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  • 1. Andreasson, Bo
    et al.
    Forsström, Jennie
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Wågberg, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    The porous structure of pulp fibres with different yields and its influence on paper strength2003In: Cellulose, ISSN 0969-0239, Vol. 10, no 2, 111-123 p.Article in journal (Refereed)
    Abstract [en]

    The porous structure of the interior of papermaking fibres is a well-known important property of the fibres. Changes of this structure will influence tensile and burst strength of paper formed from the fibres and a change in pore size of the pores within the fibre wall is also important for the ability of molecules to diffuse in and out of the fibre wall. Relevant examples of this latter effect are the removal of lignin during cooking and the addition of performance chemicals during papermaking. In this paper, pore sizes and the pore size distribution of unbleached softwood fibres have been studied. A well-characterised fibre material consisting of laboratory cooked spruce and pine pulp of various lignin contents was used. Pore size and pore size distribution were measured by studies of the relaxation behaviour of 2H in fibres saturated with 2H2O. Beside this the total and surface charge of the fibres were also measured together with strength properties of papers from unbeaten fibres. For both pulps, there is a maximum in pore radius at a yield around 46%. Calculations of fibre wall volume from water retention values and yield levels show that there is a discontinuity in pore radius as a function of the fibre wall volume around a yield of 51%. It is suggested that this discontinuity is caused by the breakdown of the hemicellulose/lignin matrix within the fibre wall at this yield level. The strength of the papers formed from the fibres shows a correlation with the surface charge of the fibres. Based on the change in surface charge with yield and the change in total charge with yield, this correlation is suggested to be due to an opening up of the external part of the fibre wall. This stresses the importance of the chemical composition and physical structure of the outer layer of the fibre wall.

  • 2.
    Andreasson, Ulrika
    et al.
    SCA Packaging Research, Sundsvall, Sweden.
    Wågberg, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Ink release from printed surfaces: new methodology and initial insights to the true mechanisms behind ink detachment2001Report (Other academic)
  • 3.
    Eriksson, Malin
    et al.
    Royal Institute of Technology, Stockholm.
    Torgnysdotter, Annsofie
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Wågberg, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Surface modification of wood fibres using the polyelecrolyte multilayer technique: Effects on fibre joint and paper strength properties2006In: Industrial & Engineering Chemistry Research, ISSN 0888-5885, E-ISSN 1520-5045, Vol. 45, no 15, 5279-5286 p.Article in journal (Refereed)
    Abstract [en]

    Polyallylamine hydrochloride (PAH) and poly(acrylic acid) (PAA) were used to modify wood fibers by means of the polyelectrolyte multilayer (PEM) technique. Hand sheets and fiber crosses were prepared from the PEM-treated fibers. The sheet strength and fiber-fiber joint strength were evaluated, and the contact zone of the fiber-fiber joint was characterized using a recently developed staining technique. The nonjoined surface area of the paper sheets was estimated by determining nitrogen adsorption via BET analysis, and the results were compared with those of the light scattering measurements frequently used to determine the degree of “bonding” in paper. Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy was used to analyze chemical effects. It was shown that the PEM treatment of fibers increased the strength properties of the sheets through an increase in the number of fiber-fiber joints, increasing the degree of contact in a fiber-fiber joint and creating covalent bonding in the fiber-fiber joint.

  • 4.
    Fält, Susanna
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Wågberg, Lars
    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, 69-73 p.Article 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.

  • 5.
    Fält, Susanna
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Wågberg, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Vesterlind, Eva-Lotta
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Swellling of model films of cellulose having different charge densities and comparison to the swelling behavior of corresponding fibers2003In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 19, no 19, 7895-7903 p.Article in journal (Refereed)
    Abstract [en]

