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  • 1. Ala-Kaila, K.
    et al.
    Li, Jiebing
    KTH, Superseded Departments, Pulp and Paper Technology.
    Gellerstedt, Göran
    KTH, Superseded Departments, Pulp and Paper Technology.
    Chemical character of the response of softwood kraft pulp towards industrial two-stage oxygen-alkali delignification2004In: Paperi ja puu, ISSN 0031-1243, Vol. 86, no 5, p. 353-358Article, review/survey (Refereed)
    Abstract [fi]

    The transient behavior of residual material affecting the kappa number of softwood kraft pulp (termed residual lignin), was tested experimentally step-wise in an industrial two-stage oxygen-alkali delignification process. The behavior was characterized by leaching the pulps and dividing the residual lignin into four different fractions to represent the wash loss fraction, the easily leachable fraction, the slowly leachable fraction and the stagnant fraction of the lignin in pulp. Further characterization was made regarding the chemical character of these fractions, i.e. residual lignin, extractives, hexenuronic acid, and other chemical structures that contribute to the kappa number of the pulps. The componential delignification response in the two oxygen-alkali reactors and the effects of the leaching operation were comprehensively assessed regarding the behavior of these different pulp components. The results were compared with results obtained earlier for birch kraft pulp originating from the same industrial process and treated using identical experimental procedures. Application: This study gives a new perspective with which to evaluate apparent and actual responses in industrial oxygen-alkali delignification of kraft pulps.

  • 2. Ala-Kaila, K.
    et al.
    Li, Jiebing
    KTH, Superseded Departments, Pulp and Paper Technology.
    Sevastyanova, O.
    Gellerstedt, Göran
    KTH, Superseded Departments, Pulp and Paper Technology.
    Apparent and actual delignification response in industrial oxygen-alkali delignification of birch kraft pulp2003In: TAPPI Journal, ISSN 0734-1415, Vol. 2, no 10, p. 23-27Article in journal (Refereed)
    Abstract [en]

    The time-dependent behavior of material that affects the kappa number of birch kraft pulp was experimentally tested in an industrial, two-stage, oxygen-alkali delignification process. The pulps were leached, and the leached material was divided into four different fractions: the wash loss fraction and the easily leachable, slowly leachable, and stagnant fractions. These fractions were further characterized according to their chemical natures, representing residual lignin, extractives, hexenuronic acids, and other chemical structures contributing to the kappa number of the pulps. The apparent and actual delignification responses in the two reactors and the effects of the leaching operation were thoroughly evaluated based on the behaviors to these different pulp components.

  • 3. Al-Dajani, W. W.
    et al.
    Gellerstedt, Göran
    KTH, Superseded Departments, Pulp and Paper Technology.
    On the isolation and structure of softwood residual lignins2002In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 17, no 2, p. 193-198Article in journal (Refereed)
    Abstract [en]

    Different softwood residual lignins were isolated by acid hydrolysis of kraft and soda Pulps. Complete isolation of lignin Could not be achieved in one hydrolysis step. The yield of lignin varied between 35 and 55%. A more acidic, second hydrolysis step was therefore necessary to isolate almost all the lignin remaining in the Pulp residue, giving a total lipin yield of 91%. Alkaline extraction of the pulp was almost as efficient as acid hydrolysis in isolating residual lignins. However, alkaline extraction gave less pure lignin fractions and there was a clear indication of the existence of lignin-carbohydrate bonds. Pine wood meal was acid-hydrolyzed in the same way as the pulps. After two-stage acid hydrolysis, the combined lignin yield was only 45% of the Klason lignin content, which means that native lignin is more difficult to isolate front wood than residual lignin front a chemical pulp. It is Concluded that the difficulty encountered in isolating residual lignin by acid hydrolysis is a problem of limited accessibility due to a complex carbohydrate network surrounding the lignin.

  • 4. Al-Dajani, W. W.
    et al.
    Gellerstedt, Göran
    KTH, Superseded Departments, Pulp and Paper Technology.
    The effect of polysulphide pre-treatment and cooking parameters on the chemical properties and TCF bleachability of alkaline pulps2001In: Pulp & paper Canada, ISSN 0316-4004, Vol. 102, no 8, p. 44-48Article in journal (Refereed)
    Abstract [en]

    The effect of pre-treating softwood chips with polysulphide on the chemical properties of the resulting pulp has been investigated. During subsequent pulping after such pre-treatment, high alkali content is maintained in the cooking liquor and, consequently, an unbleached pulp with a decreased amount of hexenuronic acid is obtained. As compared to other kraft pulps in this study, a polysulphide pre-treatment gives high cooking field, a high viscosity and brightness for the unbleached pulp and a pulp of good bleachability.

  • 5.
    Asplund, G
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Norman, Bo
    KTH, Superseded Departments, Pulp and Paper Technology.
    Fibre orientation anisotropy profile over the thickness of a headbox jet2004In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 30, no 8, p. 217-221Article in journal (Refereed)
    Abstract [en]

    The fibre orientation anisotropy at various levels of the jet from a model headbox has been investigated. Stiff nylon fibres, 3 mm long, were added at extremely low concentrations to make it possible to observe also the centre of the jet. This meant that fibre interactions, such as floc forming, could not take place. Transparent, parallel walls enclosed the jet where fibre orientation was measured. A thin laser sheet illuminated the jet from the side and a video camera captured the light reflected perpendicularly from the fibres. Using image analysis, the orientation of the fibres was evaluated. A central vane was mounted in the headbox nozzle so the effects of the vane wake could be studied. The results show that the effect a the boundary layers, at the walls of a headbox and at the surface of a vane, was to locally reduce fibre orientation anisotropy. Depending on the vane tip shape, fibre orientation anisotropy could be additionally decreased. Overall, the fibre orientation anisotropy was weakly affected by changes inflow rate and strongly dependent on the contraction ratio in the nozzle; low speed and large contractions produced more anisotropic orientations.

  • 6.
    Athley, Karin
    KTH, Superseded Departments, Pulp and Paper Technology.
    Acid-base properties of and metal ion affinity for oxygen-delignified kraft pulps2000Licentiate thesis, comprehensive summary (Other scientific)
  • 7. Axelsson, P.
    et al.
    Ek, Monica
    KTH, Superseded Departments, Pulp and Paper Technology.
    Teder, A.
    Influence of alkali profiling in birch kraft pulping on QPQP bleachability2004In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 19, no 1, p. 37-43Article in journal (Refereed)
    Abstract [en]

    The influence of different aspects of alkali profiling in the kraft cook on QPQP bleachability of oxygen-delignified birch pulp was investigated. The use of a levelled-out alkali profile was compared to a conventional, and different modifications to the levelled-out alkali profile, like alkali charge, degree of delignification and amount of dissolved organic substance and ionic strength in the cooking liquor were studied. The alkali profile itself was found to have a significant effect where a levelled-out alkali profile showed a superior bleachability compared to a conventional one. The bleachability improved with an increased alkali charge towards the end of the cook, a high kappa number after cooking or by a cooking liquor exchange in order to decrease the amount of dissolved organic substance and the ionic strength towards the end of the cook. When a levelled-out alkali profile was used, the bleachability correlated well with the light-absorption of the lignin in the unbleached pulp, where a pulp with a brighter lignin consumed less peroxide in the QPQP sequence, for the pulp to reach 89% brightness.

