda pulping using synchrotron X-ray tomography is presented. The reactor is of recirculation type to provide stable reaction conditions and mimic the industrial situation. Experiments have been performed using this reactor in situ at a synchrotron microtomography beamline to provide sequences of 3D images from which measurement of wood cell wall thickness have been possible for the first time. The results showed that the cell wall thickness increased significantly in the early stage of pulping (<10 min), which is due to the transportation of cooking chemicals through the tracheids, resin channels and pits into the cell wall, which is swollen with the increased pH. Subsequently, the cell wall thickness reduces over the processing time up to 60 min with a high rate, which is inferred to be due to the dissolution and transport of lignin and hemicellulose from the secondary walls, allowing for better transportation of active chemicals deep through the cell wall layers. After 60 min processing, the cell wall thickness reduction rate reduced, as dissolution of lignin and hemicelluloses from the cell walls ceased, while the remaining dissolution occurs mainly at the middle lamella.
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| 3. |
- Abdel Hady, Ahmed Wagih Abdallah, 1990, et al.
(författare)
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Micro/nano-structural evolution in spruce wood during soda pulping
- 2021
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 1437-434X .- 0018-3830. ; 75:8, s. 754-764
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Tidskriftsartikel (refereegranskat)abstract
- Alkaline delignification of wood tissue is the core of the global pulping technology and the most prominent large-scale separation of the main wood components. This work aims at improved understanding of the interplay between the topochemistry of alkaline pulping and the associated morphological changes. Morphology and chemical structure of partially soda-delignified wood chips were studied combining X-ray tomography (XRT), X-ray diffraction analysis and compositional characterization (lignin and carbohydrate content). The XRT studies of wet samples (providing 3D structural information without interfering drying effects), allowed observation of the cell wall separation as an increasing amount of lignin was removed with the increasing pulping time. Comparison between the microstructure of the surface and the central parts of the treated chips showed a more delignified microstructure at the surface, which highlights the dependence of the delignification process on the mass transport (hydroxide ions and lignin fragments) through the wood tissue. The crystallite size of cellulose increased in the <200> crystal planes during the early stage of pulping while there was little effect on the <110> plane.
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| 4. |
- Ahlbom, Anders, 1993, et al.
(författare)
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On the hydrothermal depolymerisation of kraft lignin using glycerol as a capping agent
- 2023
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 1437-434X .- 0018-3830. ; 77:3, s. 159-169
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Tidskriftsartikel (refereegranskat)abstract
- Depolymerisation of kraft lignin under hydrothermal conditions was investigated at short residence times (1–12 min) with glycerol being used as a capping agent. The weight average molecular weight (M w) of the products decreased within the first minute of residence time, with the inter-unit ether linkages breaking accordingly. Furthermore, the M w of the product fractions decreased at increasing residence times, while the char yield increased. Short residence times thus appear to be beneficial for mitigating the formation of char. Also, addition of NaOH reduced the yield of char. Although the addition of glycerol caused a decrease in the M w of the products, it seemed to increase the yield of char and therefore might not be a suitable capping agent for kraft lignin depolymerisation.
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| 5. |
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| 6. |
- Ahlbom, Anders, 1993, et al.
(författare)
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Towards understanding kraft lignin depolymerisation under hydrothermal conditions
- 2021
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 1437-434X .- 0018-3830. ; 76:1, s. 37-48
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Tidskriftsartikel (refereegranskat)abstract
- Kraft lignin depolymerisation using hydrothermal liquefaction suffers from the formation of char, resulting in a decreased product yield as well as causing operational problems. While this may be mitigated by the addition of capping agents such as phenol and isopropanol, other reaction parameters, for example reaction time and temperature, are also important for the product yields. In this work, the effect of short reaction times on the hydrothermal liquefaction of kraft lignin in an alkaline water and isopropanol mixture was investigated at 1-12 min and 290 °C. The results show that there were swift initial reactions: the major ether bonds in the lignin were broken within the first minute of reaction, and the molecular weight of all product fractions was halved at the very least. Longer reaction times, however, do not cause as pronounced structural changes as the initial reaction, indicating that a recalcitrant carbon-carbon skeleton remained in the products. Nevertheless, the yields of both char and monomers increased slowly with increasing reaction time. The swift initial depolymerising reactions were therefore followed by slower repolymerisation as well as a slow formation of monomers and dimers, which calls for careful tuning of the reaction time.
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| 7. |
- Ahlbom, Anders, 1993, et al.
(författare)
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Using guaiacol as a capping agent in the hydrothermal depolymerisation of kraft lignin
- 2023
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Ingår i: Nordic Pulp and Paper Research Journal. - 2000-0669 .- 0283-2631. ; 38:4, s. 619-631
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Tidskriftsartikel (refereegranskat)abstract
- The depolymerisation of softwood kraft lignin was investigated, under hydrothermal conditions at 290 °C and 250 bar, with guaiacol in the reactor feed to evaluate its impact on the formation of char and on the molecular weights of the products. The effect of residence time was investigated in the time span 1-12 min. Lignin is depolymerised during the process and guaiacol is both formed and consumed during the reaction, with clearly noticeable changes as early as in the first minute of reaction. Although the addition of guaiacol in the reactor feed causes a reduction in the weight average molecular weight of the products, the yield of char increases. Longer residence times result in repolymerisation of the reaction products as well as a further increase in the yield of monoaromatic components and char.
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| 8. |
- Ahlbom, Anders, 1993, et al.
(författare)
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Using Isopropanol as a Capping Agent in the Hydrothermal Liquefaction of Kraft Lignin in Near-Critical Water
- 2021
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Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 14:4
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Tidskriftsartikel (refereegranskat)abstract
- In this study, Kraft lignin was depolymerised by hydrothermal liquefaction in near-critical water (290-335 degrees C, 250 bar) using Na2CO3 as an alkaline catalyst. Isopropanol was used as a co-solvent with the objective of investigating its capping effect and capability of reducing char formation. The resulting product, which was a mixture of an aqueous liquid, containing water-soluble organic compounds, and char, had a lower sulphur content than the Kraft lignin. Two-dimensional nuclear magnetic resonance studies of the organic precipitates of the aqueous phase and the char indicated that the major lignin bonds were broken. The high molar masses of the char and the water-soluble organics, nevertheless, indicate extensive repolymerisation of the organic constituents once they have been depolymerised from the lignin. With increasing temperature, the yield of char increased, although its molar mass decreased. The addition of isopropanol increased the yield of the water-soluble organic products and decreased the yield of the char as well as the molar masses of the products, which is indicative of a capping effect.
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| 9. |
- Arumughan, Vishnu, 1994, et al.
(författare)
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Anion-Specific Adsorption of Carboxymethyl Cellulose on Cellulose
- 2023
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 39:42, s. 15014-15021
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Tidskriftsartikel (refereegranskat)abstract
- Integration of fiber modification step with a modern pulp mill is a resource efficient way to produce functional fibers. Motivated by the need to integrate polymer adsorption with the current pulping system, anion-specific effects in carboxymethylcellulose (CMC) adsorption have been studied. The QCM-D adsorption experiments revealed that CMC adsorption to the cellulose model surface is prone to anion-specific effects. A correlation was observed between the adsorbed CMC and the degree of hydration of the co-ions present in the magnesium salts. The presence of a chaotropic co-ion such as nitrate increased the adsorption of CMC on cellulose compared to the presence of the kosmotropic sulfate co-ion. However, anion-specificity was not significant in the case of salts containing zinc cations. The hydration of anions determines the distribution of the ions at the interface. Chaotropic ions, such as nitrates, are likely to be distributed near the chaotropic cellulose surface, causing changes in the ordering of water molecules and resulting in greater entropy gain once released from the surface, thus increasing CMC adsorption.