    Cellulose model films with different charge densities were prepared by spin-coating dissolved cellulose in N-methylmorpholine-N-oxide onto SiO2 surfaces. The swelling of the model cellulose films due to exposure to solutions of different electrolytes and at different ionic strengths and pH values were studied using QCM-D (quartz crystal microbalance with dissipation monitoring). Results show that at pH 5, there is a swelling of the film at a low electrolyte concentration (10(-4)-10(-2) M), whereas the deswelling of the film was observed at a high electrolyte concentration (10(-1)-1 M). A considerable swelling of the films is seen when they are treated with deionized water with an increasing pH. The swelling of the films is accompanied by an increase in dissipation, that is, a softening of the material, and the deswelling by a decrease in dissipation, that is, a stiffening of the material. Furthermore, exposure of the films to solutions of different electrolytes affected the swelling of the layer. In this respect, the swelling response of Na2SO4 differs from that of NaCl and CaC1(2) by showing simultaneously high swelling and low dissipation values. The results also show that the rate of swelling reaches its lowest value as the electrolyte concentration reaches the detected limit for the deswelling. The QCM-D results are compared to the swelling of the corresponding carboxymethylated fibers, where a similar behavior was found. However, for the fibers a marked deswelling occurred at a high electrolyte concentration, but only a minor deswelling of the cellulose film was observed. This difference between the materials can be ascribed to noncovalent bonds within the film that will not reform when the swelling forces are decreased at high electrolyte concentrations. A direct measurement of the thickness changes was performed using atomic force microscopy, which shows that the change in frequency measured with QCM-D for the films treated with different NaCl electrolyte concentrations corresponds to changes of 1-2%.

  • 6. Gunnars, S.
    et al.
    Wågberg, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Cohen Stuart, M. A.
    Model films of cellulose: I. Method development and initial results2002In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 9, no 3/4, 239-249 p.Article 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.

  • 7.
    Nilsson, Boel
    et al.
    SCA Graphic research, McGill University.
    Wågberg, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Gray, Derek
    Paprican, McGill University.
    Conformability of wet pulp fibres at small length scales2000Report (Other academic)
  • 8.
    Norgren, Magnus
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Edlund, Håkan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Wågberg, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Aggregation of Lignin Derivatives under Alkaline Conditions. Kinetics and Aggregate Structure2002In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 18, no 7, 2859-2865 p.Article in journal (Refereed)
    Abstract [en]

    The kinetics of kraft lignin (KL) aggregation at alkaline conditions was studied by quasi-elastic light scattering (QELS) and turbidity measurements. Stability ratios (W) for KL were obtained at 70 °C and various concentrations of sodium chloride. By analyzing the early-time evolution data of aggregate growth obtained from QELS, fractal dimensions of flocs formed in both reaction-limited cluster-cluster aggregation regimes and diffusion-limited cluster-cluster aggregation regimes were determined. Correlations between the fractal dimension and the W-ratio were found in accordance to recent studies of a system containing monodisperse polystyrene colloids. By cryogenic transmission electron microscopy, the fractality of KL aggregate structures in the system was also shown. It was seen from stability studies of KL solutions that the effects of specific co- and counterions follow the Hofmeister series. From the outcome of the investigation, different modes of aggregation occurring in a KL system are proposed. Starting from the macromolecular state of KL and evolving through larger aggregates, the KL clusters finally exhibit a supramolecular structure similar to what earlier has been proposed for native softwood lignin.

  • 9. Pelton, R.
    et al.
    Zhang, J.
    Wågberg, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Rundlöf, Mats
    The role of surface polymer compatibility in the formation of fiber/fiber bonds in paper2000In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 15, no 5, 400-406 p.Article in journal (Refereed)
    Abstract [en]

    The tensile strength of unbeaten kraft pulp handsheets was measured as a function of the compatibility of polymers adsorbed on the fibers. Two types of fibers were prepared, one was treated with slightly cationic dextran and the second was treated with slightly hydrophobic cationic dextran. The dextrans were chosen because both are paper strength enhancing polymers and yet they are incompatible with each other. Either dextran alone significantly enhanced paper strength whereas sheets made with mixtures were weaker. The results are interpreted in terms of the polymer compatibility. When a fiber/fiber bond forms between two surfaces bearing incompatible adsorbed polymers, the polymers will not interdiffuse during sheet consolidation thus giving a relatively weak interfiber bond.

  • 10.
    Rundlöf, Mats
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Eriksson, Marie
    Ström, Helene
    Wågberg, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Effect of Mannanase and Lipase on the properties of colloidal wood extractives and their interaction with mechanical pulp fines2002In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 9, no 2, 127-137 p.Article in journal (Refereed)
    Abstract [en]