  • 8. Axelsson, P.
    et al.
    Ek, Monica
    KTH, Superseded Departments, Pulp and Paper Technology.
    Teder, A.
    The influence of alkali charge and temperature in the kraft cook on the QPQP bleachability and the kappa number composition of birch pulp2002In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 17, no 3, p. 206-212Article in journal (Refereed)
    Abstract [en]

    The main objective of this investigation was to study how the alkali charge and the temperature in the kraft cook influence the QPQP bleachability of oxygen-delignified birch pulp. The bleachability was evaluated as the normalised consumption of bleaching chemicals required to reach a certain light absorption coefficient of the pulp. All the pulps had a kappa number of about 17 after the cook and a kappa number of about 10 after oxygen delignification. The alkali charge significantly affected the bleachability and the best bleachability was obtained for an intermediate level alkali charge ([HO-](initial)=1,35 mol/L, corresponding to an effective alkali charge of 21.6% on wood). An increase in cooking temperature gave only a slight increase in bleachability. The contributions to the kappa number of lignin, hexenuronic acids (HexA) and other non-lignin structures were also investigated. Lignin contributed to about 60% of the kappa number in pulps after the cook, to about 40% in pulps after the oxygen delignification, and to about 30% after QPQP bleaching. Hexenuronic acids contributed between 3.7 to 4.7 kappa number units in all pulps, which makes them the largest contributors to the kappa number in oxygen-delignified and QPQP bleached pulps. Other non-lignin structures, were contributing about 3 kappa number units in pulps after the cook, but decreased to less than I kappa number unit after QPQP bleaching. No great differences in the composition of the kappa number could be seen between pulps produced under different pulping conditions, except that there was a somewhat lower hexenuronic acid content in the pulps produced with the highest alkali charge or at the highest cooking temperature.

  • 9.
    Axelsson, Patrik
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Gellerstedt, Göran
    KTH, Superseded Departments, Pulp and Paper Technology.
    Lindström, Mikael
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Condensation reactions of lignin during birch Kraft pulping as studied by thioacidolysis2004In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 30, no 12, p. 317-322Article in journal (Refereed)
    Abstract [en]

    The influences of kappa number and ionic strength during birch kraft cooking on the extent of lignin condensation have been studied using thioacidolysis and size exclusion chromatography. Thioacidolysis degrades alkyl-aryl ether bonds in lignin while leaving carbon-carbon and diaryl-ether bonds relatively intact. Therefore, the lignin structures not cleaved during thioacidolysis can be considered as relatively stable and may account,, for example,for the slow residual phase delignification in the kraft cook and for differences in bleachability. It was shown that condensed lignin structures are formed in the residual lignin during birch kraft cooking. The relative amount of such structures increased with decreasing kappa number or with increasing sodium ion concentration in the cook. These structures were also found in a xylan-lignin complex isolated from a birch kraft pulp. The condensed structures were only partly reactive during oxygen delignification.

  • 10.
    Barbesta, Fabio
    KTH, Superseded Departments, Pulp and Paper Technology.
    Modelling of rheological properties of coating colours2000Licentiate thesis, monograph (Other scientific)
  • 11.
    Bergander, Anna
    KTH, Superseded Departments, Pulp and Paper Technology.
    Local variability in chemical and physical properties of spruce wood fibers2001Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Wood is well known to be a heterogeneous native materialwith large variations in its composite properties, includingvariations whose origins have not yet been completelyidentified. Traditionally, the macroscopic variations in woodhave received the most attention; for example, the variation indensity from the pith to the bark in trees. On the fiber level,morphological variations, such as width and cell wallthickness, have been studied rather extensively, whereas thevariability in the properties of the cell wall has receivedless attention. The aim of this work was to demonstrate some ofthe variability in the chemical and physical properties offibers in annual rings and their effect on the elasticproperties in the transverse direction of the cell wall.

    Double radial cell walls were shown to express a largevariability in properties within the annual ring. FTIRmicroscopic measurements, combined with multivariate analysis,indicated an increase in the hemicellulose content and adecrease in the lignin content when going from earlywood tolatewood in the annual ring. Some of these variations were dueto an increased thickness and relative contribution of the cellwall layers, whereas some might have been due to a differencein their polymer concentrationin the secondary walls. Fibrilangle measurements, using polarization confocal microscopy andorientation of soft rot cavities, showed a large variability ofthe fibril angles, with a decreasing trend from thefirst-formed earlywood fibers to the middle of the annual ring.Latewood fibers had a lower fibril angle. The variability infibril angles of annual rings containing compression wood wasmore scattered and the fibril angles were generally higher bothin early- and latewood. The transverse elastic modulus wasfound to vary substantially from fiber to fiber, with earlywoodfibers tending to have a higher modulus than transition woodfibers. For example, the experimental transverse elasticmodulus of earlywood fibers was 1.5-3.0 GPa, whereas themodulus of transition wood fibers was 0.7-1.5 GPa. These valueswere lower than those values obtained from mathematical modelsbased upon the elastic properties of cellulose, lignin, andhemicellulose. It was shown, however, that it is possible toreduce the discrepancy between experimental and modeled data byusing lower and more orthotropic elastic constants ofhemicellulose and lignin in the modeling. In contrast to thelongitudinal elastic modulus of wood fibers, the variation inthe transverse elastic modulus between earlywood and transitionwood fibers was found to depend more on the relative thicknessand fibril angle of the S1-layer than on the fibril angle in the S2-layer.

    The main conclusion drawn from these observations was thatthe heterogeneity of the wood material is extensive, evenwithin an annual ring.

