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  • 1. Hafrén, J.
    et al.
    Westermark, Ulla
    Lennholm, U.
    Terashima, N.
    Formation of specifically C-13 enriched DHP in lignifying tissue1999Conference paper (Other academic)
  • 2. Hafrén, Johan
    et al.
    Westermark, Ulla
    Distribution of acidic and esterified polygalacturonans in sapwood of spruce, birch and aspen2001In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 16, no 4, p. 284-290Article in journal (Refereed)
    Abstract [en]

    The distribution and degree of esterification of polygalacturonans have been studied in spruce, birch and aspen using immunolocalization. Monoclonal antibodies against acidic and methyl esterified polygalacturonan were localized by fluorescence- and transmission electron microscopy.

  • 3.
    Hafrén, Jonas
    et al.
    Swedish Pulp and Paper Research Institute.
    Daniel, Geoffrey
    Sveriges Lantbruksuniversitet.
    Westermark, Ulla
    The distribution of acidic and esterified pectin in cambium, developing xylem and mature xylem of Pinus sylvestris2000In: IAWA Journal, ISSN 0928-1541, Vol. 21, no 2, p. 157-168Article in journal (Refereed)
    Abstract [en]

    Homogalacturonans with low and high degree of methyl esterification have been immuno-localised in the cambium, differentiating xylem and mature xylem of Pinus sylvestris, by monoclonal antibodies JIM5 and JIM7. In the unlignified cambial tissue the antibodies revealed a similar distribution for acidic and esterified pectin in the compound middle lamella, ray cell walls and pit membranes. In the lignified xylem tissue, pectin was also found in the compound middle lamella, although dominantly in the methylesterified form. Lignification seemed to coincide with a decrease in the presence of acidic pectin in the compound middle lamella. Both antibodies indicated labelling in pit membranes and ray cell walls in partially and fully lignified wood fibres.

  • 4.
    Hafrén, Jonas
    et al.
    Swedish Pulp and Paper Research Institute, Stockholm.
    Fujino, Takeshi
    Wood Research Institute, Kyoto University,.
    Itoh, Takao
    Wood Research Institute, Kyoto University,.
    Westermark, Ulla
    Terashima, Noritsugu
    Swedish Pulp and Paper Research Institute, Stockholm.
    Ultrastructural changes in the compound middle lamella of Pinus thunbergii during lignification and lignin removal2000In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 54, no 3, p. 234-240Article in journal (Refereed)
    Abstract [en]

    The structure of the middle lamella in Pinus thunbergii has been studied by the rapid-freeze deep-etching (RFDE) technique in combination with transmission electron microscopy (TEM). The ultrastructure of the compound middle lamella was studied in the early phases of the development of woody tissue in the cambial and differentiating xylem, before the heavy incrustation with lignin had occurred. Lignified middle lamella in the xylem was studied both directly and after delignification. It was found that the structure of the unlignified middle lamella in the cambium/developing xylem consists of a fine irregular network probably containing pectin and hemicellulose. As a result of lignin incrustation, the middle lamella becomes increasingly dense and the surface structure of the fully lignified middle lamella appeared to be compact and partly covered with globular structures. After delignification of the lignified middle lamella a thin network with a different structure was revealed. This network probably mainly consists of hemicellulose. No microfibrils of the type that occurs in the primary and secondary walls were found in the middle lamella.

  • 5.
    Hafrén, Jonas
    et al.
    STFI, Stockholm.
    Westermark, Ulla
    Lennholm, Helena
    Royal Institute of Technology.
    Terashima, Noritsugu
    STFI, Stockholm.
    Formation of 13C-enriched cell-wall DHP using isolated soft xylem from Picea abies2002In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 56, no 6, p. 585-591Article in journal (Refereed)
    Abstract [en]

    Cell-wall dehydrogenation polymers (CW-DHP) were prepared by incubating a mixture of soft xylem (differentiating xylem) from Picea abies, coniferin 13C-enriched at the side-chain β-carbon and unenriched coniferin, both with and without the addition of β-glucosidase and glucose oxidase, which causes an in situ polymerisation of the coniferyl alcohol in the cell wall. From difference solid state 13C-NMR spectra between 13C-enriched CW-DHP and unenriched CW-DHP, the bond frequencies involving specifically 13C-enriched carbon can be quantitatively determined. The sub-structures in CW-DHP prepared without the addition of β-glucosidase and glucose oxidase showed more similarity to protolignin than CW-DHP prepared with the addition of extraneous enzymes. The CW-DHP obtained without the addition of enzymes contained 36% β-O-4-derived sub-structures, 44% combined β-β, β-5 and β-1 sub-structures and 20% coniferyl alcohol/coniferaldehyd end groups. After acetone/water extraction of the CW-DHP, the content of β-β, β-5 and β-1 structures decreased by 4%, and the β-O-4 dominating peak increased by 4%. The 13C-enriched CW-DHP material can be used to study lignin reactions in a solid wood matrix, and is also a powerful system for detailed studies on in vivo lignification mechanisms and the effects on lignification conditions on lignin structure

