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  • 451.
    Wågberg, Lars
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Ondaral, Sedat
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Brumer, Harry
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Adsorption of xyloglucan on the smooth celluloses films with different crystallinity2010Ingår i: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 239Artikel i tidskrift (Övrigt vetenskapligt)
  • 452.
    Wågberg, Lars
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Ondaral, Sedat
    Karadeniz Tech Univ, Fac Forestry, Dept Pulp & Paper Technol.
    Enarsson, Lars-Erik
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Hyperbranched polymers as a fixing agent for dissolved and colloidal substances on fiber and SIO2 surfaces2007Ingår i: Industrial & Engineering Chemistry Research, ISSN 0888-5885, E-ISSN 1520-5045, Vol. 46, nr 7, s. 2212-2219Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Hyperbranched polymers (polyesteramides) were used as a cationic fixing agent to remove dissolved and colloidal substances (DCS) from the water phase in a fiber suspension. The relative turbidity, electrophoretic mobility, and average diameter of the colloidal particles were determined as a function of polyelectrolyte concentration. The results indicated that maximum removal of DCS was achieved at about zero electrophoretic mobility of the suspension where the negative surface charges of particles were neutralized by the oppositely charged hyperbranched polymer. The amount of hyperbranched polymers needed to maximize DCS fixation on the fibers was higher than the amount of poly-DADMAC (diallyldimethylammonium chloride) needed to reach the same effect. This was found to be due to the lower molecular weight and lower charge density of hyperbranched polymers. The lower molecular mass allowed penetration of these polymers into pores of fibers that resulted in higher polymer consumption before removal of the dissolved and colloidal substances from the fiber suspensions. A lower charge density further resulted in a higher saturation adsorption of the hyperbranched polymer. Experiments with both DCS and model-latex particles showed that the initial increase in relative turbidity was due to the aggregation of particles before fixation to fibers. The results from quartz crystal microbalance with dissipation (QCM-D) experiments showed that the efficiency of hyperbranched polymer and poly-DADMAC was similar even if they had different structure. Therefore, this study highlights the importance of molecular mass and charge density of the polymers as well as the surface structure of polymer layers which in turn gives implications for development of new structures of fixing agents.

  • 453.
    Wågberg, Lars
    et al.
    KTH, Tidigare Institutioner                               , Fiber- och polymerteknologi.
    Pettersson, G.
    Notley, S.
    Adsorption of bilayers and multilayers of cationic and anionic co-polymers of acrylamide on silicon oxide2004Ingår i: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 274, nr 2, s. 480-488Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Silica surfaces were consecutively treated with copolymers of cationic and anionic polyacrylamides (C-PAM and A-PAM, respectively) and the layer-by-layer build-up was continuously monitored with the aid of stagnation point adsorption reflectometry (SPAR). Four different charge densities of the cationic polymer and one charge density of the anionic polymer were studied. The solid substrate used in the investigation was an oxidized Si wafer, the charge of which was varied by performing the measurements at different pH. Adsorption measurements were performed both in deionized water and with a background electrolyte concentration of 0.01 M NaCl The results show that the adsorption of C-PAM at pH 6 was dominated by electrostatic interactions. However, a significant nonionic contribution to the adsorption of C-PAM on SiO2 was detected-when the results of adsorption measurements conducted in deionized water and in 0.01 M NaCl were compared. At pH 9, the adsorption of C-PAM onto SiO2 was found to be geometrically restricted since the adsorption stoichiometry between the polymer charges and the charges on the surface was less than I irrespective of the charge of the C-PAM. Adsorption of the A-PAM onto the C-PAM covered surface increases as a function of the adsorbed charges in the first layer. Experiments showed that it was possible to form multilayers of polyelectrolytes on the SiO2 surface provided the charge of the C-PAM was high enough. The critical charge of the polyelectrolyte for the formation of multilayers was also dependent on the charge of the substrate; that is, the lower the surface charge the higher the critical charge of the C-PAM. The substrate affected the amount of polyelectrolyte adsorbed up to the fifth layer. For further layers there was almost a stoichiometric relationship between the charges of the polyelectrolytes in consecutive layers. Results from studies of the formed multilayers with a quartz crystal microbalance (QCM-D) indicated that there was a close correlation between energy dissipation into the multilayers and a decrease in the adsorption as detected with SPAR. This in turn indicates that a decrease in the reflectometer signal does not necessarily indicate a decrease in adsorption.

  • 454. Wågberg, Lars
    et al.
    Westerlind, C.
    Spreading of droplets of different liquids on specially structured papers2000Ingår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 15, nr 5, s. 598-606Artikel i tidskrift (Refereegranskat)
    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.