    Keywords: Cell walls, Chemical composition, Elasticconstants, Elastic strength, Fiber properties, Fibril angles,Mathematical models, Microscopy techniques,Picea abies, Stiffness, Tensile properties, Woodpolymers, Wood

  • 12.
    Bergander, Anna
    KTH, Superseded Departments, Pulp and Paper Technology.
    Radial mechanical properties of the native wood fibre wall1999Licentiate thesis, comprehensive summary (Other scientific)
  • 13.
    Berthold, Fredrik
    KTH, Superseded Departments, Pulp and Paper Technology.
    Chemical aspects on the degradation of lignin during modified kraft pulping processes1997Doctoral thesis, comprehensive summary (Other scientific)
  • 14.
    Björkman, Ulf
    KTH, Superseded Departments, Pulp and Paper Technology.
    Break-up of suspended fibre networks2003In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 18, no 1, p. 32-37Article in journal (Refereed)
    Abstract [en]

    Suspended fibre networks form when flowing fibre suspensions come to rest. When stresses on such a network increases, the network is broken down and the fibre suspension eventually returns to a flowing condition. Here a series of experiments are described showing that the initiation of this break-down process leads to network-free voids opening up in the direction parallel to the largest compression.

  • 15.
    Björkman, Ulf
    KTH, Superseded Departments, Pulp and Paper Technology.
    Stress generation and transmission in suspended fibre networks2003In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 18, no 1, p. 38-43Article in journal (Refereed)
    Abstract [en]

    Suspended fibre networks are viewed as particulate systems of closely packed non-adherent compressible flocs suspended in an incompressible penetrating matrix. Experiments show that stress chains form upon compression because the flocs stand in the way of each other. If tensile stresses are applied, the. flocs separate without significant resistance. Network voids open up between and parallel to the stress chains. The reason is that the fibres create compressible flocs with a Poisson ratio less than 0.5.

  • 16.
    Brännvall, Elisabet
    KTH, Superseded Departments, Pulp and Paper Technology.
    hydrogen sulphide gas pre-treatment prior to modified kraft cookingManuscript (preprint) (Other (popular science, discussion, etc.))
  • 17.
    Brännvall, Elisabet
    KTH, Superseded Departments, Pulp and Paper Technology.
    The effects of fines content and hydrogen sulphide gas pre-treatment on kraft pulping and the strength of polysulphide pulps2000Licentiate thesis, comprehensive summary (Other scientific)
  • 18.
    Brännvall, Elisabet
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Hakanen, A
    Teder, Ants
    KTH, Superseded Departments, Pulp and Paper Technology.
    Strykepotentialen hos massor från polysulfidkok: Del 1. Variationer i vätesulfid- och hydroxidjonhaltReport (Other academic)
  • 19.
    Brännvall, Elisabet
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Hakanen, A
    Teder, Ants
    KTH, Superseded Departments, Pulp and Paper Technology.
    Strykepotentialen hos massor från polysulfidkok: Del 2. Massa- och fiberegenskaperReport (Other academic)
  • 20. Bäckström, M
    et al.
    Brännvall, Elisabet
    KTH, Superseded Departments, Pulp and Paper Technology.
    Effect of primary fines on cooking and TCF-bleaching1999In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 14, no 3, p. 209-213Article in journal (Refereed)
    Abstract [en]

    When pulp is separated into fibre fractions on the basis of size, the smallest fraction obtained is called fines. Primary fines are found in cooked pulp not subjected to beating and secondary fines are created in the cause of beating. Fines have higher lignin and metal ion contents than the fibre fractions of the pulp. In this study, the effect of the primary fines on cooking and bleaching has been investigated. The results showed that removal of the primary fines during cooking had no positive effect on the delignification. The pulp viscosity at a certain kappa number and the H-factor to reach this kappa number were the same, regardless of whether or not the primary fines were present. However, the primary fines had a profound effect on bleaching when a QP sequence was used. An increase of approximately 2 ISO-brightness units was obtained by removing the primary fines prior to bleaching. Pulps with and without primary fines showed no significant difference in metal ion content or light scattering coefficient. The light absorption coefficient was, however, higher in the pulp with fines. The improved bleachability of the pulps without fines was therefore probably caused by differences in lignin content and in the lignin structure rather than by differences in metal ion content.

  • 21. Christiernin, M.
    et al.
    Henriksson, Gunnar
    KTH, Superseded Departments, Pulp and Paper Technology.
    Lindström, Mikael
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Brumer, Harry
    KTH, Superseded Departments, Biotechnology.
    Teeri, Tuula T.
    KTH, Superseded Departments, Biotechnology.
    Lindström, T.
    Laine, J.
    The effects of xyloglucan on the properties of paper made from bleached kraft pulp2003In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 18, no 2, p. 182-187Article in journal (Refereed)
    Abstract [en]

    Xyloglucan was adsorbed onto bleached soft-wood kraft pulp followed by preparation and analysis of handsheets with respect to sheet formation as well as sheet mechanical and optical properties. Adsorption of xyloglucan was found to be slow. After more than 20 hrs adsorption, equilibrium had not been reached. The amount of xyloglucan adsorbed increased with beating, but neither the rate of adsorption nor the quantity adsorbed was significantly affected by temperature. Xyloglucan was found to be practically irreversibly adsorbed onto the fibres and the effects of xyloglucan on paper sheet properties were investigated after thorough washing of the pulp. The adsorption characteristics of xyloglucan confirm observations by other authors on other cellulose substrates. Tensile index values for handsheets formed with the xyloglucan-containing pulps were higher than those measured for control pulps with a comparable beating degree. The light scattering coefficient was, however, not affected by xyloglucan adsorption. Hence, the increase in tensile strength is attributed to an increased relative bond strength between the fibres. Tensile strength versus tear strength relationship was similar for pulps with and without xyloglucan, but water retention value and dewatering resistance were lower for the xyloglucan treated pulps than for the reference pulps at the same tensile strength. In addition, formation was improved for pulps with adsorbed xyloglucan. The conclusion is that xyloglucan is a promising wet end additive that decreases the necessity for beating of the pulp and improves the formation of paper.

  • 22. Elsander, A.
    et al.
    Ek, Monica
    KTH, Superseded Departments, Pulp and Paper Technology.
    Gellerstedt, Göran
    KTH, Superseded Departments, Pulp and Paper Technology.
    Oxalic acid formation during ECF and TCF bleaching of kraft pulp2000In: TAPPI Journal, ISSN 0734-1415, Vol. 83, no 2, p. 73-77Article in journal (Refereed)
    Abstract [en]

    Formation of oxalic acid during bleaching of softwood kraft pulp was studied. The bleaching agents used were oxygen, hydrogen peroxide, chlorine dioxide, peracetic acid, and ozone. Formation of oxalic acid increased linearly with the reduction in kappa number. However, bleaching with peracetic acid produced less oxalic acid than the other bleaching agents. In ozone bleaching, about one-third of the oxalic acid formed is adsorbed on the pulp and not released until pulp pH is increased during a later stage, where it could combine with calcium ions to produce a calcium oxalate scale.