  • 6.
    Karlsson, Olov
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Pettersson, B.
    Westermark, Ulla
    Linkages between residual lignin and carbohydrates in bisulphite (magnefite) pulps2001In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 27, no 9, p. 310-316Article in journal (Refereed)
    Abstract [en]

    The presence of bonds between residual lignin and carbohydrates in bisulphite pulps from hardwoods and softwoods was studied. Results showed that a fraction of the residual lignin was bonded to cellulose in bisulphite pulps of softwood. The treatment with xylanase indicated the existence of alkali-stable lignin-xylan bonds in softwood bisulphite pulps.

  • 7.
    Karlsson, Olov
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Pettersson, B.
    Westermark, Ulla
    The use of cellulases and hemicellulases to study lignin-cellulose as well as lignin-hemicellulose bonds in kraft pulps2001In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 27, no 6, p. 196-201Article in journal (Refereed)
    Abstract [en]

    The combination of carbohydrate-degrading enzymes and size-exclusion chromatography (SEC) has been used to analyze the existence of covalent bonds between lignin and cellulose and/or hemicelluloses in pulps. Cellulases and xylanase were used for degradation of cellulose and xylan, respectively. Analysis of the molecular weight profiles of lignin and carbohydrates before and after enzymic hydrolysis were performed by dissolution of the pulps in LiCl/dimethylacetamide (DMAC). The results indicate that a considerable part of the residual lignin in unbleached pine kraft pulp is bond to cellulose. Bonding of lignin to xylan in the pine kraft pulp could also be detected. Analysis of birch kraft pulp shows that most of the residu lignin in birch kraft pulps is covalently linked to xylan. The combination of carbohydrate-degrading enzymes and SEC in LiCl/DMAC seems to be an excellent way of characterizing bonds between lignin and carbohydrates in chemical pulps.

  • 8.
    Karlsson, Olov
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Westermark, Ulla
    Auto-adhesive bonding by oxidative treatment of wood2003In: Proceedings of the 12th International Symposium on Wood and Pulping Chemistry: University of Wisconsin-Madison, Department of Forest Ecology and Management, June 9 - 12, 2003, Madison, Wisconsin, USA, Madison, Wis, 2003, p. 365-368Conference paper (Refereed)
  • 9.
    Karlsson, Olov
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Westermark, Ulla
    Evidence for chemical bonds between lignin and cellulose in kraft pulps1996In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 22, no 10, p. J397-401Article in journal (Refereed)
    Abstract [en]

    The cellulose solvent system LiCl-dimethylacetamide has been used to dissolve kraft pulps prepared from pine and birch. The dissolved polymers were analyzed using size-exclusion chromatography combined with both RI- and UV-detection systems in order to monitor simultaneously the major wood polymers (cellulose, hemicellulose and lignin). Kraft pulps from birch were completely soluble in the solvent system and the pine kraft pulp about 80% soluble. Analyses of the kraft pulps strongly suggest that a considerable amount of the residual lignin is chemically linked to the high molecular weight cellulose in pine but not in birch. The presence of stable lignin-cellulose bonds will reduce the possibility of achieving a low kappa number by cooking. For comparison, sulphite and bisulphite pulps were also examined. Both pulps were soluble in the solvent system and analyses indicated that lignin-cellulose bonds also exist in these pulps although to a significantly lesser extent than in the pine kraft pulp

  • 10.
    Karlsson, Olov
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Westermark, Ulla
    Resin-free particleboard by oxidation of wood2002In: 6th Pacific Rim Bio-Based Composites Symposium & Workshop on the Chemical Modification of Cellulosics: November 10th to 13th 2002, Portland, Oregon ; proceedings / [ed] P. E. Humphrey, Corvallis, Or: Wood science and engineering department , 2002Conference paper (Refereed)
  • 11.
    Karlsson, Olov
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Westermark, Ulla
    The significance of glucomannan for the condensation of cellulose and lignin under kraft pulping conditions1997In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 12, no 2, p. 90-Article in journal (Refereed)
  • 12.
    Karlsson, Olov
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Westermark, Ulla
    Backlund, Ulrika
    Metso, Sundsvall.
    Halvarsson, Sören
    Mittuniversitetet.
    Environmentally friendly process for high density fibreboards2006Conference paper (Other academic)
    Abstract [en]