    The effects of enzymatic treatments of dissolved and colloidal substances (DCS) released from thermomechanical pulp (TMP) have been investigated. A model dispersion of DCS was made by leaching several portions of TMP in distilled water and separating the fibrous material. Some samples were enriched in colloidal particles by removing dissolved substances using ultra-filtration. The DCS, which had been subjected to different enzymatic treatments, were added in a fixed quantity to TMP fines that had been made cationic, and were subsequently used to form handsheets. All DCS additions increased the content of lipophilic extractives in the sheets. Lipase gave a complete hydrolysation of triglycerides into free fatty acids. The untreated DCS gave no significant decrease in tensile strength, because of the relatively small addition. A treatment of the DCS with Lipase gave a higher extractives content and a tensile strength on the same level as the reference. A Mannanase treatment gave a decrease in strength compared with the reference at the same amount of extractives in the sheet. A combined treatment with Mannanase and Lipase gave a more pronounced decrease in tensile strength. Two possible reasons for the differences in strength at a given amount of extractives were suggested: (i) the destabilisation of the colloidal wood extractives due to the Mannanase could affect the distribution of the colloid in the sheet, making it more detrimental to sheet strength compared with the stable colloid. This would account for the observation that Lipase did not affect sheet strength as such, but the combination with Mannanase gave the lowest tensile strength; (ii) the decomposition of galactoglucomannans in aqueous solution would diminish their positive effect on tensile strength and/or affect the adsorption of the colloid. A reflectometry technique was used to quantify the adsorption of the differently treated DCS onto a model surface of the cationic fines. Colloidal wood extractives were identified on the surfaces after adsorption using staining and light microscopy. No variations in adsorbed amounts were found that could explain the differences in sheet strength, which indirectly suggests that the distribution of the colloid over the surface was affecting the ability of a strong bonded joint to be formed between two such surfaces.

  • 11. Rundlöf, Mats
    et al.
    Karlsson, M.
    Wågberg, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Poptoshev, E.
    Rutland, M.
    Claesson, P.
    Application of the JKR method to the measurement of adhesion to Langmuir-Blodgett cellulose surfaces2000In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 230, no 2, 441-447 p.Article in journal (Refereed)
    Abstract [en]

    The JKR method has been applied for studying adhesion between poly(dimethylsiloxane) (PDMS) caps and Langmuir-Blodgett cellulose surfaces including the substrate, hydrophobized mica, and two flat mineral surfaces, bare mica and glass, The self-adhesion of PDMS caps and oxidized PDMS caps are included as a reference to compare with literature data. The results of the measurements have been compared with previous studies using the surface force apparatus and similar systems. A satisfactory agreement is obtained for simple systems showing no, or very limited, hysteresis between loading and unloading curves, In several cases, however, a large hysteresis is found between loading and unloading curves, with a larger adhesion measured from the pull-off force than from the JKR-curve determined on loading. This is, for instance, the case for PDMS against cellulose. The situation is analogous to that found in wetting studies showing a large hysteresis between advancing and receding contact angles. (C) 2000 Academic Press.

  • 12.
    Rundlöf, Mats
    et al.
    SCA Graphic Research.
    Karlsson, Marie
    PRV.
    Wågberg, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Poptoshev, Evgeni
    YKI.
    Rutland, Mark
    YKI.
    Claesson, Per
    YKI.
    Application of the JKR method to the measurement of adhesion to Langmuir-Blodgett cellulose surfaces2000Report (Other academic)
  • 13. Rundlöf, Mats
    et al.
    Sjolund, A. K.
    Strom, H.
    Asell, I.
    Wågberg, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    The effect of dissolved and colloidal substances released from TMP on the properties of TMP fines2000In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 15, no 4, 256-265 p.Article in journal (Refereed)
    Abstract [en]

    An experimental method to manufacture a model "white water" from mechanical pulp by leaching of the pulp in distilled water is presented. This water, which contains dissolved and colloidal substances "DCS", is fractionated into two fractions: a fraction which contains solely dissolved substances, "DS", and a fraction enriched in colloidal particles, "CS". The major part of the lipophilic extractives were found in the "CS" fraction and had a similar composition as the extractives in the non-fractionted water sample, the "DS" fraction contained no detectable amounts of neutral components and small amounts of fatty and resin acids. Galactoglucomannan was the dominating dissolved polysaccharide, Arabinose or Xylose were not detected in the water. The effect of these types of "white water" on the characteristics of TMP was studied by addition of different amounts to cationised TMP fines prior to sheet making. Fines were chosen as a model system because they are probably more susceptible to adsorption of "DCS" than coarser fractions, due to higher specific surface area. It was shown that water containing colloidal particles decreased the tensile strength of handsheets and that this decrease becomes more pronounced if the addition of colloial particles is increased. It is suggested that this decrease is linked to the amount of lipophilic extractives present on the surface of the fines and it is shown that the decrease begins to occur at a surface coverage of about 45%, as calculated from ESCA data. The tensile index was not affected by addtion of "DS" under the experimental conditions used. The light absorption coefficent of the sheets increased upon addition of all water fractions, which indicates that the dissolved substances are an important reason for the observed darker colour.