  • 23. Falt, S.
    et al.
    Wågberg, Lars
    KTH, Superseded Departments, Pulp and Paper Technology.
    Influence of electrolytes on the swelling and strength of kraft-liner pulps2003In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 18, no 1, p. 69-73Article in journal (Refereed)
    Abstract [en]

    In the present paper, the effect of common process electrolytes NaCl, Na2SO4 and CaCl2 on fibre swelling and paper strength has been investigated. Results show that there is an initial increase in the water retention value (WRV) of the fibres when the salt concentration is increased at a pH of 5 in the solution surrounding the fibres. At higher salt concentrations, the WRV decreases. This behaviour is most pronounced for Na2SO4 and smaller for NaCl and CaCl2. The increase in swelling is explained as being due to an increase in pH in the fibre wall and a subsequent increased dissociation of the carboxyl groups during the initial increase in ionic strength. When the electrolyte concentration is further increased, the difference in osmotic pressure between the interior of the fibre wall and the surrounding solution decreases and eventually the pressure difference drops to zero. It is also found that there is no unique relationship between the WRV and the strength of paper formed from the fibres treated with different electrolyte concentrations.

  • 24.
    Fors, Christina
    KTH, Superseded Departments, Pulp and Paper Technology.
    The effects of fibre charge on web consolidation in papermaking2000Licentiate thesis, monograph (Other scientific)
  • 25. Gamble, G. R.
    et al.
    Snook, M. E.
    Henriksson, Gunnar
    KTH, Superseded Departments, Pulp and Paper Technology.
    Akin, D. E.
    Phenolic constituents in flax bast tissue and inhibition of cellulase and pectinase2000In: Biotechnology letters, ISSN 0141-5492, E-ISSN 1573-6776, Vol. 22, no 9, p. 741-746Article in journal (Refereed)
    Abstract [en]

    Flax bast tissue was sequentially extracted using hexane, propanol, methanol and water as solvents and extracts were analyzed using reverse phase HPLC and C-13 NMR. Results indicated a large variety of aromatic constituents including flavonoids and hydroxy-methoxy cinnamic acids linked to oligosaccharides and hydroxy acids through glycosidic linkages. The extracts inhibited cellulase and pectinase activities and can thus influence retting.

  • 26.
    Garoff, Niklas
    KTH, Superseded Departments, Pulp and Paper Technology.
    The Friction between Paper Surfaces2002Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The main objective for the work described in this PhD thesiswas to formulate a friction model to characterize thefrictional behavior of paper. More specifically, the modelshould explain a phenomenon that is typical for paper grades,viz.: that the level of paper-to-paper friction is dependent onthe direction and the number of previous slides. The modelshould also explain the lubricating effect oflow-molecular-mass lipophilic compounds (LLC) that occur inpaper on paper-to-paper friction. Furthermore, the model shoulddescribe the types of forces that influence paper-to-paperfiction and explain the mechanism by which the LLC decreasepaper-to-paper friction.

    This thesis consists of a literature review of the basicconcepts of tribology and a summary of the main results andconclusions from four studies on the frictional characteristicsof paper and a study on the friction and adhesion of cellulosesurfaces together with some unpublished material.

    The purpose of the investigation described in the firstpaper was to explain a phenomenon that is typical for papergrades, viz.: the level of paper-to-paper friction is dependenton the direction and the number of previous slides. Thisbehavior is called“friction hysteresis”by theauthors, and it has its origin in the reorientation of thefibers on the surface of a paper and their alignment relativeto the sliding direction.

    The second paper describes a study that was aimed atidentifying lubricants that occur natively in paper. Filterpapers were impregnated with model compounds representing woodextractives, i.e. low-molecular-weight lipophilic compounds,which are present in wood, pulp and paper, and thepaper-to-paper friction was determined. The results of thatstudy show that a wood extractive must fulfill severalstructural criteria in order to lubricate a paper surface: Itmust have a hydrophilic group that can attach to the papersurface and a linear hydrocarbon backbone of sufficientlength.

    Although it is not specifically stated in the second paper,the authors proposed a type of lubrication by which woodextractives decrease paper-to-paper friction that is, ineffect, boundary lubrication. The purpose of the investigationdescribed in the third paper was to clarify whether woodextractives and other low-molecular-mass lipophilic compoundsthat occur in paper can act as boundary lubricants on papersurfaces. The main objective of that study was to investigatethe role of chemical structure of LLC for their orientationrelative to the paper surface, which is an important criterionfor boundary lubrication. Filter papers were impregnated withmagnesium salts of different lipophilic acids, which were usedfor model compounds for the LLC. The deposited layers ofmagnesium salts were characterized by X-ray photoelectronspectroscopy (XPS) and contact angle goniometry and thefriction of the impregnated paper sheets was determined. Theresults show that the degree of lubrication and the resistanceto wear of the layers of a magnesium salt increased withincreasing chain length and increasing degree of linearity ofthe lipophilic acid. Based on the results of that study and ofearlier studies, it is concluded that boundary lubrication isthe type of lubrication by which low-molecular-mass lipophiliccompounds that occur natively in paper decreasepaper-to-paper-friction.

    In boundary lubrication, surfaces are covered withmonolayers of lubricant molecules that comprise an active headgroup that can attach to the surface, e.g. a carboxyl group,and an inert linear backbone, such as a long saturatedhydrocarbon chain. Such compounds form ordered monolayers onsurfaces, so that the backbone points vertically out of planeof the surface. The friction is then determined by theinteractions between the monolayers, which are weaker than theinteractions between the clean surfaces and this gives a lowerfriction.

    The fourth paper describes a study on the origin of thedifferences in friction levels between different linerboardsbased on recycled fiber (old corrugated container, OCC). Thesheets were subjected to two extraction stages and analyzedwith respect to surface roughness and their content oflow-molecular-mass lipophilic compounds (LLC). The resultsshowed that a high amount of LLC in the sheets lead to lowfriction, due to lubrication.

    The fifth paper describes a study that was aimed atdetermining the types of forces that influence the frictionbetween the surfaces of hydrophilic polymers and explaining themechanism by which boundary lubricants decrease the friction.The adhesion and the friction of model systems was measuredwith atomic force microscopy (AFM) using regenerated cellulosefilms and functionalised AFM tips and the effect of fatty acidsand humidity was investigated. The friction significantlyincreased with increasing humidity and that there was a strongcorrelation between the ability of a fatty acid to form ahydrophobic surface and its lubricating performance. Measuredadhesion forces at high humidity were well predicted bytheoretical models that took into account the effect of theLaplace pressure acting in a water meniscus formed aroundcontact regions due to capillary condensation. The resultsindicated that the degree of capillary condensation may beeffectively suppressed by increasing the hydrophobicity of thecontacting surfaces, causing adhesion and friction to decrease.These results suggest that friction between paper surfacesunder ambient conditions is greatly influenced by the degree ofcapillary condensation. Furthermore, lubrication by fatty acidsis achieved by the formation of a vertically oriented,hydrophobic monolayer that can withstand the stresses duringsliding and increase the hydrophobicity of the paper surfaceand thereby suppress capillary condensation.