    Urea-formaldehyde (UF) resin is a common binder in many fibre- and particleboards today. However, formaldehyde is a fairly reactive compound with many negative affects on health and environment. This paper describes a process to make thin high density fibreboards without use of conventional resin such as UF. Initially we found that wood particles such as ones used in particle board had, when activated with hydrogen peroxide and iron catalyst, self-bonding capability when hot-pressed into boards. Low swelling board, although at somewhat higher density than conventional glued ones, could be formed by pressing activated wood particles at 170 oC in a laboratory press. We found that the activation technique was applicable to dry or semi-dry board processes and was considered to be well suited for fibreboards from refined wood fibers especially as their specific (contact) area is high. Activated wood fibres were produced at Metso Panelboards Pilot-refiner in Sundsvall and mats were also formed and pressed into boards 50x60 cm2 at fairly conventional pressing conditions. At a hydrogen peroxide charge of 4% boards made from birch fibres with good mechanical properties (in terms of bending strength and internal bonding) were produced. Thickness swelling in water was low (TS24h., 15-20%). At lower hydrogen peroxide charges (<2%) the swelling was higher. Development of the process to also include other wood species than birch is in our interest. Furthermore, properties of the boards were strongly dependent on the moisture content of fibres; at low moisture content (MC<8%) thickness swelling increased. We see a high potential in the process as the glue-free technique is estimated to reduce production cost of boards as well as give environmental advantages.

  • 13. Li, S.
    et al.
    Lundquist, K.
    Westermark, Ulla
    Cleavage of arylglycerol b-aryl ethers during pulping2000In: 6th European Workshop on Lignocellulosics and Pulp (EWLP 2000): Advances in Lignocellulosics Chemistry Towards High Quality Processes and Products ; Proceedings ; Bordeaux, Sept. 3-6, 2002, Bordeaux: Université Bordeaux , 2000Conference paper (Refereed)
  • 14.
    Li, Shiming
    et al.
    Chalmers University of Technology.
    Lundquist, Knut
    Chalmers University of Technology.
    Westermark, Ulla
    Cleavage of arylglycerol β-aryl ethers under neutral and acid conditions2000In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 15, no 4, p. 292-299Article in journal (Refereed)
    Abstract [en]

    Arylglycerol β-aryl ethers constitute a major type of structure in lignins. Experiments with model compounds representative of such ethers show that the β-ether linkage is broken homolytically on heating under neutral and weakly acid conditions. Cleavage via a benzylic carbocation becomes important when the acidity level is raised.

  • 15.
    Li, Shiming
    et al.
    Department of Organic Chemistry, Chalmers University of Technology.
    Lundqvist, Knut
    Chalmers University of Technology, Department of Forest Products and Chemical Engineering.
    Westermark, Ulla
    Cleavage of syringylglycerol β-syringyl ethers during soda cooking2000In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 15, no 3, p. 205-210Article in journal (Refereed)
    Abstract [en]

    The degradation of model compounds of the syringylglycerol β-syringyl ether type [2-(2,6-dimethoxyphenoxy)-1-(4-hydroxy-3,5-dimethoxyphenyl)-1, 3-propanediol and 2-(2,6-dimethoxy-4-methylphenoxy)-1-(4-hydroxy-3,5-dimethoxyphen yl)-1, 3-propanediol] on soda cooking under comparatively mild conditions was studied. The formation of the degradation products detected, can be envisioned to proceed via a homolytic cleavage of the β-ether bond in an intermediate quinone methide. 2,6-Dimethoxyphenol, sinapyl alcohol, syringaldehyde, 1,2-bis(4-hydroxy-3,5-dimethoxyphenyl)ethanedione, bis(4-hydroxy-3,5-dimethoxyphenyl)methanone and traces of syringyl alcohol were detected in the reaction product obtained from 2-(2,6-dimethoxyphenoxy)-1-(4-hydroxy-3,5-dimethoxyphenyl)-1,3-p ropanediol. 2,6-Dimethoxy-4-methylphenol, sinapyl alcohol, 3-hydroxy-1-(4-hydroxy-3,5-dimethoxyphenyl)-1-propanone, 1-(4-hydroxy-3,5-dimethoxyphenyl)-2-propen-1-one, syringaldehyde and syringyl alcohol were detected in the reaction product obtained from 2-(2,6-dimethoxy-4-methylphenoxy)-1-(4-hydroxy-3,5-dimethoxyphen yl)-1, 3-propanediol. Traces of sinapaldehyde, 2-aryloxyacroleins and, possibly, syringaresinol were present in the reaction mixtures from both model compounds. Reaction routes that explain the differences in product patterns of the two model compounds are presented. The reactions of phenolic arylglycerol β-aryl ethers under the conditions prevailing during alkaline pulping are discussed on the basis of the results