  • 455. Xie, Fei
    et al.
    Lu, Hongduo
    Nylander, Tommy
    Wågberg, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Forsman, Jan
    Theoretical and Experimental Investigations of Polyelectrolyte Adsorption Dependence on Molecular Weight2016Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 32, nr 23, s. 5721-5730Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This work focuses on adsorption of polyions onto oppositely charged surfaces and on responses to the addition of a simple monovalent salt as well as to the polyion length (degree of polymerization). We also discuss possible mechanisms underlying observed differences, of the adsorbed amount on silica surfaces at high pH, between seemingly similar polyions. This involves theoretical modeling, utilizing classical polymer density functional theory (DFT). We furthermore investigate; how long- and-short-chain Versions of the polymer adsorb onto carboxymethylatect cellulose, carrying a high negative charge. Interestingly enough, comparing results obtained for the two different surfaces, we observe an opposite qualitative response for the molecular weight. The large polymer adsorbs more strongly at a silica surface, but for cellulose at low salt levels, there are indications that the trend is opposite. Another difference is the very slow adsorption process observed for cellulose, particularly with short polymers; in fact, with short polymers, we were sometimes unable to establish any adsorption plateau at all. We speculate that the slow dynamics is due to a gradual diffusion of short polymers into the cellulose matrix. This phenomenon could also explain why short-chain polymers seem to adsorb more strongly than long-chain ones, at low salt concentrations, provided that the latter then are too large to enter the cellulose pores. Cellulose swelling at high salt concentrations might diminish these differences, leading to more similar adsorbed amounts or even a lower adsorption for short chains.

  • 456. Xie, Fei
    et al.
    Nylander, Tommy
    Piculell, Lennart
    Utsel, Simon
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Fiberteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Wågberg, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Fiberteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Åkesson, Torbjörn
    Forsman, Jan
    Polyelectrolyte Adsorption on Solid Surfaces: Theoretical Predictions and Experimental Measurements2013Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 29, nr 40, s. 12421-12431Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This work utilizes a combination of theory and experiments to explore the adsorption of two different cationic polyelectrolytes onto oppositely charged silica surfaces at pH 9. Both polymers, poly(diallyldimethylammonium chloride), PDADMAC, and poly(4-vinyl N-methylpyridinium iodide), PVNP, are highly charged and highly soluble in water. Another important aspect is that a silica surface carries a relatively high surface charge density at this pH level. This means that we have specifically chosen to investigate adsorption under conditions where electrostatics can be expected to dominate the interactions. Of specific focus in this work is the response of the adsorption to the addition of simple salt (i.e., a process where electrostatics is gradually screened out). Theoretical predictions from a recently developed correlation-corrected classical density functional theory for polyelectrolytes are evaluated by direct quantitative comparisons with corresponding experimental data, as obtained by ellipsometry measurements. We find that, at low concentrations of simple salt, the adsorption increases with ionic strength, reaching a maximum at intermediate levels (about 200 mM). The adsorption then drops but retains a finite level even at very high salt concentrations, indicating the presence of nonelectrostatic contributions to the adsorption. In the theoretical treatment, the strength of this relatively modest but otherwise largely unknown nonelectrostatic surface affinity was estimated by matching predicted and experimental slopes of adsorption curves at high ionic strength. Given these estimates for the nonelectrostatic part, experimental adsorption data are essentially captured with quantitative accuracy by the classical density functional theory.

  • 457.
    Yun, Sang Ho
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik.
    Lee, Hyung-Seok
    Kwon, Young Ha
    Göthelid, Mats
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik.
    Koo, Sang Mo
    Wågberg, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Fiberteknologi.
    Karlsson, Ulf O.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik.
    Linnros, Jan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik.
    Multifunctional silicon inspired by a wing of male Papilio ulysse2012Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 100, nr 3, s. 033109-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Effective entrapment of air and light is a key element for maintaining stable superhydrophobicity and enhancing anti-reflection or absorption. Inspired by a wing of male Papilio ulysse having a unique structure for enabling effective trapping of air and light, we demonstrate that the structure consisting of well-defined multilayer decorated by nanostructures can be obtained on a silicon wafer by a simple microelectromechanical process, consequently resulted in stable superhydrophobocity under static and dynamic conditions, and strong wideband optical absorption.

  • 458. Zhang, J.
    et al.
    Pelton, R.
    Wågberg, Lars
    Rundlof, M.
    The effect of molecular weight on the performance of paper strength-enhancing polymers2001Ingår i: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 27, nr 5, s. 145-151Artikel i tidskrift (Refereegranskat)
    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.