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| 10. |
- Arumughan, Vishnu, 1994, et al.
(författare)
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Calcium Ion-Induced Structural Changes in Carboxymethylcellulose Solutions and Their Effects on Adsorption on Cellulose Surfaces
- 2022
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 23:1, s. 47-56
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of carboxymethylcellulose (CMC) on cellulose surfaces is one of the most studied examples of the adsorption of an anionic polyelectrolyte on a like-charged surface. It has been suggested that divalent ions can act as a bridge between CMC chains and the surface of cellulose and enhance the CMC adsorption: they can, however, also alter the structure of CMCs in the solution. In previous investigations, the influence of cations on solution properties has been largely overlooked. This study investigates the effect of Ca2+ ions on the properties of CMC solutions as well as the influence on cellulose nanofibers (CNFs), which was studied by dynamic light scattering and correlated with the adsorption of CMC on a cellulose surface probed using QCMD. The presence of Ca2+ facilitated the multichain association of CMC chains and increased the hydrodynamic diameter. This suggests that the adsorption of CMCs at high concentrations of CaCl2 is governed mainly by changes in solution properties rather than by changes in the cellulose surface. Furthermore, an entropy-driven mechanism has been suggested for the adsorption of CMC on cellulose. By comparing the adsorption of CMC from H2O and D2O, it was found that the release of water from the cellulose surface is driving the adsorption of CMC.
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| 11. |
- Arumughan, Vishnu, 1994, et al.
(författare)
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Fundamental aspects of the non-covalent modification of cellulose via polymer adsorption
- 2021
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Ingår i: Advances in Colloid and Interface Science. - : Elsevier BV. - 0001-8686. ; 298
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Forskningsöversikt (refereegranskat)abstract
- The increasing need for new material applications based on cellulose demands increased functional diversity and thus new functionalisation/modification approaches. The non-covalent modification of cellulose fibres via the adsorption of functional polymers has emerged as a promising route for tailoring the properties of material. This review focuses on fundamental aspects of polymer adsorption on cellulose surfaces, where the adsorption of polyelectrolytes and non-polyelectrolytes are treated separately. Adsorption studies on model surfaces as well as cellulose macro-fibres are reviewed. A correlation of the adsorption findings with the Scheutjens-Fleer polymer adsorption theory is provided, allowing the fundamentals behind the polymer adsorption phenomenon and its context in utilization of cellulose fibres to be understood.
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| 12. |
- Arumughan, Vishnu, 1994, et al.
(författare)
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Specific ion effects in the adsorption of carboxymethyl cellulose on cellulose: The influence of industrially relevant divalent cations
- 2021
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 1873-4359 .- 0927-7757. ; 626
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of carboxymethylcellulose (CMC) on cellulose surfaces is of relevance from both academic and industrial perspectives as it facilitates resource-efficient modification of cellulose fibres that allows them to carry negative charges. It is known that, compared to monovalent ions, Ca2+ ions are superior ions in facilitating CMC adsorption and the subsequent introduction of charge on cellulose fibres. However, the formation and deposition of calcium oxide involved in this process necessitates the search for alternative cations. Magnesium ions form one of the more promising candidates since they are already used in the pulping process to prevent cellulose degradation during peroxide bleaching. This work aims at elucidating the effects of the industrially relevant alkaline earth metal divalent cations Mg2+ and Ca2+ on the CMC adsorption process onto cellulose surfaces. Quartz Crystal Microbalance (QCM-D) technology was used to follow the adsorption in model systems in real time, whereas the adsorption of CMC on commercial fibres was studied using polyelectrolyte titrations, total organic carbon (TOC) analysis and conductometric titrations. This study shows that the presence of Ca2+ ions was more favourable for the adsorption of CMC to both types of cellulosic surfaces than Mg2+ ions. The distinction in the adsorption behaviour in the presence of Mg2+ and Ca2+ is suggested to be due to the differences in the polarizability of the ions. The findings are decisive in designing efficient industrial processes for the adsorption of polyelectrolytes to cellulose surfaces of similar charge.
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| 13. |
- de la Motte, Hanna, 1983, et al.
(författare)
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Molecular characterization of hydrolyzed cationized nanocrystalline cellulose, cotton cellulose and softwood kraft pulp using high resolution 1D and 2D NMR
- 2011
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617. ; 85:4, s. 738-746
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Tidskriftsartikel (refereegranskat)abstract
- Nanocrystalline cellulose, cotton linters and softwood kraft pulp were reacted with the cationic epoxide 2,3-epoxypropyltrimethyl ammonium chloride (EPTMAC) according to two different procedures, whereof one was a solvent and reagent minimizing spray technique. The samples were subjected to acid hydrolysis and characterized by solution-state nuclear magnetic resonance (NMR). The spectra were obtained using a 600 MHz cryoprobe NMR instrument. The use of ion exchange SPE-column chromatography enhanced the intensity of the peaks derived from the modified monosaccharide residues and opened for detailed NMR characterization at low degrees of substitution. In addition to a consistent 9 ppm change in the initial shifts of carbons adjacent to substituted hydroxyl groups, the NMR spectra proved that other neighboring atoms were affected by the substitution. Unlike nanocrystalline cellulose and cotton cellulose, the softwood kraft pulp cationized with the spray technique demonstrated a higher preference for 0-6 (83%), on the expense of O-2 substitution (16%).
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| 14. |
- Eriksson, M., et al.
(författare)
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Time-resolved electrophoretic analysis of mobility shifts for dissociating DNA ligands
- 2005
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Ingår i: Electrophoresis. - : Wiley. - 0173-0835 .- 1522-2683. ; 26:3, s. 524-532
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Tidskriftsartikel (refereegranskat)abstract
- Intercalative binding of ligands to DNA can be demonstrated by helix unwinding, monitored by gel electrophoresis of supercoiled DNA, as electrophoretic mobility is sensitive to the topological DNA state. However, we show that an apparent lack of unwinding in an electrophoretic assay could be due to dissociation of the (intercalated) ligand during the analysis, rather than evidence for a nonintercalative mode of binding to DNA. Repetitive scanning during the electrophoresis ensures that release of the ligand during electrophoresis does not affect the measured degree of unwinding, based on the electrophoretic velocity being determined as a function of time. We use this assay to establish intercalation as a mode of binding to DNA for the cyanine dyes YO, YO-PRO as well as two enantiomeric forms of the ruthenium complexes [(phen)2 Ru(tatpp)Ru(phen)2]4+, and to support groove-binding for the new unsymmetrical cyanine dyes BOXTO and BOXTO-PRO. Groove-binding could be concluded from a lack of unwinding, because we could rule out that it is caused by release of the dye during the electrophoresis. The gel electrophoresis has the advantage over hydrodynamic techniques that much smaller sample amounts are required, and our time-resolved approach can be employed in all mobility-shift assays when applied to dissociating complexes.
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| 15. |
- Gunnarsson, Maria, 1987, et al.