    Keywords:Friction, paper-to-paper friction, frictionhysteresis, fibers, orientation, sliding direction, woodextractives, low-molecular-mass lipophilic compounds, boundarylubrication, adhesion, capillary condensation, Laplacepressure, surface forces, JKR theory, gas chromatography-massspectroscopy, X-ray photoelectron spectroscopy, contact angle,atomic force microscopy

  • 27.
    Garoff, Niklas
    KTH, Superseded Departments, Pulp and Paper Technology.
    The Influence of Lipophilic Compounds on the Friction between Paper Surfaces2000Licentiate thesis, comprehensive summary (Other scientific)
  • 28. Gartner, A.
    et al.
    Gellerstedt, Göran
    KTH, Superseded Departments, Pulp and Paper Technology.
    Oxidation of residual lignin with alkaline hydrogen peroxide. Part 1: Changes in hydrophilic groups2000In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 26, no 12, p. 448-454Article in journal (Refereed)
    Abstract [en]

    Residual lignin was isolated from an oxygen-bleached softwood kraft pulp and subjected to oxidation with alkaline hydrogen peroxide in order to study how the degradation of the lignin is influenced by parameters such as time, temperature, addition of stabilizing agents and metal ions. The oxidized lignin samples were analyzed with respect to carboxyl and phenolic hydroxyl content. It was found that the peroxide treatment resulted in a rapid increase in the amount of carboxyl groups, presumably due to the elimination of chromophoric groups. Phenolic hydroxyl groups in the lignin required a higher temperature to be oxidized and this led to the formation of more carboxyl groups. The presence of DTPA and/or Mg (II) stabilized the hydrogen peroxide against decomposition and suppressed the degradation of phenolic groups, while the carboxyl groups remained the same. The addition of transition metal ions to the reaction system resulted in a rapid decomposition of hydrogen peroxide but also in a rapid formation of carboxyl groups and a degradation of the lignin.

  • 29. Gartner, A.
    et al.
    Gellerstedt, Göran
    KTH, Superseded Departments, Pulp and Paper Technology.
    Oxidation of residual lignin with alkaline hydrogen peroxide. Part II: Elimination of chromophoric groups2001In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 27, no 7, p. 244-248Article in journal (Refereed)
    Abstract [en]

    Isolated residual lignin from art oxygen-bleached kraft pulp was subjected to oxidation with alkaline hydrogen peroxide under different time and temperature conditions in both the absence and presence of stabilizing agents and transition metal ions. The resulting lignin samples were analyzed by UV/VIS and FTIR spectroscopy. The analyses demonstrate the occurrence at a temperature as low as 50 degreesC: of a rapid but limited elimination of chromophoric groups, resulting in the formation of carboxyl groups. The presence of DTPA and magnesium ions stabilizes the hydrogen peroxide towards decomposition and the chromophore elimination is improved. At a higher oxidation temperature, 80 degreesC, the effect of added stabilizer(s) is particularly pronounced. Addition of transition metal ions resulted in a rapid decomposition of hydrogen peroxide and the introduction of new chromophoric groups.

  • 30.
    Gellerstedt, Göran
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Al-Dajani, W. W.
    Bleachability of alkaline pulps - Part 1. The importance of beta-aryl ether linkages in lignin2000In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 54, no 6, p. 609-617Article in journal (Refereed)
    Abstract [en]

    Analytical and structural studies were done on different types of alkaline pulps and their isolated residual lignins. Although having the same degree of delignification after cooking, some pulps were easier to bleach than others. All isolated residual lignins were found to contain beta -aryl ether (beta -O-4) structures in reasonable amounts when analysed by thioacidolysis (greater than or equal to 10% of the native lignin value). At decreasing kappa numbers, there was also a corresponding decrease in the amount of beta -aryl ether structures in the residual lignin. Moreover, a high beta -aryl ether content in the unbleached residual lignin after cooking was found to contribute to a better bleachability of the pulp, especially when hydrogen peroxide stages were involved. At the same degree of delignification, the superior bleachability of alkaline sulfite pulps over kraft pulps was shown to be attributable to a higher content of beta -aryl ether linkages in the further type of pulps.

  • 31.
    Gellerstedt, Göran
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Al-Dajani, W. W.
    Some factors affecting the brightness and TCF-bleachability of kraft pulp2003In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 18, no 1, p. 56-62Article in journal (Refereed)
    Abstract [en]

    By varying the cooking conditions, several series of kraft pulps having different brightness levels, i.e. different light absorption coefficients (k), were prepared. A clear correlation between the residual alkali concentration in the black liquor and the k-value was found. The darkening of the pulp (increasing k) was shown to be, in part, due to a higher content of calcium ions that increased lignin redeposition onto the fibers during the cook. Moreover, the production of a bright unbleached pulp (with low k-value) appeared to be beneficial for subsequent TCF-bleaching with hydrogen peroxide.

  • 32.
    Gellerstedt, Göran
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Li, Jiebing
    KTH, Superseded Departments, Pulp and Paper Technology.
    An HPLC method for the quantitative determination of hexeneuronic acid groups in chemical pulps1996In: Carbohydrate Research, ISSN 0008-6215, E-ISSN 1873-426X, Vol. 294, p. 41-51Article in journal (Refereed)
    Abstract [en]

    It has recently been demonstrated that 4-deoxy-L-threo-hex-4-enopyranosyluronic acid (''hexeneuronic acid'') is present in kraft pulps and linked to the xylan backbone. An analytical method for the quantitative determination of hexeneuronic acid groups has now been developed. The procedure involves a selective hydrolysis with mercuric acetate of the glucosidic linkage between the hexeneuronic acid group and the xylan chain, followed by oxidation with periodate to form P-formyl pyruvic acid. The latter is reacted with thiobarbituric acid, and the red-coloured adduct formed is separated by reverse phase HPLC and quantified by measuring the absorbance at 549 nm, Some kraft pulps have been analysed to illustrate the contribution of hexeneuronic acid groups to the total amount of oxidizable structures present in such pulps.