  • 16. Noritsugu, Terashima
    et al.
    Evtugain, Dmitry
    Neto, Carlos Pascoal
    Parkås, Jim
    Paulsson, Magnus
    Westermark, Ulla
    Ralph, Sally
    Ralph, John
    An improved 13C-tracer method for the study of lignin structure and reactions: differential 13C-NMR2003In: Proceedings of the 12th International Symposium on Wood and Pulping Chemistry: University of Wisconsin-Madison, Department of Forest Ecology and Management, June 9 - 12, 2003, Madison, Wisconsin, USA, Madison, Wis., 2003Conference paper (Refereed)
  • 17. Pantze, Anna
    et al.
    Karlsson, Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Westermark, Ulla
    A model system to study esterification reactions in cellulosic or lignocellulosic material2007In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 33, no 4, p. 177-183Article in journal (Refereed)
    Abstract [en]

    The formation of natural ester cross-linkages in cellulosic or lignocellulosic composite materials during drying and heating is of interest for the production of paper and of wood composite boards and in giving cotton materials improved characteristics. A model system has been developed to study quantitatively the esterification of cellulosic material during drying and heating when solid-state conditions can be said to predominate. In the experiments, hexanoic acid and 3-hydroxybutyric acid were added to ordinary filter paper. Moisture content was adjusted, and samples were heated to temperatures ranging from 85 degrees C to 180 degrees C for between 15 and 45 minutes. Quantitative analysis of ester,formation, in this case between the monocarboxylic acids and the cellulose's hydroxyl groups, was performed using aminolysis/gas chromatography. The 3-hydroxybutyric acid was surprising v effective in ester formation. The results indicate that direct esterification of monocarboxylic acid can be an important reaction in lignocellulosic material at elevated temperatures.

  • 18. Pantze, Anna
    et al.
    Karlsson, Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Westermark, Ulla
    Esterification of carboxylic acids on cellulosic material: solid state reactions2008In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 62, no 2, p. 136-141Article in journal (Refereed)
    Abstract [en]

    In the present work, the formation of ester linkages in cellulosic materials during drying and heating was addressed. The results indicated that direct ester formation, without anhydride intermediate, occurs between carboxylic acids of suitable structure and cellulosic hydroxyls at 180 degrees C, even after reaction times as short as 5 min. The 2(R)-hydroxybutyric acid is most effective in ester formation, followed by 2-ketobutyric acid and 3-hydroxybutyric acid. Hexanoic acid is less effective and veratric acid produces no esters at all. At lower temperatures, 2-ketobutyric acid is the most reactive compound. One conclusion is that a hydroxyl or keto group in alpha position of the carboxylic acids favours ester formation. Another finding is that three pyrrolidine structures are produced after esterification and aminolysis of 2-ketobutyric acid. One of the structures indicates that 2-ketobutyric acid is reactive in two positions and could therefore be a potential cross-linker. A critical parameter for ester formation is pH, and the results indicate that pH < 2 strongly favours esterification, whereas almost no esters are produced at pH > 5-6. All experiments were performed in a solid-state model system (on cellulosic filter paper) with low moisture content. Esterification of five carboxylic acids was studied. Samples were heated constantly at 180 degrees C for 5 min or gradually from 22 degrees C to 180 degrees C over periods ranging from 5 to 45 min. Quantitative analysis of ester formation between the monocarboxylic acids and the hydroxyl groups of cellulose was performed by means of aminolysis and gas chromatography.