(författare)
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Influence of urea on methyl β -D-glucopyranoside in alkali at different temperatures
- 2019
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 26:18, s. 9413-9422
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Tidskriftsartikel (refereegranskat)abstract
- The dissolution efficiency plays an important role on the properties of regenerated cellulose-based products. Urea is known to be one of the additives aiding to improve cellulose dissolution in the NaOH(aq) system. The acting mechanism caused by urea has been debated and one of the hypothesis is that urea could induce a conformational change on cellulose, which promotes dissolution. Here we used NMR spectroscopy on a model system for cellulose, namely, methyl β -D-glucopyranoside (β -MeO-Glcp) and compared chemical shifts and J couplings, which both are indicators for conformational changes, as a function of temperature and upon the addition of urea. We found that in NaOH(aq), the hydroxymethyl group changes its conformation in favour of the population of the gt rotamer, while the presence of urea induced temperature dependent conformational changes. Heteronuclear Overhauser effect experiments showed that urea associates with cellulose but in a non-specific manner. This suggests that urea rather than binding to the carbohydrate, changes the chemical environment inducing a change in conformation of β -MeO-Glcp and likely also for cellulose when dissolved in NaOH(aq) with urea.
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| 16. |
- Gunnarsson, Maria, 1987, et al.
(författare)
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On the interference of urea with CO 2 /CO 3 2- chemistry of cellulose model solutions in NaOH(aq)
- 2021
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617. ; 251
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Tidskriftsartikel (refereegranskat)abstract
- The CO2/CO32− chemistry of the cellulose/NaOH(aq) solutions has been recently reported to comprise a CO2 incorporation through formation of a transient cellulose carbonate intermediate along with cellulose – CO32− interactions. This work explores on molecular interactions arising when this chemistry is brought together with urea, the most common stabiliser of these solutions. 1H, 13C and steady-state heteronuclear Overhauser effect NMR studies on the cellulose analogues (methyl-β-glucopyranoside (β-MeO-Glcp) and microcrystalline cellulose), combined with pH and ATR-FTIR measurements, reveal concurrent interactions of urea with both CO2 and CO32−– leading to increased uptake of CO2 and a buffering effect. Yet, regardless of the presence of urea, the route of conversion from CO2 to CO32-, whether going through reaction with the carbohydrate alkoxides or OH−, is likely to determine the chemical environment of the formed CO32-. These findings shed a new light on rather overlooked, albeit prominent, interactions in these solutions with the readily absorbed air CO2, essential for further development and implementation, whether towards regenerated and modified cellulose or CO2-capturing concepts.
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| 17. |
- Gunnarsson, Maria, 1987, et al.
(författare)
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The CO 2 /CO 3 2− chemistry of the NaOH(aq) model system applicable to cellulose solutions
- 2020
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 27:2, s. 621-628
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Tidskriftsartikel (refereegranskat)abstract
- Molecular interactions governing the recently reported CO2/CO32− chemistry of cellulose/NaOH(aq) solutions are investigated using a cellulose analogue methyl-β-D-glucopyranoside in NaOH(aq) solutions under conditions feasible with cellulose dissolution. 1H, 13C and steady-state heteronuclear Overhauser effect NMR spectroscopy complemented by pH measurements reveal carbohydrate–CO32− interactions as an important component of this chemistry. However, depending on in which order carbohydrate and CO32− are brought together in NaOH(aq) this interaction is different with different implications on stability of the CO32− in the solution.
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| 18. |
- Gunnarsson, Maria, 1987, et al.
(författare)
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The CO2 capturing ability of cellulose dissolved in NaOH(aq) at low temperature
- 2018
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Ingår i: Green Chemistry. - 1463-9262 .- 1463-9270. ; 20:14, s. 3279-3286
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Tidskriftsartikel (refereegranskat)abstract
- Herein, we explore the intrinsic ability of cellulose dissolved in NaOH(aq) to reversibly capture CO2. The stability of cellulose solutions differed significantly when adding CO2 prior to or after the dissolution of cellulose. ATR-IR spectroscopy on cellulose regenerated from the solutions, using ethanol, revealed the formation of a new carbonate species likely to be cellulose carbonate. To elucidate the interaction of cellulose with CO2 at the molecular level, a C-13 NMR spectrum was recorded on methyl -d-glucopyranoside (MeO-Glcp), a model compound, dissolved in NaOH(aq), which showed a difference in chemical shift when CO2 was added prior to or after the dissolution of MeO-Glcp, without a change in pH. The uptake of CO2 was found to be more than twice as high when CO2 was added to a solution after the dissolution of MeO-Glcp. Altogether, a mechanism for the observed CO2 capture is proposed, involving the formation of an intermediate cellulose carbonate upon the reaction of a cellulose alkoxide with CO2. The intermediate was observed as a captured carbonate structure only in regenerated samples, while its corresponding NMR peak in solution was absent. The reason for this is plausibly a rather fast hydrolysis of the carbonate intermediate by water, leading to the formation of CO32-, and thus increased capture of CO2. The potential of using carbohydrates as CO2 capturing agents in NaOH(aq) is shown to be simple and resource-effective in terms of the capture and regeneration of CO2.
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| 19. |
- Gunnarsson, Maria, 1987, et al.
(författare)
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The potential of magnetisation transfer NMR to monitor the dissolution process of cellulose in cold alkali
- 2019
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 26:18, s. 9403-9412
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Tidskriftsartikel (refereegranskat)abstract
- Cellulose is the most important biopolymer on earth and, when derived from e.g. wood, a promising alternative to for example cotton, which exhibits a large environmental burden. The replacement depends, however, on an efficient dissolution process of cellulose. Cold aqueous alkali systems are attractive but these solvents have peculiarities, which might be overcome by understanding the acting mechanisms. Proposed dissolution mechanisms are for example the breakage of hydrophobic interactions and partly deprotonation of the cellulose hydroxyl groups. Here, we performed a mechanistic study using equimolar aqueous solutions of LiOH, NaOH and KOH to elucidate the dissolution process of microcrystalline cellulose (MCC). The pH was the highest for KOH(aq) followed by NaOH(aq) and LiOH(aq). We used a combination of conventional and advanced solution-state NMR methods to monitor the dissolution process of MCC by solely increasing the temperature from − 10 to 5 °C. KOH(aq) dissolved roughly 25% of the maximum amount of MCC while NaOH(aq) and LiOH(aq) dissolved up to 70%. Water motions on nanoscale timescales present in non-frozen water, remained unaffected on the addition of MCC. Magnetisation transfer (MT) NMR experiments monitored the semi-rigid MCC as a function of temperature. Interestingly, although NaOH(aq) and LiOH(aq) were able to dissolve a similar amount at 5 °C, MT spectra revealed differences with increasing temperature, suggesting a difference in the swollen state of MCC in LiOH(aq) already at − 10 °C. Furthermore, MT NMR shows a great potential to study the water exchange dynamics with the swollen and semi-rigid MCC fraction in these systems, which might give valuable insights into the dissolution mechanism in cold alkali.
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| 20. |
- Hackenstrass, Klara, et al.
(författare)
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Structure, flexibility and hydration properties of lignin dimers studied with Molecular Dynamics simulations
- 2024
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Ingår i: Holzforschung. - 1437-434X .- 0018-3830. ; 78:2, s. 98-108
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Tidskriftsartikel (refereegranskat)abstract
- Lignin is an abundant polymer found in wood and grasses, but due to its heterogeneity and complex macromolecular structure it has been less utilized than cellulose. While the building blocks are known, the way they are linked is less understood. Here, Molecular Dynamics simulations were used to systematically characterize seven linkages found in native lignin. Their influence on lignin and water structure, and their interactions were analyzed. The study is limited to guaiacyl (G-G) dimers connected by the following common softwood linkages; 5-5 ', 4-O-5 ' , alpha-O-4 ', beta-1 ', beta-5 ', beta-O-4 ' and beta-beta '. The simulations show that the linkage has a significant effect on conformational preference and lignin-water interaction. Especially, the behavior of the beta-O-4 ' shows unique properties, both in terms of conformational freedom and interaction with water. Within the beta-O-4 ' dimer, pi-pi stacking between the aromatic rings is possible. The molecule has two distinct common conformations, one compressed and one extended. These preferences also lead to a different effect of beta-O-4 ' dimer on the surrounding water, where water is found close to the linkage itself but expelled from the aromatic rings to a larger extent than the other linkages. These findings are important for lignin solubility as well as its depolymerization mechanisms.