  • 33.
    Gellerstedt, Göran
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Li, Jiebing
    KTH, Superseded Departments, Pulp and Paper Technology.
    Xylan degradation products from birch kraft pulp1995In: Proceedings of the 8th International Symposium on Wood and Pulping Chemistry, Helsinki: Vol. I, 1995, p. 533-540Conference paper (Other academic)
  • 34. Gernandt, Renate
    et al.
    Wågberg, Lars
    KTH, Superseded Departments, Pulp and Paper Technology.
    Gärdlund, L.inda
    Dautzenberg, Herbert
    Polyelectrolyte complexes for surface modification of wood fibres - I. Preparation and characterisation of complexes for dry and wet strength improvement of paper2003In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 213, no 1, p. 15-25Article in journal (Refereed)
    Abstract [en]

    Polyelectrolyte complexes (PEC) were formed between a cationic polyamideamine epichlorohydrine condensate (PAE) and an anionic carboxymethylcellulose (CMC) at different ratios between the polymers, orders of mixing, salt concentrations and polymer concentrations. Initially the polymers were characterised by polyelectrolyte titration (charge), static light scattering (molecular weight, radius of gyration) and measurements with a scanning interferometric refractometer (refractive index). The complexes were characterised by ocular inspection and static light scattering in combination with a special evaluation algorithm allowing an estimation of the geometric form of the complexes. The results show that the initial complexes have a spherical form and that the size is fairly constant over a large range of charge ratios between the polymers, provided the complexes are formed in deionised water. When the charge mixing ratio exceeded neutrality a secondary agglomeration of the initially formed complexes occurred. The presence of salt during PEC formation caused a dependence of the level of aggregation on the mixing ratio, whereby small amounts of NaCl drastically lowered the particle mass at lower mixing ratios. Subsequent addition of salt to PECs formed in water led to a strong swelling of the complex particles and at a critical salt concentration to dissolution.

  • 35.
    Gonzalo Epelde, I.
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Lindgren, C. T.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Lindström, Mikael E.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Kinetics of wheat straw delignification in soda and kraft pulping1998In: Journal of wood chemistry and technology, ISSN 0277-3813, E-ISSN 1532-2319, Vol. 18, no 1, p. 69-82Article in journal (Refereed)
    Abstract [en]

    Kraft and soda delignification kinetics of wheat straw, Triticum aestivum, have been studied as a function of OH- concentration, HS- concentration, and temperature. It was found that about 90% of the lignin is dissolved in the rapid initial phase. The rates of delignification in the bulk and residual phases were found to be similar to those of birch wood, Betula pubescens, The amount of residual phase lignin was found to be considerably less than in birch or spruce, Picea abies, and it was affected by the same factors, A model that accurately describes the delignification of wheat straw was derived.

  • 36. Granstrom, A.
    et al.
    Eriksson, T.
    Gellerstedt, Göran
    KTH, Superseded Departments, Pulp and Paper Technology.
    Roost, C.
    Larsson, P.
    Variables affecting the thermal yellowing of TCF-bleached birch kraft pulps2001In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 16, no 1, p. 18-23Article in journal (Refereed)
    Abstract [en]

    The purpose of this investigation was to identify the most important variables influencing the thermal yellowing of TCF-bleached kraft pulps. The variables studied were: hexenuronic acid content, dry content, temperature, time, pH, and iron content. All these variables influence the process of colour reversion. It was shown that there is a strong relationship between hexenuronic acid content and the magnitude of the colour reversion. Of the conditions investigated, long time (6 days), high temperature (80 degreesC), slightly acidic conditions (pH 4.5) and a moist environment (92% dry content) caused the greatest brightness reversion. At 99% dry content the discoloration was insignificant. Impregnation of handsheets has shown that ferrous ions are more detrimental than ferric ions to the colour formation. It is suggested that the hydrolysis of hexenuronic acid into the known acidic degradation products, 2-furancarboxylic acid and 5-formyl-2-furancarboxylic acid can not be the rate limiting reaction in the colour formation. It is also suggested that new aromatic structures are formed during the thermal yellowing process. Finally it was shown that the discoloration can be partly washed away with water.

  • 37. Granstrom, A.
    et al.
    Gellerstedt, Göran
    KTH, Superseded Departments, Pulp and Paper Technology.
    Eriksson, T.
    On the chemical processes occurring during thermal yellowing of a TCF-bleached birch kraft pulp2002In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 17, no 4, p. 427-433Article in journal (Refereed)
    Abstract [en]

    The aim of this investigation was to survey the reactions taking place during heat-induced yellowing of a TCF-bleached birch kraft pulp bleached according to the sequence O Q P Q (PO). This was done by determining the metal profiles in pulp and aqueous pulp extracts before and after accelerated ageing of pulp. It was concluded that low-molecular substances were formed during heat treatment of the pulp. It was further shown that hexenuronic acid (HexA) groups were hydrolysed during the ageing and that the destruction of HexA significantly lowered the chelating properties of the pulp, implying a liberation of metal ions. Two different procedures to isolate the coloured compounds in an aqueous extract of aged pulp are reported. Analysis of the separated strongly coloured material revealed that manganese and iron as well as some dicarboxylic acids were enriched. It was also concluded that if iron ions were removed without hydrolysing HexA, the brightness stability could be improved. Finally some observations and conclusions from previous work are discussed.

  • 38.
    Granström, Anders
    KTH, Superseded Departments, Pulp and Paper Technology.
    on the thermal yellowing of TCF- bleached birch kraft pulp2001Licentiate thesis, comprehensive summary (Other scientific)
  • 39. Gunnars, S.
    et al.
    Wågberg, Lars
    KTH, Superseded Departments, Pulp and Paper Technology.
    Stuart, M. A. C.
    Model films of cellulose: I. Method development and initial results2002In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 9, no 04-mar, p. 239-249Article in journal (Refereed)
    Abstract [en]

    This report presents a new method for the preparation of thin cellulose films. NMMO (N- methylmorpholine- N-oxide) was used to dissolve cellulose and addition of DMSO (dimethyl sulfoxide) was used to control viscosity of the cellulose solution. A thin layer of the cellulose solution is spin- coated onto a silicon oxide wafer and the cellulose is precipitated in deionised water. The cellulose film is anchored onto the silicon oxide wafer by a saturated polymer layer. Among many different polymers tested, PVAm (polyvinylamine) and G- PAM (glyoxalated- polyacrylamide) worked well. The preparation of cellulose model films described in this paper resulted in films with thicknesses in the range 20- 270 nm and the thickness can be controlled by altering the concentration of cellulose solution by addition of different amounts of DMSO. The films were cleaned in deionised water and were found to be free from solvents by ESCA analysis and contact angle measurements. The molecular weight distribution of the cellulose surface material shows that there is only minor breakdown of the cellulose chains, mainly by cleavage of the longest molecular mass fraction and without creation of low molecular mass oligomers of glucose.