  • 19. Pantze, Anna
    et al.
    Westermark, Ulla
    Karlsson, Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Formation of ester cross linkage in lignocellulosic materials during drying and heating2005Conference paper (Other academic)
  • 20. Parkås, J.
    et al.
    Paulsson, M.
    Westermark, Ulla
    Tershima, N.
    New methodology for the study of yellowing reactions in lignocellulosic materials1999Conference paper (Other academic)
  • 21.
    Parkås, Jim
    et al.
    Chalmers University of Technology.
    Paulsson, Magnus
    Chalmers University of Technology.
    Li, Shiming
    Chalmers University of Technology.
    Lundquist, Knut
    Chalmers University of Technology.
    Westermark, Ulla
    Photoyellowing behavior of non-phenolic lignin models representative of end groups and β-ether structures2004In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 19, no 2, p. 146-154Article in journal (Refereed)
    Abstract [en]

    Lignin model compounds representative of etherified end groups [(E)-3-(3,4-dimethoxyphenyl)-2-propenl-ol (1), (E)-3-(3,4-dimethoxyphenyl) propenal (2)] and βethers, [1-(3,4-dimethoxyphenyl)-3-hydroxy-2-(2-methoxy- phenoxy)-1-propanone (3), erythiro-1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)- 1,3-propanediol (4)] have been applied to filter paper and subjected to accelerated photoaging with UV/VIS-light. The changes in optical properties were monitored. In case of all the models, the brightness decreased and the b*-value increased as a result of irradiation, which shows that they are sensitive to light simulating sunlight behind window-glass. In the case of the end group models, the photo-products identified were veratraldehyde and veratric acid together with the Z-isomers of the starting materials. In the case of the cinnamyl alcohol 1, photo-oxidation to the cinnamaldehyde 2 was observed. The irradiation of the αt-carbonylic βether 3 resulted in the homolytic cleavage of the CβO bond and a recombination that led to a β-5 dimer [1-(3,4-dimethoxyphenyl)-3-hydroxy-2-(2-hydroxy-3-methoxyphenyl)- 1-propanone] and a β-1 dimer [1-(3,4-dimethoxyphenyl)-3-hydroxy-2-(4- hydroxy-3-methoxyphenyl)-l-propanone]. The monomeric products veratraldehyde, vanillin, acetoveratrone, and 1-(3,4-dimethoxyphenyl)-3-hydroxy-l-propanone were also formed. The only photoproduct conclusively identified in experiments with the arylglycerol-β-aryl ether 4 was veratraldehyde and most of the starting material was unaffected by the irradiation. The addition of a photosensitizer (acetoveratrone) to this type of model prior to irradiation resulted in some increase in discoloration

  • 22.
    Parkås, Jim
    et al.
    Chalmers University of Technology.
    Paulsson, Magnus
    Chalmers University of Technology.
    Terashima, Noritsugo
    Chalmers University of Technology.
    Westermark, Ulla
    Ralph, Sally
    US Forest Products Laboratory.
    Light-induced yellowing of selectively 13C-enriched dehydrogenation polymers (DHPs): Part 1. Side-chain 13C-enriched DHP (α-, β-, and γ-13C)2004In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 19, no 1, p. 29-36Article in journal (Refereed)
    Abstract [en]

    Light-induced yellowing has been studied using side-chain (α, β, and γ) 13C-enriched DHP (dehydrogenation polymer) and quantitative solution state 13C NMR spectroscopy. The DHP was formed from 13C-enriched coniferin using an enzymatic system consisting of β-glucosidase, glucose oxidase, and peroxidase in a pH 6 buffer solution. The DHP was applied to filter paper, irradiated with UV/VIS light and the photodegraded DHP was extracted and analyzed. The NMR study revealed a drastic decrease in the amount of coniferyl alcohol end groups with the formation of end groups of the vanillin type and small amounts of end groups of the vanillic acid type. The results indicated a moderate formation of αcarbonyls, however, no significant decrease in the amount of βO-4 structures in the extractable part of the irradiated DHP could be established, based on difference spectra corresponding to the 13C-enriched DHP.

  • 23.
    Parkås, Jim
    et al.
    Chalmers University of Technology.
    Paulsson, Magnus
    Chalmers University of Technology.
    Terashima, Noritsugo
    Chalmers University of Technology.
    Westermark, Ulla
    Ralph, Sally
    US Forest Products Laboratory.
    Light-induced yellowing of selectively 13C-enriched dehydrogenation polymers (DHPs): Part 2. NMR assignments and photoyellowing of aromatic ring 1-, 3-, 4-, and 5-13C DHPs2004In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 19, no 1, p. 44-52Article in journal (Refereed)
    Abstract [en]