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| 21. |
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| 22. |
- Hasani, Merima, 1978, et al.
(författare)
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Cationization of Cellulose by Using N-Oxiranylmethyl-N-Methylmorpholinium Chloride and 2-Oxiranylpyridine as Etherification Agents
- 2009
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Ingår i: Journal of Applied Polymer Science. - : Wiley. - 1097-4628 .- 0021-8995. ; 114:3, s. 1449-1456
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Tidskriftsartikel (refereegranskat)abstract
- Cationization of cellulose under aqueous alkaline conditions was studied. Two new epoxy reagents, N-oxiranylmethyl-N-methylmorpolinitim chloride and 2-oxiranylpyridine, were used for preparation of cationic cellulose ethers. Using the first agent, cationic ethers were obtained in one step, whereas the latter one yielded a reactive intermediate used as a precursor for two different cationizations. Etherification with the commonly used 2,3-epoxypropyltrimethylammonium chloride was also performed and used as a reference reaction. By changing water content in the reaction mixture two groups cellulose ethers with different degrees of cationization were prepared. As expected, reducing the water content resulted in a higher degree of etherification and hence a more pronounced cationic character of the obtained ethers. Characterization by FTIR, elemental- and gravimetric analysis confirmed the formation of the desired ethers. Their ability to interact with water and adsorb the acid dye, methyl orange, was also studied, confirming further introduction of the cationic substituents and revealing different reactivities of the used epoxy reagents. From characterization, it could be concluded that N-oxiranylmethyl-N-methylmorpholinium chloride exhibits higher reactivity toward cellulose than both the reference compounds and 2-oxiranylpyridine. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 1449-1456, 2009
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| 23. |
- Hasani, Merima, 1978
(författare)
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Chemical modification of cellulose-new possibilities of some classical routes
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Owning to its unique structure, along with the inexhaustible renewability, cellulose has been a subject of scientific and commercial interest for over 150 years. However, given attractive structural properties, such as stiffness, hydrophilicity, stereoregularity, potential for chemical modifications and ability to form superstructures, utilization of this biopolymer is far below its potential. The prospect of improving it is closely connected with chemical modification possibilities. The research presented in this thesis explores these possibilities with the emphasis on reactive groups employed for substitution of cellulose backbone in different modification systems. Under homogeneous conditions, in the system dimethyl sulfoxide/tetrabutylammonium fluoride four new esterfication agents for in situ activation of carboxylic acids were successfully employed in preparation of cellulose esters.In heterogeneous aqueous systems, focus was on readily quantified cationizations of cellulose accomplished by oxirane mediated etherifications. Reactions of two new etherification agents, 2-oxiranylpyridine and N-oxiranylmethyl-N-methylmorpholinium chloride were explored. Etherification with the former provided cellulose with reactive pyridine moieties that could be utilized in further functionalizations, i.e. quaternizations of the pyridine nitrogen yielding cationic celluloses. Further, etherification with N-oxiranylmethyl-N-methylmorpholinium chloride introduced good leaving groups, N-methylmorpholine moieties, which could be employed in subsequent self-crosslinking reactions. Obtained crosslinked materials exhibited remarkably altered structure accessibility, highly defined by choice of crosslinking conditions. Oxirane mediated cationization was further applied on surface cationzation of cellulose nanocrystals. Reaction with N-oxiranylmethyltrimethylammonium chloride yielded sufficient surface cationization required to provide electrostatic colloidal stabilization of their aqueous suspensions. Interestingly, these suspensions exhibited thixotropic gelling along with the typical tendencies to self-order.Another cationization method applied on cellulose nanocrystals was studied, as well. It was based on intermediate esterification of cellulose nanocrystals with chloroacetylchloride in a non-aqueous system, followed by subsequent substitution with a tertiary amine. This procedure yielded highly cationized cellulose nanocrystals with varying extent of surface and bulk modification. In spite of overall high surface cationization the modified nanocrystals lacked colloidal stabilization in aqueous suspensions, which is likely an effect of strong interactions between introduced groups.
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| 24. |
- Hasani, Merima, 1978, et al.
(författare)
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Nano-cellulosic materials: The impact of water on their dissolution in DMAc/LiCl
- 2013
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617. ; 98:2, s. 1565-1572
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Tidskriftsartikel (refereegranskat)abstract
- The dissolution behaviour of disassociated cellulosic materials in N,N-dimethylacetamide/lithium chloride (DMAc/LiCl) was investigated. The parameters monitored were chromatographic elution profiles and recovered mass by means of gel permeation chromatography (GPC) with RI detection. In order to elucidate the impact of the disassembly on cellulosic fibres, comparative studies were performed with the non-disassociated cellulose counterparts. The importance of the presence of water was addressed by Karl Fischer titration and solvent exchange experiments. Morphological changes during the dissolution process were studied by scanning electron microscopy (SEM). Dissolution of fibrillated cellulosic materials is impeded compared to the non-fibrillated material. This is a consequence of the high-surface-area fibrils prone to retain high amounts of water. Dissolution behaviour of nano-crystalline cellulosic materials appeared to be source-dependent. Due to the absence of entangled networks, these materials retain only water bound at the surface of the nano-crystallites, indicative of both the exposed surface area and solubility. The small cellulose nano-particles extracted from dissolving pulp show lower solubility compared to the large NCC particles from cotton.
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| 25. |
- Hasani, Merima, 1978, et al.
(författare)
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New coupling reagents for homogeneous esterification of cellulose
- 2007
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 14:4, s. 347-356
-
Tidskriftsartikel (refereegranskat)abstract
- A group of known, but in cellulose chemistry new coupling reagents for homogeneous esterification has been investigated: 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methyl-morpholinium chloride, N-methyl-2-bromopyridinium iodide, N-methyl-2-chloropyridinium iodide, and N-methyl-2-bromopyridinium tosylate. In order to study their ability to activate carboxylic acids in esterifications of cellulose they have been employed in synthesis of cellulose adamantate esters. Their effectiveness has been estimated in terms of degree of substitution of resulting esters and compared to that obtained with the commonly used N,N'-carbonyldiimidazole.
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| 26. |
- Hasani, Merima, 1978, et al.
(författare)
-
Self-crosslinking of 2-hydroxypropyl-N-methylmorpholinium chloride cellulose fibres
- 2011
-
Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 18:3, s. 575-583
-
Tidskriftsartikel (refereegranskat)abstract
- Crosslinking of cellulose fibres was obtained by inducing a substitution reaction in a cationic cellulose ether (NMM-cellulose) prepared by action of N-oxiranylmethyl-N-methylmorpholinium chloride. During the reaction the N-methylmorpholine moiety of the cellulosic ether acts as a leaving group facilitating a covalent bond formation between the ether substituent and a hydroxyl or other nucleophilic group present in the cellulose chain. In order to provide additional evidence of the suggested crosslinking route and investigate its possibilities, different reaction conditions have been investigated and assessed in terms of the obtained fibre properties. The crosslinked fibres were characterized by means of elemental analysis and structure accessibility studies, including accessibility to water, anions and nitrogen gas. According to these investigations heating at 105 A degrees C induces a significant crosslinking. Pre-treatment with acetone restricts it mainly to formation of intra-fibre crosslinks, whereas heating from water suppresses the reactivity but results nevertheless in highly crosslinked structure with both intra- and inter-fibre crosslinks involved.