  • 14. Solberg, D.
    et al.
    Wågberg, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    On the mechanism of GCC filler particle retention during dewatering - New techniques and initial findings2000Conference paper (Refereed)
    Abstract [en]

    The main objective of this present investigation was to clarify the mechanism of ground calcium carbonate (GCC) retention during dewatering through a thick pad of pulp fibers. It has earlier been claimed that mechanical filtration of aggregated filler particles during dewatering and the deposition of filler particles onto the fiber surface prior to dewatering, are the main filler retention mechanisms. In the present study, the effect of filtration was studied by examining the filler particle size distribution before and after filtration of a filler suspension through a thick pad of pulp fibers. Changes in the wet-web pore size distribution in beds with and without filler were measured by liquid porosimetry. The filler distribution through the bed was obtained from SEM micrographs. The results indicate that deposition on fibers is the dominant process for the retention of commercial GCC particles with a mean particle size of 0,6 and 0,8 μm. Only a marginal fraction of these particles are retained by filtration even though the experimental conditions (laminar flow and a very high grammage) were chosen to favour such process. These results are valid for well-dispersed, non-flocculated GCC particles.

  • 15.
    Solberg, Daniel
    et al.
    SCA Packaging Research.
    Wågberg, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    On the mechanism of GCC filler particle retention during dewatering: new techniques and initial findings2000Report (Other academic)
  • 16.
    Wågberg, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Polyelectrolyte adsorption on cellulose fibres: a review2001Report (Other academic)
  • 17.
    Wågberg, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Polyelectrolyte adsorption onto cellulose fibres - A review2000In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 15, no 5, 586-597 p.Article in journal (Refereed)
    Abstract [en]

    This review focuses upon the following questions: a) Why are the polyelectrolytes adsorbed onto cellulosic fibres? The easiest way to describe the adsorption is as an interaction between the charges on the fibres and the charges on the polyelectrolytes. However the entropy gain upon the release of counterions to the charges on the fibres and the polyelectrolytes gives a much larger contribution to the adsorption energy than the charge interaction. There are some investigations which clarify the influence of certain basic parameters on the fibres and the surfaces and these investigations will be reviewed. An attempt will also be made to create a link between published adsorption data and the Scheutjens-Fleer theory for polyelectrolyte adsorption. Another important question is how the polyelectrolytes are adsorbed on the fibres, i.e. are the segments only found in trains on the surface or will there be some loops and/or tails protruding into the solution? Very little is known about this but the topic will be discussed in some detail. b) Where are the polyelectrolytes adsorbed - on the external surfaces of the fibres or within the fibre wall and how is this related to the molecular properties of the polyelectrolytes? There are a lot of definitions in the literature about fibre surfaces, external surfaces etc. but it is important to link the adsorption to molecular properties and the work in this area will be reviewed. The influence of fines will also be discussed. c) What controls the kinetics of polyelectrolyte adsorption and are there models to describe this adsorption? It is still not entirely known how polymers that adsorb onto the internal surfaces of the fibres are then transported through the fibre wall. The work conducted in this area will be reviewed, It is also important to know the kinetics of the reconformation of the polymer on the fibre surface and this topic will also be discussed in detail. Finally the kinetics of desorption will be treated.

  • 18.
    Wågberg, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Spreading of droplets of different liquids on specially structured papers2000Report (Other academic)
  • 19.
    Wågberg, Lars
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Hägglund, R
    SCA Packaging Research.
    Kinetics of polyelectrolyte adsorption on cellulosic fibers2001In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 17, no 4, 1096-1103 p.Article in journal (Refereed)
    Abstract [en]

    The present investigation has been focused on studying the adsorption of three different molecular mass fractions of a polydimethyldiallylammonium chloride (DMDAAC) (8750 (LMw), 48 000 (MMw), and 1 200 000 (HMw)) on bleached chemical fibers. Both kinetics of adsorption and equilibrium adsorption measurements have been conducted, and the adsorption has been measured by polyelectrolyte titration. The results show that the LMw polymer can reach all the charges in the fiber wall whereas the MMw and HMw can only reach the charges on the external surfaces of the fibers. It is also shown that the kinetics of adsorption of the LMw polymer is not at all affected by the presence of a saturated layer of HMw polymer on the surface of the fibers. Finally the results from the investigation show that it is possible to have a full coverage of the external surface of the fibers by a high molecular mass polymer and a full coverage of the internal surface of the fibers with a low molecular mass polymer provided that the high molecular mass polymer is adsorbed before addition of the low molecular mass polymer. This is true if the polymers are adsorbed to the same type of groups on the fibers. A simplistic model for describing ployelectrolyte adsorption in turbulent flow also shows good agreement with measured values for the low molecular mass polyelectrolyte whereas the agreement for the high molecular polyelectrolyte is not as good. For the high molecular mass polyelectrolyte a more sophisticated model is needed.