    Light-induced yellowing of lignocellulosic materials has been studied using 13C-enriched DHP (dehydrogenation polymer), selectively 13C-enriched at positions 1, 3, 4, and 5 in the aromatic ring, and quantitative solution state 13C NMR spectroscopy. The NMR study confirmed the results of previous studies using side-chain labeled DHP, mainly that coniferyl alcohol end groups are degraded with the subsequent formation of α-carbonylic structures, e.g. vanillin end groups. The developed technique renders the potential to follow chemical changes of aromatic carbons 1, 3, 4, and 5, independently from each other. Although a drastic photoyellowing of the sheets was observed, definitive chemical shifts corresponding to quinoid carbons could not be discerned in the spectra. The reasons for this may be that the amount of quinoid carbons formed was too low to be detected, with the experimental setup used, or that the quinoid photo-products, if formed, were not extractable with the solvent used or had reacted further forming non-quinoid structures.

  • 24.
    Parkås, Jim
    et al.
    Chalmers University of Technology.
    Paulsson, Magnus
    Chalmers University of Technology.
    VanderHart, D.L.
    National Institute of Standards and Technology.
    Westermark, Ulla
    Accelerated light-induced aging of α-, β-, γ-C-enriched cell wall-degydrogeneration polymers studied with solid state C NMR spectroscopy2002In: Journal of wood chemistry and technology, ISSN 0277-3813, E-ISSN 1532-2319, Vol. 22, no 4, p. 199-218Article in journal (Refereed)
    Abstract [en]

    Light-induced aging of lignocellulosic materials was studied. A new technique involving selectively α-,β- and γ-13C-enriched cell wall-dehydrogenation polymers (CW-DHP) and solid state 13C nuclear magnetic resonance (NMR) spectroscopy was used. CW-DHP showed a decrease in the amount of end-groups of both coniferaldehyde and coniferyl alcohol type. It was also found that the end-groups become saturated and that the therminal functionalities

  • 25.
    Parkås, Jim
    et al.
    Chalmers University of Technology, Department of Forest Products and Chemical Engineering.
    Paulsson, Magnus
    Chalmers University of Technology, Department of Forest Products and Chemical Engineering.
    Westermark, Ulla
    Terashima, Noritsugu
    Swedish Pulp and Paper Research Institute, Stockholm.
    Solid state NMR analysis of β-13C-enriched lignocellulosic material during light-induced yellowing2001In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 55, no 3, p. 276-282Article in journal (Refereed)
    Abstract [en]

    Photoyellowing of lignocellulosic materials has been studied with a new technique based on solid state 13C-NMR analysis of 13C-enriched DHP in cell wall tissue. The selectively 13C-enriched cell wall-dehydrogenation polymer (CW-DHP) was prepared directly on differentiating xylem from spruce (Picea abies) at pH 6.0 by administering β-13C-enriched coniferin in an enzymatic system consisting of glucose oxidase, β-glucosidase, and the naturally occurring water-insoluble enzymes remaining in the cell wall. The bonding pattern of the formed CW-DHP was found to be: 42% β-β, β-5, and β-1 substructures; 36% β-O-4 derived substructures; and 22% coniferyl alcohol and coniferaldehyde end-groups. The 13C-NMR analysis of unirradiated and irradiated tissue revealed a decrease in the relative amount of coniferaldehyde and/or coniferyl alcohol end-groups during irradiation. Prolonged irradiation also introduced new signals centered at 37, 70, and 102 ppm. The results indicate that the present technique, with the formation of DHP in a naturally lignifying carbohydrate environment, has the potential of being a valuable tool for the study of structural changes of lignin during light-induced yellowing.

  • 26. Parkås, L.
    et al.
    Paulsson, M.
    Westermark, Ulla
    Hauksson, J.
    Edlund, U.
    Study of light-induced yellowing by solid-state 13C-NMR: Indication of b -O-4 cleavage and end-group removal after prolonged irradiation2000In: 6th European Workshop on Lignocellulosics and Pulp (EWLP 2000): Advances in Lignocellulosics Chemistry Towards High Quality Processes and Products ; Proceedings ; Bordeaux, Sept. 3-6, 2002, Bordeaux: Université Bordeaux , 2000Conference paper (Refereed)
  • 27. Sundqvist, Bror
    et al.
    Karlsson, Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Westermark, Ulla
    Determination of formic-acid and acetic acid concentrations formed during hydrothermal treatment of birch wood and its relation to colour, strength and hardness2006In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 40, no 7, p. 549-561Article in journal (Refereed)
    Abstract [en]