  • 459.
    Zheng, Guangyuan
    et al.
    Stanford University.
    Cui, Yi
    Stanford University.
    Karabulut, Erdem
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Fiberteknologi.
    Wågberg, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Fiberteknologi. KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center.
    Zhu, Hongli
    University of Maryland.
    Hu, Liangbing
    University of Maryland.
    Nanostructured paper for flexible energy and electronic devices2013Ingår i: MRS bulletin, ISSN 0883-7694, E-ISSN 1938-1425, Vol. 38, nr 4, s. 320-325Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cellulose is one of the most abundant organic materials on earth, and cellulose paper is ubiquitous in our daily life. Re-engineering cellulose fibers at the nanoscale will allow this renewable material to be applied to advanced energy storage systems and optoelectronic devices. In this article, we examine the recent development of nanofibrillated cellulose and discuss how the integration of other nanomaterials leads to a wide range of applications. The unique properties of nanofibrillated cellulose enable multi-scale structuring of the functional composites, which can be tailored to develop new concepts of energy and electronic devices. Tapping into the nanostructured materials offered by nature can offer many opportunities that will take nanotechnology research to a new level.

  • 460. Åvitsland, G.A.
    et al.
    Sterner, M.
    Wågberg, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi, Fiberteknologi.
    Ödberg, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi, Fiberteknologi.
    AKD sizing of TCP and ECF bleached birch pulp characterized by peroxide edge wicking index2006Ingår i: Nordic Pulp and Paper Research Journal, ISSN 0283-2631, Vol. 21, nr 2, s. 237-244Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To study the impact of extractable materials and xylan on the sizing efficiency of totally chlorine-free (TCF) bleached birch pulp and elemental-chlorine-free (ECF) bleached birch pulp, several pulps with different amounts of extractable material were studied. The content of extractable material in the pulp was shown to be detrimental for sizing efficiency, measured both as Cobb60 values and edge penetration in a model liquid packaging board, and a higher content of extractable material causes a reduced sizing efficiency for a given pulp. No significant difference was observed between extracted TCF and ECF bleached birch pulps, while unextracted pulps containing the same amount of extractable material yielded different sizing efficiencies. The TCF bleached birch pulp had a lower sizing efficiency than did the ECF bleached birch, probably because of differences in the fatty acid composition. A greater amount of extractable material also resulted in a smaller fraction of non-extractable alkyl ketene dimers (AKD) relative to the total amount of AKD in the sheet. Enzymatic removal of xylan and thus the reduction of the surface charge had no measurable effect on sizing efficiency. Extracted TCF and ECF bleached pulps only need a content of 0.05 kg/ton non-extractable AKD or 0.08 kg/ton total AKD in the sheets produced to achieve a good sizing effect.

  • 461. Åvitsland, Grete
    et al.
    Sterner, Mirjam
    Wågberg, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Ödberg, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    AKD sizing of TCF and ECF bleached birch pulp characterized by peroxide edge wicking2006Ingår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, nr 2, s. 237-241Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To study the impact of extractable materials and xylan on the sizing efficiency of totally chlorine-free (TCF) bleached birch pulp and elemental-chlorine-free (ECF) bleached birch pulp, several pulps with different amounts of extractable material were studied. The content of extractable material in the pulp was shown to be detrimental for sizing efficiency, measured both as Cobb. values and edge penetration in a model liquid packaging board, and a higher content of extractable material causes a reduced sizing efficiency for a given pulp. No significant difference was observed between extracted TCF and ECF bleached birch pulps, while unextracted pulps containing the same amount of extractable material yielded different sizing efficiencies. The TCF bleached birch pulp had a lower sizing efficiency than did the ECF bleached birch, probably because of differences in the fatty acid composition. A greater amount of extractable material also resulted in a smaller fraction of non-extractable alkyl ketene dimers (AKD) relative to the total amount of AKD in the sheet. Enzymatic removal of xylan and thus the reduction of the surface charge had no measurable effect on sizing efficiency. Extracted TCF and ECF bleached pulps only need a content of 0.05 kg/ton non-extractable AKD or 0.08 kg/ton total AKD in the sheets produced to achieve a good sizing effect.

  • 462.
    Åvitsland, Grete
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik. Billerud Skärblacka AB, Sweden.
    Wågberg, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Flow resistance of wet and dry sheets used for preparation of liquid packaging board2005Ingår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 20, nr 3, s. 345-353Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The present work has shown that an evaluation of the flow resistance of wet and dry sheets can be used to identify how to improve the resistance against edgewise liquid penetration in liquid packaging board. By application of liquid extrusion measurements it was possible to determine the wet and dry structure of liquid packaging board made from CTMP and chemical pulps typically used in the production of packaging board. The expansion of the papers upon wetting induces a large difference between the dry and wet sheet structure, and the wet pore volume is three to four times the dry pore volume. Sheets made from kraft pulps only expand moderately, whereas sheets made from CTMP expand to a higher extent. Both porosities and flow resistances, calculated from pore volumes, display a large impact of both the wet and dry sheet density. From these results it is clear that CTMP sheets resist flow much less than sheets based on kraft pulps, and even considerably reducing the porosity of CTMP sheets only gives a small effect in the magnitude of the flow resistance. Finally at high levels of sizing it will be difficult to compensate changes in sheet structure with an additional size addition in order to prevent liquid penetration.

78910 451 - 462 av 462
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