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| 27. |
- Henniges, U., et al.
(författare)
-
Electron Beam Irradiation of Cellulosic Materials-Opportunities and Limitations
- 2013
-
Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 6:5, s. 1584-1598
-
Tidskriftsartikel (refereegranskat)abstract
- The irradiation of pulp is of interest from different perspectives. Mainly it is required when a modification of cellulose is needed. Irradiation could bring many advantages, such as chemical savings and, therefore, cost savings and a reduction in environmental pollutants. In this account, pulp and dissociated celluloses were analyzed before and after irradiation by electron beaming. The focus of the analysis was the oxidation of hydroxyl groups to carbonyl and carboxyl groups in pulp and the degradation of cellulose causing a decrease in molar mass. For that purpose, the samples were labeled with a selective fluorescence marker and analyzed by gel permeation chromatography (GPC) coupled with multi-angle laser light scattering (MALLS), refractive index (RI), and fluorescence detectors. Degradation of the analyzed substrates was the predominant result of the irradiation; however, in the microcrystalline samples, oxidized cellulose functionalities were introduced along the cellulose chain, making this substrate suitable for further chemical modification.
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| 28. |
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| 29. |
- Jedvert, Kerstin, 1984, et al.
(författare)
-
Analyses of wood components in mild steam explosion liquors from spruce
- 2014
-
Ingår i: Nordic Pulp and Paper Research Journal. - 2000-0669 .- 0283-2631. ; 29:4, s. 557-566
-
Tidskriftsartikel (refereegranskat)abstract
- Steam explosion at mild conditions is an intriguing pre-treatment method for future biorefineries. Here, mild steam explosion liquors, i.e. the condensed steam generated from water-impregnated and NaBH4-impregnated spruce at various steam explosion conditions, are comprehensively characterized. The characterization includes several chromatographic techniques along with nuclear magnetic resonance (NMR), in order to determine relative abundances of solubilized lignin, carbohydrates, and acetate content. The findings show that the main components in the liquors originated from hemicelluloses and, to some extent, wood extractives. Arabinose side substituents of arabinoglucuronoxylan were cleaved early during the steam treatment. The amount of (galacto) glucomannan in the liquors increased from 16% for the sample from the 4 bar (0.4 MPa) treatment, to 23% for the sample from the 7 bar treatment. The effects of different conditions on wood during NaBH4-treatment were also investigated. For this treatment, it was found that the degree of deacetylation increased at harsher conditions.
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| 30. |
- Karna, Nabin Kumar, et al.
(författare)
-
Unraveling the thermodynamics of the CO2 driven precipitation of cellulose in aqueous NaOH
- 2023
-
Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104 .- 1873-4421. ; 575
-
Tidskriftsartikel (refereegranskat)abstract
- Hypothesis: The incorporation of carbon dioxide into a sodium hydroxide solution containing cellulose may induce the formation of a transient cellulose carbonate intermediate, which readily hydrolyzes to carbonate ion, and this process is responsible for the instantaneous formation of loose cellulose aggregates. Simulations: We employed molecular dynamics simulations to gain insight into the role of carbon dioxide and related ions in the cellulose aggregation process. By performing free energy calculations using OPLS/AA force fields between cellulose chains at different ionic environments, we were able to gain additional information regarding the behavior and thermodynamics of the involved species and propose a potential mechanism for the aggregation of cellulose in these systems. Findings: Our hypothesis of the formation of an intermediate cellulose carbonate in the solution, which strongly favors carbon dioxide absorption and carbonate ion formation, is supported by the simulation results. These results suggest that the aggregation process is driven by entropy upon the introduction of carbonate ions into the system.
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| 31. |
- Kolavali, Reddysuresh, 1983, et al.
(författare)
-
The sorption of monovalent cations onto norway spruce: Model studies using wood flour and LiCl solution
- 2017
-
Ingår i: Journal of Wood Chemistry and Technology. - : Informa UK Limited. - 1532-2319 .- 0277-3813. ; 37:2, s. 110-123
-
Tidskriftsartikel (refereegranskat)abstract
- The transport of chemicals in a porous material such as wood is very complex and involves several processes: the diffusion of chemicals in the cell pores (lumen and pit pores), through the cell walls at certain conditions, and sorption of wood tissue. In the present study, batch sorption experiments were performed to examine the sorption of Li+ ions from an aqueous LiCl solution onto Norway spruce wood flour samples. The experimental methodology employed is suitable for differentiating the amount of ions sorbed onto the wood tissue and dissolved in the solution in wood pores. The apparent equilibrium sorption data were analyzed using two widely applied isotherm models: Langmuir and Freundlich. The results suggest that the sorption was spontaneous, and for the experimental conditions studied, probably involved several interaction types between the different functional groups of the wood and the Li+/Cl− ions.
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| 32. |
- Kolavali, Reddysuresh, 1983, et al.
(författare)
-
The sorption of monovalent cations onto wood flour and holocelluloses of Norway spruce: molecular interactions during LiCl impregnation
- 2017
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 1437-434X .- 0018-3830. ; 71:5, s. 373-381
-
Tidskriftsartikel (refereegranskat)abstract
- Active functional groups and interactions involved in the sorption of Li+ ions from an aqueous LiCl solution onto the Norway spruce sapwood (sW) flour have been investigated. To this purpose, sW was delignified by peracetic acid (PAA) treatments and the resulting holocelluloses (HC6 h, HC24 h, HC51 h, HC72 h, where the lower case data indicate the PAA treatment time) with various lignin contents were immersed in aqueous solution of LiCl and the sorption effects were studied by flame atomic emission spectroscopy (FAES), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS). The Brunauer- Emmett-Teller (BET) specific surface area increased from 1.5±0.0 m2g−1 to 2.4±0.1 m2g−1 for HC6 h, and from 1.6±0.03 m2g−1 to 2.7±0.6 m2g−1 for HC72 h upon LiCl treatment. It was found that Li+/Cl− retention occurs predominantly via O-containing functionalities and the carbohydrate-rich samples sorbed more Li+. Upon LiCl treatment, the mobility and accessibility of the wood matrix was enhanced, possibly by interference of the introduced ions with the existing intermolecular bonds.
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| 33. |
- Kozlowski, Aleksandra Maria, 1990, et al.
(författare)
-
Cellulose interactions with CO 2 in NaOH(aq): The (un)expected coagulation creates potential in cellulose technology
- 2022
-
Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617. ; 294
-
Tidskriftsartikel (refereegranskat)abstract
- Upon the search for a suitable processing method for cellulose, the dissolution in NaOH(aq) presents a real green potential, including its ability to sorb environmental CO2(g) affecting dissolution. Here, CO2(g) was delivered in a controlled way to the cellulose/NaOH(aq) system during the in-situ analysis with FTIR, pH and temperature meters, resulting in efficient coagulation of cellulose. Surprisingly, the coagulation occurred with a minimal loss of alkalinity. This was considered an effect of a specific interaction between the dissolved polymer and gas, resulting in the introduction of carbonate species, highly influential in the coagulation process. The process repeated at 25 °C and 5 °C suggested a strong influence of temperature. The conversion routes of the CO2(g) coagulant were also related to the dissolved state of the polymer. The recovered cellulose appeared competitive with EtOH recovery in terms of structure. The presented finding put a perspective on the utilisation of both the coagulation process and final materials in cellulose technology.