    Formation of benzyl esters from acetic and formic acids during heat treatment of birch at 160-200°C has been studied by gas chromatography. High concentrations of formic and acetic acids formed by the wood itself during hydrothermal treatment were found. The concentrations of acids increased with both treatment time and temperature. The maximum formic- and acetic acid concentrations found at 180°C and after 4 h of treatment performed in this work were 1.1 and 7.2%, based on dry-weight wood, respectively. The treated wood material was characterised by mechanical testing [bending tests perpendicular to the grain, modulus of rupture, modulus of elasticity, Brinell hardness, impact bending and colour measurements (CIE colour space)]. The experiments, where high concentration of acids was formed, showed severe losses in mass and mechanical strength. Indications of possible enhanced mechanical properties for the treated, compared with untreated birch wood were found around 180-200°C at short treatment times. This paper discusses possible degradation reactions coupled with the colour and mechanical properties in relation to acid formation, and suggestions for process optimisations.

  • 28.
    Sundqvist, Bror
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Westermark, Ulla
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Eriksson, Gustav
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Cellulose degradation during hydrothermal treatment of birch wood (Betula pubescens Ehrh.)2006In: Cellulose Chemistry and Technology, ISSN 0576-9787, Vol. 40, no 3-4, p. 217-221Article in journal (Refereed)
    Abstract [en]

    Study of cellulose degradation during wood's heat treatment showed a considerable degradation in both commercially and laboratory heat-treated wood samples, probably due to the low pH induced by the heat treatment. Experimental series were performed for investigating cellulose degradation in birch wood, at different pH levels and times, during heat treatments performed at pH values of 4, 7 and 10, for 3 and 6 hours at 180°C. The results show that the selected span of pH and time of treatment clearly affects the size of the cellulose molecules. Study of cellulose degradation involved intrinsic viscosity measurements on α-cellulose from the samples. As a result of heat treatment, viscosity drops from 1430 mL/g (untreated wood) to less than or equal 700 mL/g and less than or equal 350 mL/g, for durations of 3 and 6 hours, respectively. The wood buffered in an aqueous solution at pH 4 showed a drop in intrinsic viscosity around 880 mL/g, while a sample of commercial "thermowood" yielded an intrinsic viscosity of 732 mL/g. For neutral and alkaline pH values, the drop in viscosity is considerably lower. At pH values of 7 and 10, a 3 hr treatment had almost no effect on the degree of polymerisation, while a 6 hr treatment gave intrinsic viscosities around 1000 mL/g and 1216 mL/g, respectively. There is a distinct relation between cellulose's molecular size and wood's strength properties. The decrease in cellulose length in unbuffered systems may affect the strength properties of the treated wood. The experiments show that pH is an important factor to consider.

  • 29.
    Terashima, Noritsugu
    et al.
    2-610 Uedayama, Tenpaku, Nagoya.
    Akiyama, Takuya
    USDA ARS, US Dairy Forage Res Ctr, Madison, WI.
    Ralph, Sally
    Forest Products Laboratory, Madison, WI.
    Evtuguin, Dmitry
    Universidade de Aveiro.
    Neto, Carlos Pascoal
    Universidade de Aveiro.
    Parkas, Jim
    Chalmers University of Technology, Department of Forest Products and Chemical Engineering.
    Paulsson, Magnus
    Chalmers University of Technology.
    Westermark, Ulla
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Ralph, John
    University of Wisconsin.
    2D-NMR (HSQC) difference spectra between specifically C-13-enriched and unenriched protolignin of Ginkgo biloba obtained in the solution state of whole cell wall material2009In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 63, no 4, p. 379-384Article in journal (Refereed)
    Abstract [en]

    In the structural analysis of lignins by 13C-NMR, signal overlap limits definitive assignment and accurate intensity measurement. Selective labeling by 13C-enrichment of a specific carbon in lignin enhances its signal intensity in the spectrum. Further enhancement of the specifically labeled carbons can be realized via difference spectra created from the enriched and unenriched samples. Difference 2D 13C-1H correlation (HSQC) NMR spectra, derived from the spectra of specifically 13C-enriched lignin model polymers (so-called dehydrogenation polymers) and their unenriched counterparts, take advantage of the enhanced dispersion afforded by both 13C and 1H chemical shifts, diminishing the difficulties arising from the signal-overlap problem and aiding in definitive signal assignments. In this research, protolignin in xylem cell walls was specifically 13C-enriched at all of the individual phenylpropanoid side-chain carbons by feeding 13C-enriched coniferins to growing stems of Ginkgo biloba. The whole xylem fractions containing 13C-enriched and unenriched protolignins were dissolved in a mixture of N-methylimidazole and DMSO, and then acetylated. Solution state 2D-NMR (HSQC) spectra of the acetylated whole cell wall were acquired. Difference spectra between the walls containing 13C-enriched and unenriched lignins afforded simplified 2D spectra in which well-separated signals were assigned exclusively to the specifically enriched carbons. This novel NMR technique provides a useful tool for elucidation of entire protolignin in the cell wall of ginkgo xylem.