  • 40.
    Gustafsson, Roland
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Ek, Monica
    KTH, Superseded Departments, Pulp and Paper Technology.
    Teder, Ants
    KTH, Superseded Departments, Pulp and Paper Technology.
    Polysulphide pretreatment of softwood for increased delignification and higher pulp viscosity2004In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 30, no 5, p. 129-135Article in journal (Refereed)
    Abstract [en]

    The effect of polysulphide pretreatment under various conditions prior to a kraft cook was investigated for spruce (Picea abies) chips using a technique with a liquor:wood ratio of 67:1 to keep the liquor composition as constant as possible during the pretreatment and cooking phases. If the polysulphidepretreatment is carried out at a very high hydroxide concentration, 1.5 mol OH-/L, three independent positive effects (compared with a corresponding sulphide pretreatment without polysulphide) can be observed: more extensive delignification; higher pulp, viscosity; and higher carbohydrate yield. When the alkali change was changed in the subsequent kraft cook (in the range 0.15-0.60 mol/L), the increase in delignification extent as a result of polysulphide pretreatment was not affected but the relative carbohydrate yield increase was favoured by a higher alkali charge during cooking. On the other hand, the absolute carbohydrate yield is favoured by a intermediate alkali charge.

  • 41.
    Gustafsson, Roland
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Freysoldt, Julia
    KTH, Superseded Departments, Pulp and Paper Technology.
    Teder, Ants
    KTH, Superseded Departments, Pulp and Paper Technology.
    Influence of the alkalinity in polysulphide pretreatment on results of cooking with normal liquor-to-wood ratios2004In: Paperi ja puu, ISSN 0031-1243, Vol. 86, no 3, p. 169-173Article in journal (Refereed)
    Abstract [en]

    The effect of alkalinity in a polysulphide pretreatment on the delignification rate, pulp yield and the pulp viscosity in the following kraft cook was investigated. The results were compared to those with reference pretreatments with a corresponding concentrations of hydroxide and hydrogen sulphide ions. The experiments were carried out at liquor-to-wood ratio of 4:1, and the alkalinity in the pretreatments was varied from 0 to 2.5 mole hydroxide/litre. It was found that when the polysulphide preteatment is performed at very high initial hydroxide concentrations, > 1.5 mole/litre, the delignification rate in the cook is increased. The pulp viscosity was higher than that achieved with the sulphide reference when the pulping was extended to low kappa numbers and when the initial hydroxide ion concentration in the pretreatment was high.

  • 42.
    Gustavsson, Catrin A-S.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Some aspects on extended kraft pulping: the influence of cooking parameters on delignification, bleachability and carbohydrate degradation1999Licentiate thesis, comprehensive summary (Other scientific)
  • 43. Gustavsson, Catrin
    et al.
    Lindgren, Christofer
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Lindström, Mikael E.
    KTH, Superseded Departments, Pulp and Paper Technology.
    A Study of How the Amount of Residual Phase Lignin in Kraft Cooking Depends upon the Conditions in the Cook1997In: Nordic Pulp Paper Research Journal, ISSN 0283-2631, Vol. 12, no 4, p. 225-Article in journal (Refereed)
  • 44.
    Gustavsson, Catrin
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Sjöstrom, Karin
    KTH, Superseded Departments, Pulp and Paper Technology.
    Al-Dajani, Wafa
    KTH, Superseded Departments, Pulp and Paper Technology.
    The influence of cooking conditions on the bleachability and chemical structure of kraft pulps1999In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 14, no 1, p. 71-81Article in journal (Refereed)
    Abstract [en]

    The purpose of this investigation was primarily td investigate how variations in cooking conditions in the kraft pulping of softwood influence the subsequent bleaching, and secondly to study the relationship between the bleaching response and the chemical structure of the pulp. The cooking variables studied were hydroxide ion concentration, hydrogen sulfide ion concentration and cooking temperature. The pulps had the same kappa number after the cook, about 20, and were oxygen delignified to about kappa number 8 before bleaching. The influence of the cooking variables on the TCF-bleachability was studied in an AZQP*- and in a QPQP*-sequence (A=acid treatment, Z=ozone stage, Q=chelating agent stage, P*=peroxide stage with the addition of magnesium ions). All three cooking variables studied influenced the TCF-bleachability, but to different extents. The bleachability was improved by increased temperature for low chemical charges, but not at higher chemical charges. When [HS-] was increased the QPQP*-bleachability was improved but the AZQP*-bleachability was not affected. When [HO-] was varied a bleachability maximum was seen for the intermediate hydroxide ion concentration. The content of hexenuronic acid in the pulp after cooking could be reduced by using high initial [HO-], low initial [HS-] and a long cooking time. A high content of beta-O-4 structures in the unbleached residual lignin was found to contribute to a better bleachability of the pulp. However, the phenolic hydroxyl content could not be related to the bleaching response.

  • 45.
    Gärtner, Anna
    KTH, Superseded Departments, Pulp and Paper Technology.
    Ligninets reaktivitet vid peroxidblekning: inverkan av processparametrar1998Licentiate thesis, comprehensive summary (Other scientific)
  • 46.
    Hakanen, Anders
    KTH, Superseded Departments, Pulp and Paper Technology.
    Några synpunkter på massastyrka hos sulfat- och polysulfidkokad skandinavisk barrved1997Licentiate thesis, comprehensive summary (Other scientific)
  • 47. Hallberg, B. M.
    et al.
    Bergfors, T.
    Backbro, K.
    Pettersson, G.
    Henriksson, Gunnar
    KTH, Superseded Departments, Pulp and Paper Technology.
    Divne, Christina
    KTH, Superseded Departments, Biotechnology.
    A new scaffold for binding haem in the cytochrome domain of the extracellular flavocytochrome cellobiose dehydrogenase2000In: Structure, ISSN 0969-2126, E-ISSN 1878-4186, Vol. 8, no 1, p. 79-88Article in journal (Refereed)
    Abstract [en]

    Background: The fungal oxidoreductase cellobiose dehydrogenase (CDH) degrades both lignin and cellulose, and is the only known extracellular flavocytochrome. This haemoflavoenzyme has a multidomain organisation with a b-type cytochrome domain linked to a large flavodehydrogenase domain. The two domains can be separated proteolytically to yield a functional cytochrome and a flavodehydrogenase. Here, we report the crystal structure of the cytochrome domain of CDH. Results: The crystal structure of the b-type cytochrome domain of CDH from the wood-degrading fungus Phanerochaete chrysosporium has been determined at 1.9 Angstrom resolution using multiple isomorphous replacement ncluding anomalous scattering information. Three models of the cytochrome have been refined: the in vitro prepared cytochrome in its redox-inactive state (pH 7.5) and redox-active state (pH 4.6), as well as the naturally occurring cytochrome fragment. Conclusions: The 190-residue long cytochrome domain of CDH folds as a beta sandwich with the topology of the antibody Fab V-H domain. The haem iron is ligated by Met65 and His 163, which confirms previous results from spectroscopic studies. This is only the second example of a b-type cytochrome with this ligation, the first being cytochrome b(562). The haem-propionate groups are surface exposed and, therefore, might play a role in the association between the cytochrome and flavoprotein domain, and in interdomain electron transfer. There are no large differences in overall structure of the cytochrome at redoxactive pH as compared with the inactive form, which excludes the possibility that pH-dependent redox inactivation results from partial denaturation. From the electron-density map of the naturally occurring cytochrome, we conclude that it corresponds to the proteolytically prepared cytochrome domain.