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| 34. |
- Kozlowski, Aleksandra Maria, 1990, et al.
(författare)
-
The overlooked interaction between cellulose and CO2(g) in NaOH(aq) turned into the potential for cellulose technology and carbon dioxide capture
- 2022
-
Ingår i: EWLP 2022 proceedings.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In the world finally turned towards sustainable and environment-friendly solutions cellulose could play the first fiddle in almost any industrial sector. The only obstacle standing in the way to unlimited applications follows from the characteristic of cellulose itself, namely, the remarkable stability of the polymer. Due to low degradation temperature, the range of processing methods to access industrially attractive cellulose is limited to dissolution. Amongst many studied cellulose solvents, the aqueous NaOH, even if limited in terms of concentration and temperature, has a great perspective. The NaOH (aq) is cheap, vastly available and carry real green potential. Although the concentration/temperature limitations of NaOH (aq) have been continuously studied, the natural, well-established ability of NaOH (aq) to sorpt environmental CO2 (g) has been consequently omitted in cellulose research. The results of the initial analysis carried out in our group demonstrated the pitfalls of such a proceeding. It was shown that cellulose exhibit a strong affinity for alkali-dissolved CO2 that could lead to the formation of carbonate intermediates. In follow up to previous studies, here we took the control over the gas delivery and conclusively studied the effect of CO2 upon cellulose in NaOH (aq). Here, we present the results of our complex analytical approach based on in-situ studies of reaction between cellulose and CO2 (g), with perspective to carbonation, pH and temperature changes in the system. Furthermore, we introduce the potential of cellulose carbonation in the regeneration of polymer; subsequently, the carbonation process is discussed in terms of mechanism, reversibility and its effect on the cellulose crystal structure. Our findings are presented with the implication for cellulose processability in the context of cellulose derivatives and regenerated fibres production.
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| 35. |
- Kron, Linus, 1996, et al.
(författare)
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A comparative study of the cell wall level delignification behaviour of four Nordic hardwoods during kraft pulping
- 2024
-
Ingår i: Holzforschung. - 1437-434X .- 0018-3830. ; 78:8, s. 434-445
-
Tidskriftsartikel (refereegranskat)abstract
- Wood is a heterogeneous material with significant variation among species. This inherent complexity poses a challenge to the continuous expansion of our understanding of the kraft process; yet previous pulping research has mainly been limited to a few species. This study investigates variations among some less studied species and their cell wall level delignification behaviour during kraft pulping. Ground wood of birch, beech, aspen, and alder were pulped at near-constant composition and temperature conditions. Minor, yet significant, differences in the rates of their delignification were observed: aspen had a pronounced fast rate during the initial stage, whereas alder delignified more slowly relative to its high initial lignin content. The dissolution of xylan was substantially faster for birch. In contrast, no substantial differences were detected between the species in the molecular weight and structure of the dissolved wood components, suggesting that the different delignification behaviours stem from variations in the residual phase. The molecular weight distribution of dissolved lignin was uniform during the initial stage of pulping, which is indicative of rapid and extensive fragmentation. Subsequently, the weight increased continuously for the remainder of the process, suggesting that the mass transfer within the cell wall influenced the overall delignification kinetics.
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| 36. |
- Kron, Linus, 1996, et al.
(författare)
-
Kraft cooking of birch wood chips: Differences between the dissolved organic material in pore and bulk liquor
- 2023
-
Ingår i: Holzforschung. - 1437-434X .- 0018-3830. ; 77:8, s. 598-609
-
Tidskriftsartikel (refereegranskat)abstract
- The delignification of birch chips during kraft pulping was investigated, targeting both the impregnation and cooking steps. Wood chips were impregnated using white liquor, white liquor + NaCl, water or NaCl aqueous solution. Then, the chips were cooked in batch autoclaves applying the same constant composition cooking conditions for all samples. Pulp and two fractions of black liquor (bulk liquor and centrifuged liquor representing the liquor inside the wood chips and fibers) were collected after different pulping times and analyzed for lignin and carbohydrate content. The dissolved wood components were precipitated from selected samples and characterized with respect to composition, molecular weight distribution and structural motifs. Cooking chemicals in the impregnation liquors led to faster delignification and xylan removal during cooking. Higher contents of lignin and xylan were measured in the lumen than in the bulk. The concentration profiles also showed accumulation of dissolved material in the lumen over time, suggesting significant mass transport limitation from lumen to bulk. Further analysis revealed higher fragmentation/degradation of dissolved material with increasing pulping time and in the bulk when compared to the lumen liquor, as demonstrated by the lower molecular weights and the changes in chemical shifts in the NMR spectra.
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| 37. |
- Marion de Godoy, Carolina, 1993, et al.
(författare)
-
Kraft pulping of model wood chips: Local impact of process conditions on hardwood delignification and xylan retention
- 2024
-
Ingår i: Holzforschung. - 1437-434X .- 0018-3830. ; 78:8, s. 446-458
-
Tidskriftsartikel (refereegranskat)abstract
- Local evolution of delignification and xylan removal inside wood chips was investigated throughout the initial stages of kraft cooking. Model chips of birch sapwood were pulped at 145, 155 and 165 » °C, utilizing white liquors with hydroxide content ranging from 0.25 to 0.55 » mol/kg. The composition of different sections in each cooked sample was then determined. Xylan was isolated from selected samples and analyzed using size exclusion chromatography and HSQC NMR. Most changes in concentration and structure of residual xylan occurred early in the process (<45 » min). Furthermore, xylan samples isolated from the tissue of different cooked chips had similar average molecular weights, indicating that temperature and alkali content had little impact over the extent of reactions affecting residual xylan. In contrast, xylan dissolution was significantly dependent on pulping conditions, increasing with hydroxide concentration. The lignin profile inside the cooked chips also varied with alkali content and temperature, and it was shown to be more uniform when applying low cooking temperatures (145 » °C). Finally, increased delignification and xylan removal were detected close to the transverse surfaces of chips (likely due to the fast mass transport in vessels/lumen), implying that anatomical features of wood can have a significant impact on pulping.
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| 38. |
- Martinsson, Axel, 1992, et al.
(författare)
-
Hardwood kraft pulp fibre oxidation using acidic hydrogen peroxide
- 2021
-
Ingår i: Nordic Pulp and Paper Research Journal. - : Walter de Gruyter GmbH. - 2000-0669 .- 0283-2631. ; 36:1, s. 166-176
-
Tidskriftsartikel (refereegranskat)abstract
- Gaining insight into the oxidation of hardwood kraft fibres using hydrogen peroxide at mildly acidic conditions was the main aim of this study. The oxidized hardwood pulp had an increased number of carbonyl groups and, when formed into sheets, an enhanced durability in water was seen due to the formation of cross-links, known as hemiacetals. The carbonyl groups formed were found to be mainly ketones with the exception of the case with longer reaction times (60-90 minutes) at 85 °C, where aldehydes were detected. Through compositional analysis it was found that mainly xylan was oxidized, likely due to the higher amount of xylan close to the surface of the fibre wall. The influence of xylan on the oxidation process was investigated using cold caustic extraction (CCE) performed prior to oxidation. When the CCE pulp was oxidized, there was an increased rate of introduced carbonyl groups and degradation was more pronounced. This is likely due to the accessible surface area being increased, caused by the formation of pores when the lower molecular weight xylan was being extracted during CCE.
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| 39. |
- Martinsson, Axel, 1992, et al.