  • 20.
    Wågberg, Lars
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Hägglund, Rickard
    SCA packaging Research.
    Kinetics of polyelectrolyte adsorption on cellulosic fibres2000Report (Other academic)
  • 21.
    Wågberg, Lars
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Westerlind, Christina
    SCA.
    Spreading of droplets of different liquids on specially structured papers2000In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 15, no 5, 598-606 p.Article in journal (Refereed)
    Abstract [en]

    The spreading kinetics of drops of different liquids (water, glycerol and ethylene glycol) on different types of model papers have been investigated. In the first part of the investigation single ply and two-ply papers, made from pulps with different degrees of beating, were investigated. The results show that is very common the surface layer of the paper had a much larger influence on the spreading than the bottom ply. By normalising the data showing the drop radius as a function of time with the viscosity and surface tension of the liquids all data collapse onto a master curve. The results from the first part of the investigation also show that in order to determine a contact angle between the liquid and the paper the drop volume should remain constant and the contact angle should be determined when the drop has reached its equilibrium volume. In the second part of the investigation the influence of surface topography and surface energy of the papers on the spreading kinetics was determined. The results show that when the pattern of use, the avails on the surface creates fine capillaries the contact angle is decreased compared to the situation with a flat surface. For papers with a higher roughness the uneven structure creates barriers against the spreading which increases the contact angle compared to the situation with a flat surface. A simple attempt to fit the data to a power law based on a hydrodynamic approach was also conducted. The results from this treatment show that it is possible to get a good match for the sheets with virtually only surface spreading. The constants achieved in this treatment can be used to rationalise the spreading data to be compared with other investigations.

  • 22.
    Zhang, Jin
    et al.
    McMaster Ctr. for Pulp/Paper Res., Department of Chemical Engineering, McMaster University, Hamilton, Ont. L8S 4L7, Canada.
    Pelton, Robert
    McMaster Ctr. for Pulp/Paper Res., Department of Chemical Engineering, McMaster University, Hamilton, Ont. L8S 4L7, Canada.
    Wågberg, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Rundlöf, M.
    SCA Research AB, SE-850 03 Sundsvall.
    The effect of molecular weight on the performance of paper strength-enhancing polymers2001In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 27, no 5, 145-151 p.Article in journal (Refereed)
    Abstract [en]

    The influence of dextran molecular weight (77 000 to 2 000 000) on the strength of fibre-fibre bonds was investigated. A series of cationic dextrans with different molecular weights, from 77 000 to 2 000 000, was prepared and the adsorption behaviour on fibre was characterized. The maximum amount of adsorbed dextran increased with decreasing molecular weight, while the adsorbed layer thickness on colloidal silica increased with increasing molecular weight. At saturation coverage, the molecular weight of dextran did nor affect the tensile strength of handsheets made from unbeaten bleached kraft pulp. The strength improvement with polymer addition did not correspond to increased optical bonded area (opacity). The external surface of fibre accessible to dextran of molecular weight 2 000 000 was estimated as 35 m(2)/g.

  • 23. Zhang, Jin
    et al.
    Pelton, Robert
    Wågberg, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Rundlöf, Mats
    The effect of charge density and hydrophobic modification on dextran-based paper strength enhancing polymers2000In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 15, no 5, 440-445 p.Article in journal (Refereed)
    Abstract [en]

    The dry tensile strengths of bleached kraft pulp handsheets were measured as functions of the cationic charge density and hydrophobic substituents on 2 million Dalton dextran adsorbed onto the fibers before sheet making. The charge density controlled the maximum amount of dextran that could be adsorbed by the fibers which, in turn, influenced tensile strength. The lower the charge density, the higher were both the dextran adsorption capacity of fibers and the tensile strength of the resulting paper. Butanoic and hexanoic acid when condensed onto dextran gave hydrophobic domains which lowered paper strength linearly with hydrophobic content. An extension to the Page equation gave a semi-empirical model which predicted the major effects of hydrophobic substitution on paper strength.

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