  • 30. Terashima, Noritsugu
    et al.
    Hafrén, Jonas
    Westermark, Ulla
    VanderHart, D.L.
    Nondestructive analysis of lignin structure by NMR spectroscopy of specifically 13C-enriched lignins: Part 1. Solid state study of ginkgo wood2002In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 56, no 1, p. 43-50Article in journal (Refereed)
    Abstract [en]

    Guaiacyl-type lignin is the major component of ginkgo lignin. Specific 13c-enrichment of α, β and γ-carbons of the guaiacylpropane side chains was achieved by administration of coniferin-[α13C], coniferin-[β-13C] and coniferin-[γ13C], respectively, to growing stems of ginkgo trees. Unenriched coniferin was administered as a control. The xylem tissues containing specifically 13C-enriched lignins or unenriched lignin were subjected to analysis by solid state NMR. Subtraction of the spectrum of tissue containing unenriched lignin from the spectra of tissues containing 13C-enriched lignins gave difference spectra exclusively assigned to the enriched side chain carbons of intact protolignin in the cell walls. From the signal intensities determined under quantitative conditions and an estimate of corresponding standard uncertainties, the percentage ranges of the major inter-unit lignin bonds originating from the β-carbon of the coniferin precursor were estimated to be: β-O-4/α-O-R (R = H, polysaccharides or lignols) including β-OH, 53% to 57%; combined β-5, β-β and β-1, 32% to 36%; coniferaldehyde end groups, 2% to 4%; and coniferyl alcohol end groups, 4% to 6%.

  • 31. Westermark, Ulla
    Fibre surface lignin: technique for labelling of lignin by mercurization prior to ESCA analysis1999In: 10th International Symposium on Wood and Pulping Chemistry: main symposium, Yokohama, Japan, June 7 - 10, 1999 ; 10th Biennial ISWPC, main symposium / [TAPPI Japan], Yokohama, 1999Conference paper (Refereed)
  • 32. Westermark, Ulla
    et al.
    Steenberg, B.
    Sundqvist, Bror
    Impregnation with PEG and solvolysis of wood: reflections from analysis of the ancient warship Vasa2005Conference paper (Other academic)
    Abstract [en]

    The paper raises the question if PEG impregnation of wood is a durable method for preservation of waterlogged items or if unexpected chemical reactions under unfavourable conditions can destroy the impregnated wood. In recent years it has been found that polyethylene glykol is an excellent reagent for solvolysis of wood. This means that polyethylene glycol and low concentration of acid completely and rapidly can degrade wood to low molecular weight products (wood liquefacation).

  • 33. Westermark, Ulla
    et al.
    Sundqvist, Bror
    Basic factors influencing the strength loss in heat treatment processes for production of durable wood2005Conference paper (Other academic)
    Abstract [en]

    Heat treatment of wood leads to improvement of properties such as durability and dimensional stability but also to loss in strength which can be an obstacle for use in wood products. The underlying explanation is often attributed to the degradation of hemicelluloses and lignin. In this work degradation by acid hydrolysis of cellulose is proposed to be a major cause for strength loss in heat treated wood. Hydrothermal treatment was performed at 180°C in a sealed autoclave where the wood samples were soaked in non-buffered and in buffered solutions at pH 4, 7 and 10. Also industrially produced samples of heat treated wood were analysed. The molecular chain length of cellulose was characterized by viscosimetric measurements of dissolved α-cellulose after mild delignification of the samples. The results clearly show that non-buffered systems similar to industrially heat treatment lead to a considerable degradation of cellulose. In the non-buffered systems the pH drops to approximately 3 (room temperature) as a result of heat treatment. Samples from industrially heat treated wood also show cellulose degradation to similar extent as the non-buffered samples. In buffered conditions at pH 7 and pH 10 the degradation of cellulose is clearly diminished. The results indicate that the cellulose degradation can be avoided by modifications that controls or minimizes the effect of acid hydrolysis during the heat treatment process

1 - 33 of 33
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