(författare)
-
Modification of softwood kraft pulp fibres using hydrogen peroxide at acidic conditions
- 2020
-
Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 27:12, s. 7191-7202
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of this work was to provide softwood kraft pulp fibres with new functionalities by the introduction of carbonyl groups. Carbonyl groups are known to affect properties such as wet strength through the formation of covalent bonds, i.e. hemiacetals. The method developed involves oxidation using hydrogen peroxide at mildly acidic conditions. It was found that the carbonyl group content increased with both increasing temperature and residence time when oxidized at acidic conditions. The number of carboxylic groups, however, remained approximately constant. There was virtually no increase in carbonyl groups when oxidation was performed at alkaline conditions. The maximum increase in carbonyl groups was found at a residence time of 90 min, a reaction temperature of 85 °C and a pH of 4. These conditions resulted in an increase in carbonyl groups from 30 to 122 µmol/g. When formed into a sheet, the pulp oxidized at acidic conditions proved to maintain its structural integrity at aqueous conditions. This indicates the formation of hemiacetal bonds between the introduced carbonyl groups and the hydroxyl groups on the carbohydrate chains. Thus, a possible application for the method could be fibre modification during the final bleaching stage of softwood kraft pulp, where the wet strength of the pulp could be increased.
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| 40. |
- Martinsson, Axel, 1992, et al.
(författare)
-
Physical properties of kraft pulp oxidized by hydrogen peroxide under mildly acidic conditions
- 2022
-
Ingår i: Nordic Pulp and Paper Research Journal. - : Walter de Gruyter GmbH. - 2000-0669 .- 0283-2631. ; 37:2, s. 330-337
-
Tidskriftsartikel (refereegranskat)abstract
- The objective of this study is to gain further insight into the compositional and physical changes of kraft pulp caused by oxidation with hydrogen peroxide under acidic conditions. A softwood kraft pulp has been subjected to varying degrees of oxidation. Changes in the composition, as well as resulting physical properties of laboratory sheets were investigated. Findings indicated that the oxidation resulted in an increased carbonyl group content, a decrease in intrinsic viscosity and a change in hemicellulose composition. The oxidized pulps were found to have a reduced water retention value and a slightly reduced tensile strength (4-11 % at the investigated conditions). However, a substantial increase in wet web tensile strength (6-23 %) and wet tensile strength (134-242 %) of the sheets was obtained. The sheets could easily be repulped and an increased wet strength maintained to a large extent, even after recycling of the sheets.
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| 41. |
- Martinsson, Axel, 1992, et al.
(författare)
-
The influence of transition metal ions on the oxidation of kraft pulp using hydrogen peroxide under mildly acidic conditions
- 2023
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 1437-434X .- 0018-3830. ; 77:5, s. 318-325
-
Tidskriftsartikel (refereegranskat)abstract
- Oxidation of kraft pulp using hydrogen peroxide under mild acidic conditions can be applied in order to obtain new functionality of the fibres, in the form of carbonyl groups. The hydrogen peroxide concentration must, however, be higher than consumed by the oxidation reactions meaning that the liquid must be recirculated to fully utilize the hydrogen peroxide. This paper investigates the consequences of recirculation of the oxidation liquor. It was found that recirculation results in an accumulation of ions of transition metals (copper, iron and manganese) in the oxidation liquor. The transition metal ions are known for catalytic decomposition of hydrogen peroxide, producing radicals which may react with carbohydrates, forming carbonyl groups as well as causing carbohydrate degradation. This was confirmed through the recirculation of oxidation liquor as well as through controlled addition of transition metals. At high transition metal ion concentration the reactions were fast and a severe degradation of carbohydrates was observed, accompanied by a rapid hydrogen peroxide consumption. The consequence of this, in an industrial context, is that the concentration of metal ions must be carefully controlled in order to add functionality to the cellulose without causing excessive degradation of carbohydrates or consumption of hydrogen peroxide.
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| 42. |
- Mattsson, Cecilia, 1970, et al.
(författare)
-
About structural changes of lignin during kraft cooking and the kinetics of delignification
- 2017
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 71:7-8, s. 545-553
-
Tidskriftsartikel (refereegranskat)abstract
- Wood meal was submitted to kraft cooking in a small-scale flow-through reactor and the structural changes of lignin have been investigated. The rate determining steps in kraft cooking were in focus. Based on two-dimensional nuclear magnetic resonance (2D-NMR) measurements on lignin fractions extracted at different cooking times from the black liquor, it was observed that the main lignin reactions occur within 10-20 min and thus the kinetics of the chemical reaction cannot be the rate-determining step. On the other hand, the molecular weight (MW) of lignin is shifted towards larger fragments in the course of cooking time but the MW decreases with increasing ionic strength. Obviously, the kinetics of the delignification are strongly dependent on solubility and/or mass transport at the cell wall level. At chip size level, the mass transport of cooking chemicals into the wood chip may influence the overall kinetics in the initial part of the cooking. At longer cooking times the concentration of chemicals becomes sufficiently high in the wood chips, and the delignification is progressively governed by solubility and/or mass transport of lignin molecules occurring at the cell wall level.
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| 43. |
- Naserifar, Shirin, 1991, et al.
(författare)
-
Aqueous N,N-dimethylmorpholinium hydroxide as a novel solvent for cellulose
- 2021
-
Ingår i: European Polymer Journal. - : Elsevier BV. - 0014-3057 .- 1873-1945. ; 161
-
Tidskriftsartikel (refereegranskat)abstract
- N,N-dimethylmorpholinium hydroxide was synthesized and its ability to dissolve microcrystalline cellulose and pulp was assessed for the first time. Microscopy and UV–Vis measurements showed that dissolution occurred over a range of 1–2 M concentration of the solvent and a maximum solubility of 7 wt% microcrystalline cellulose could be achieved. The stability of cellulose solutions was evaluated by size exclusion chromatography, which did not detect degradation to any noticeable extent. This observation was further confirmed by 13C NMR measurements. Finally, DLS studies confirmed that most of the cellulose was molecularly dissolved, with intrinsic viscosity values indicating cellulose chains expansion in this solvent.
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| 44. |
- Naserifar, Shirin, 1991, et al.
(författare)
-
Cellulose gelation in aqueous hydroxide solutions by CO 2 (g): Fact and theory
- 2024
-
Ingår i: Carbohydrate Polymer Technologies and Applications. - : Elsevier Ltd. - 2666-8939. ; 7
-
Tidskriftsartikel (refereegranskat)abstract
- Understanding how the solvent structure affects the stability of the dissolved state and the following precipitation is important for designing future dissolution-coagulation systems for cellulose processing. In this study, two morpholinium hydroxides with different alkyl chain lengths, namely N,N-dimethylmorpholinium hydroxide (NDMMOH(aq)) and N‑butyl‑N-methyl morpholinium hydroxide (BMMorOH(aq)), were studied and compared with the previously thoroughly investigated cellulose solvent benzyltriemethylammonium hydroxide (Triton B(aq)) which is well-known for its superior ability to stabilize the dissolved state. Cellulose solutions in each solvent were characterized by NMR, flow and frequency sweeps, while cellulose coagulation by CO2(g) was followed by in situ FTIR, pH and temperature measurements. The coagulated systems were characterized by CP/MAS 13C NMR, flow, and frequency sweep measurements. Complementary molecular dynamic (MD) simulations were performed to gain a deeper insight into the observed gelation behavior. The intrinsic viscosity indicated more extended cellulose chains in the solvents with more hydrophobic moieties (Triton B and BMMorOH). Even though the course of coagulation did not show any significant differences during monitoring, both the properties of the obtained gels and the MD simulations indicated differences in formation and properties of the coagulated materials that could be related both to the choice of solvent and coagulant.