  • 48. Hallberg, B. M.
    et al.
    Henriksson, Gunnar
    KTH, Superseded Departments, Pulp and Paper Technology.
    Pettersson, G.
    Divne, Christina
    KTH, Superseded Departments, Biotechnology.
    Crystal structure of the flavoprotein domain of the extracellular flavocytochrome cellobiose dehydrogenase2002In: Journal of Molecular Biology, ISSN 0022-2836, E-ISSN 1089-8638, Vol. 315, no 3, p. 421-434Article in journal (Refereed)
    Abstract [en]

    Cellobiose dehydrogenase (CDH) participates in the degradation of cellulose and lignin. The protein is an extracellular flavocytochrome with a b-type cytochrome domain (CYTcdh) connected to a flavodehydrogenase domain (DHcdh). DHcdh catalyses a two-electron oxidation at the anomeric C1 position of cellobiose to yield cellobiono-1,5-lactone, and the electrons are subsequently transferred from DHcdh to an acceptor, either directly or via CYTcdh. Here, we decribe the crystal structure of Phanerochaete chrysosporium DHcdh determined at 1.5 Angstrom resolution. DHcdh belongs to the GMC family of oxidoreductases, which includes glucose oxidase (GOX) and cholesterol oxidase (COX); however, the sequence identity with members of the family is low. The overall fold of DHcdh is p-hydroxybenzoate hydroxylase-like and is similar to, but also different from, that of GOX and COX. It is partitioned into an FAD-binding subdomain of alpha/beta type and a substrate-binding subdomain consisting of a seven-stranded beta sheet and six helices. Docking of CYTcdh, and DHcdh suggests that CYTcdh covers the active-site entrance in DHcdh, and that the resulting distance between the cofactors is within acceptable limits for inter-domain electron transfer. Based on docking of the substrate, cellobiose, in the active site of DHcdh, we propose that the enzyme discriminates against glucose by favouring interaction with the non-reducing end of cellobiose.

  • 49. Hallberg, B. M.
    et al.
    Henriksson, Gunnar
    KTH, Superseded Departments, Pulp and Paper Technology.
    Pettersson, G.
    Vasella, A.
    Divne, Christina
    KTH, Superseded Departments, Biotechnology.
    Mechanism of the reductive half-reaction in cellobiose dehydrogenase2003In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 278, no 9, p. 7160-7166Article in journal (Refereed)
    Abstract [en]

    The extracellular flavocytochrome cellobiose dehydrogenase (CDH; EC 1.1.99.18) participates in lignocellulose degradation by white-rot fungi with a proposed role in the early events of wood degradation. The complete hemoflavoenzyme consists of a catalytically active dehydrogenase fragment (DHcdh) connected to a b-type cytochrome domain via a linker peptide. In the reductive half-reaction, DHcdh catalyzes the oxidation of cellobiose to yield cellobiono-1,5-lactone. The active site of DHcdh is structurally similar to that of glucose oxidase and cholesterol oxidase, with a conserved histidine residue positioned at the re face of the flavin ring close to the N5 atom. The mechanisms of oxidation in glucose oxidase and cholesterol oxidase are still poorly understood, partly because of lack of experimental structure data or difficulties in interpreting existing data for enzyme-ligand complexes. Here we report the crystal structure of the Phanerochaete chrysosporium DHcdh with a bound inhibitor, cellobiono-1,5-lactam, at 1.8-Angstrom resolution. The distance between the lactam C1 and the flavin N5 is only 2.9 Angstrom, implying that in an approximately planar transition state, the maximum distance for the axial 1-hydrogen to travel for covalent addition to N5 is 0.8-0.9 Angstrom. The lactam O1 interacts intimately with the side chains of His-689 and Asn-732. Our data lend substantial structural support to a reaction mechanism where His-689 acts as a general base by abstracting the O1 hydroxyl proton in concert with transfer of the C1 hydrogen as hydride to the re face of the flavin N5.

  • 50.
    Henriksson, Gunnar
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Johansson, G.
    Pettersson, G.
    A critical review of cellobiose dehydrogenases2000In: Journal of Biotechnology, ISSN 0168-1656, E-ISSN 1873-4863, Vol. 78, no 2, p. 93-113Article, review/survey (Refereed)
    Abstract [en]

    Cellobiose dehydrogenase (CDH) is an extracellular enzyme produced by various wood-degrading fungi. It oxidizes soluble cellodextrins, mannodextrins and lactose efficiently to their corresponding lactones by a ping-pong mechanism using a wide spectrum of electron accepters including quinones, phenoxyradicals, Fe3+, Cu2+ and tiiodide ion. Monosaccharides, maltose and molecular oxygen are:poop substrates. CDH that adsorbs strongly and specifically to cellulose carries two prosthetic groups; namely, an FAD and a heme in two different domains that can be separated after limited proteolysis. The FAD-containing fragment carries all known catalytic and cellulose binding properties. One-electron accepters, like ferricyanide, cytochrome c and phenoxy radicals, are, however, reduced more slowly by the FAD-fragment than by the intact enzyme, suggesting that the function of the heme group is to facilitate one-electron transfer. Non-heme forms of CDH have been found in the culture filtrate of some fungi (probably due to the action of fungal proteases) and were for a long time believed to represent a separate enzyme (cellobiose:quinone oxidoreductase, CBQ). The amino acid sequence of CDH has been determined and no significant homology with other proteins was detected for the heme domain. The FAD-domain sequence belongs to the GMC oxidoreductase family that includes, among others, Aspergillus niger glucose oxidase. The homology is most distinct in regions that correspond to the FAD-binding domain in glucose oxidase. A cellulose-binding domain of the fungal type is present in CDH from Myceliophtore thermophila (Sporotrichum thermophile), but in others an internal sequence rich in aromatic amino acid residues has been suggested to be responsible for the cellulose binding. The biological function of CDH is not fully understood, but recent results support a hydroxyl radical-generating mechanism whereby the radical can degrade and modify cellulose, hemicellulose and lignin. CDH has found technical use in highly selective amperometric biosensors and several other applications have been suggested.

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