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| 45. |
- Naserifar, Shirin, 1991, et al.
(författare)
-
In situ monitoring of cellulose etherification in solution: probing the impact of solvent composition on the synthesis of 3-allyloxy-2-hydroxypropyl-cellulose in aqueous hydroxide systems
- 2022
-
Ingår i: Polymer Chemistry. - : Royal Society of Chemistry (RSC). - 1759-9954 .- 1759-9962. ; 13:28, s. 4111-4123
-
Tidskriftsartikel (refereegranskat)abstract
- Etherification of cellulose using allyl glycidyl ether was carried out in aqueous alkaline solutions of benzyltrimethylammonium hydroxide, tetramethylammonium hydroxide, NaOH and different mixtures of these bases in order to study the effect of hydroxide base composition on the course of the reaction and the resulting product properties. In situ FTIR spectroscopy and time sweep shear measurements were carried out to monitor the reactions in real time. Infrared Attenuated Total Reflectance Spectroscopy and H-1 NMR confirmed the synthesis of 3-allyloxy-2-hydroxypropyl-cellulose and 2D HSQC NMR confirmed substitution on C2, C3 and C6 in all of the solvents. Quantitative C-13 NMR was used to estimate the molar substitution. Cellulose solutions in these quaternary ammonium hydroxides showed higher stability at 50 degrees C during the course of reaction, faster dissolution and hydrolysis of allyl glycidyl ether and lower molar substitution values compared to NaOH. Even though the highest molar substitution value was obtained in NaOH, the isolated product from this medium had lower solubility in DMSO-d(6) and its C-13 NMR did not differ significantly except for higher intensity of C1 and C6 compared to the other spectra. The obtained results indicated a more pronounced cascade reaction on the substitution itself in NaOH and lower temperature stability of cellulose solutions in this solvent.
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| 46. |
- Naserifar, Shirin, 1991, et al.
(författare)
-
Investigation of cellulose dissolution in morpholinium-based solvents: impact of solvent structural features on cellulose dissolution
- 2023
-
Ingår i: RSC Advances. - 2046-2069. ; 13:27, s. 18639-18650
-
Tidskriftsartikel (refereegranskat)abstract
- A series of N-methylmorpholinium salts with varying N-alkyl chains and Cl−, OAc− and OH− as counter ions have been synthesized and investigated for their ability to dissolve cellulose, aiming at elucidating solvent structural features affecting cellulose dissolution. Synthesis procedures have been developed to, to a high extent, rely on conversions in water and microwave-assisted reactions employing a reduced number of work-up steps and ion-exchange resins that can be regenerated. Water solutions of morpholinium hydroxides proved capable of dissolving cellulose, with those of them possessing alkyl chains longer than ethyl showing surprising dissolution ability at room-temperature. Morpholinium acetates behaved as ionic liquids, and were also capable of dissolving cellulose when combined with DMSO. The obtained cellulose solutions were characterized according to their chemical and colloidal stability using 13C NMR spectroscopy, size exclusion chromatography and flow sweep measurements, while the ethanol coagulates were investigated in terms of crystallinity using solid state NMR. In contrast, the morpholinium chlorides obtained were hygroscopic with high melting points and low solubility in common organic solvents e.g., acetone, DMSO and DMAc, thus lacking the ability to swell or dissolve cellulose.
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| 47. |
- Naserifar, Shirin, 1991, et al.
(författare)
-
Probing the Impact of the Hydroxide Base Composition on Ethrerification of Cellulose
- 2021
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Over the years, developing cellulose derivatives has been an active filed of research mainly due to the enhanced processability of these compounds. In this regard, cellulose ethers have been of high commercial importance with a wide spectrum of applications as thickeners, emulsifiers, binders and film formers. Generally, homogeneous or heterogeneous reaction conditions are applied to afford cellulose ethers. However, etherification under homogeneous conditions lead to equally available hydroxyl groups as well as more control over substitution distribution and thus enhanced product properties. Recently, in our group quaternary ammonium hydroxides (QAHs) as homogeneous dissolving systems and the role of the counter cation on cellulose dissolution have been investigated. In continuation of our previous work and to shed light upon the impact these QAHs solvents on modification of cellulose by varying the hydroxide composition in presence and absence of NaOH, we aimed at studying allyl cellulose synthesis as an important class of cellulose ethers possessing an active C=C double bond. In-situ IR spectroscopy and in-situ rheology measurements were used to monitor the reactions in real time. To the best of our knowledge, this is the first report on monitoring the cellulose etherification reaction using in-situ IR spectroscopy. Besides, additional characterisation methods including ATR-FTIR, 1D and 2DNMR have been used to confirm the product formation and assess its properties.
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| 48. |
- Palme, Anna, 1986, et al.
(författare)
-
Differences in swelling of chemical pulp fibers and cotton fibers-Effect of the supramolecular structure
- 2019
-
Ingår i: BioResources. - : North Carolina State University. - 1930-2126. ; 14:3, s. 5698-5715
-
Tidskriftsartikel (refereegranskat)abstract
- The swelling and dissolution of cellulose are key parameters in the production of regenerated cellulose fibers. Since cotton is almost pure cellulose, it has been proposed that the recycling of cotton textiles may be accomplished through incorporating the cotton textiles into the production of regenerated cellulosic fibers. In this study, the supramolecular structure before and after pretreatment was characterized using solid-state carbon-13 nuclear magnetic resonance (13C NMR), and the findings related to the swelling of dissolving pulp and cotton were quantified with a fiber analyzer. The cotton and dissolving pulp samples were subjected to three different pretreatments: mild acid hydrolysis, acid hydrolysis in ethanol, and a hydrothermal treatment. The results showed that cotton was harder to swell than the dissolving pulp. This indicated that either waste cotton requires another type of activating pretreatment than those included in this study or very good solvents if it is to be included in the production of regenerated fibers.
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| 49. |
- Sahlin, Karin, 1991, et al.
(författare)
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Nanocellulose in biocomposites
- 2016
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Ingår i: Proc Materials for Tomorrow 2016. ; , s. Nr 41-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 50. |
- Swensson, Beatrice, 1992, et al.
(författare)
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Probing interactions in combined hydroxide base solvents for improving dissolution of cellulose
- 2020
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Ingår i: Polymers. - 2073-4360. ; 12:6
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Tidskriftsartikel (refereegranskat)abstract
- To further understand cellulose-solvent interactions in aqueous hydroxide solutions, cellulose behavior in aqueous solutions of NaOH combined with tetramethylammonium hydroxide (TMAH) or benzyltrimethylammonium hydroxide (Triton B), as well as urea, was investigated. The rheological properties of the solutions were assessed throughflowsweeps at different temperatures, and the intermolecular interactions were probed using solvatochromic dyes. The results showed that NaOH combined with TMAH had synergistic effects on cellulose dissolution and was a better solvent for cellulose than the combination of NaOH with Triton B, in spite of the superior dissolution ability of Triton B alone. This somewhat unexpected finding shows that the base pair needs to be selected with care. Interestingly, addition of urea had no significant effect on the solvatochromic parameters or dissolution capacity of solutions of Triton B but rendered improved stability of solutions containing NaOH and/or TMAH. It seems that both urea and Triton B weaken the hydrophobic assembly effect of these solutions, but urea is excluded from interacting with cellulose in the presence of Triton B. This study provides further insight into dissolution of cellulose and the possibility of utilizing combinations of hydroxide bases to achieve improved solution properties.
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