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  • 1.
    Ankerfors, Caroline
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Lingström, Rikard
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Ödberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    A comparison of polyelectrolyte complexes and multilayers: Their adsorption behaviour and use for enhancing tensile strength of paper2009In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 24, no 1, p. 77-86Article in journal (Refereed)
    Abstract [en]

    This paper compares the adsorption behaviour and paper-strength-enhancing properties of polyelectrolyte complexes (PECs) and polyelectrolyte multilayers (PEMs) of polyallylamine hydrochloride and polyacrylic acid. Model adsorption experiments using SPAR (stagnation point adsorption reflectometry) and QCM-D (quartz crystal microbalance with dissipation) showed that the amount of complexes adsorbed was lower than the amount adsorbed when forming a multilayer using the same polymer system. From these experiments, in combination with AFM and ESEM imaging, it was concluded that the PEC adsorption stopped before full surface coverage was reached. Tensile testing of handsheets treated with PECs and PEM showed a significant increase in both tensile index and strain-at-break using both systems. The largest strength improvement was achieved with the fibres treated with the largest number of PEMs, but the largest effect per adsorbed amount of polymer was achieved by PEC treatment.

  • 2.
    Johansson, Erik
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Blomberg, Eva
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Lingström, Rikard
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Adhesive Interaction between Polyelectrolyte Multilayers of Polyallylamine Hydrochloride and Polyacrylic Acid Studied Using Atomic Force Microscopy and Surface Force Apparatus2009In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 25, no 5, p. 2887-2894Article in journal (Refereed)
    Abstract [en]

    In the present work, the adhesion between substrates treated with identical polyelectrolyte multilayers (PEM) from polyallylamine hydrochloride (PAR) and poly(acrylic acid) (PAA) was studied using atomic force microscopy (AFM) and the Surface force apparatus (SFA). The AFM measurements, conducted under wet conditions for PEMs formed at pH 7.5, showed a higher adhesion (pull-off force) when PAH was adsorbed in the outermost layers. There was also a difference depending on the Molecular mass of the polymers, demonstrating a greater adhesion for the low molecular mass combination of polyelectrolytes. Furthermore, die time in contact showed to be of importance, with increasing pull-off forces with contact time at maximum load. The SFA measurements were conducted under dry conditions, at 100% RH, and under wet conditions for PEMs adsorbed at pH 7.5/3.5. The SFA adhesion measurements showed that under dry conditions, the adhesive forces between two high energetic mica substrates were lowered when they were covered by PEMs before the measurements. The thickness of the adsorbed layers was also measured using SFA. This showed that there was a significant swelling when the dry layers were exposed to 100% RH or to wet conditions. The swelling was higher, indicating a less rigid layer, when PAH was adsorbed in the outermost layer than when the PEM was capped with PAA.

  • 3.
    Lingström, Rikard
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Formation and properties of polyelectrolyte multilayers on wood fibres:  influence on paper strength and fibre wettability2006Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The work in this licentiate thesis examines the adsorption of polyelectrolyte multilayers (PEM) onto wood fibres as a new way to influence the properties of the fibre surfaces and hence the fibres. Fundamental aspects of PEM formation on wood fibres have been studied, and discussed in terms of paper strength and wood fibre wettability.

    PEMs have been formed from three different polymer systems: 1) two strong polyelectrolytes (i.e., fully charged over a wide pH range), polydimethyldiallylammonium chloride (PDADMAC) and polystyrene sulphonate (PSS); 2) polyethylene oxide (PEO) and polyacrylic acid (PAA), formed at low pH and held together by hydrogen bonding; and 3) two weak polyelectrolytes, polyallylamine hydrochloride (PAH) and polyacrylic acid (PAA). The PEMs formed from PDADMAC/PSS and PEO/PAA were studied using Stagnation Point Adsorption Reflectometry (SPAR), with SiO2 as the substrate. This was done to establish the formation of PEMs and, using PDADMAC/PSS, also to predict the influence of salt concentration during PEM formation. The amount of PDADMAC/PSS adsorbed was found to increase with salt concentration up to approximately 0.1 M NaCl. The formation of PEMs from PAH/PAA has already been studied in terms of structure; amount adsorbed, and influence on paper strength.

    Sheets were formed from fibres treated with either PDADMAC/PSS or PEO/PAA PEMs and tested to determine paper tensile strength. Both PEM systems increased the tensile index and strain at break in the range of 100% when approximately 10 layers had been adsorbed. After several PEM layers had been adsorbed, the sheets made of fibres treated with PDADMAC/PSS differed in tensile strength depending on the polymer adsorbed in the outermost layer. A higher tensile strength was detected when PDADMAC rather than PSS was adsorbed in the outermost layer. Sheets made of fibres treated with PEO/PAA displayed a linear increase in strength, independent of which polymer that was adsorbed in the outermost layer.

    The amount of adsorbed PDADMAC/PSS, as analysed using nitrogen and sulphur analysis, respectively, increased linearly, but with a higher amount adsorbed in the first layer. A comparison of the adsorption onto the SiO2-surfaces (SPAR-measurements) and fibres shows some differences. This is apparent both regarding the adsorption in the first layer and in the change in adsorbed amount with salt concentration. Despite this, one can conclude that SiO2 and wood fibres show very similar trends, and that SiO2 can be used as a convenient model surface in predicting PEM formation on wood fibres.

    Individual fibres were also partially treated using a Dynamic Contact Angle Analyser, and the treated and untreated parts were analysed in terms of wettability and surface structure. The differences in wettability are significant, depending on the polymer system used and, with PAH/PAA PEMs, the pH strategy show a large influence in wettability. PDADMAC/PSS and PAH/PAA PEMs both had a large influence on wettability, depending on the polymer adsorbed in the outermost layer, wettability being lower when the cationic polymer was adsorbed in the outermost layer. With the PEO/PAA system, however, the polymer adsorbed in the outermost layer caused no detectable difference. These results, when compared against the paper strength results, indicate that the strongest sheets are formed of the fibres with the lowest wettability. This may be explained in terms of wet adhesion: since the fibre networks are formed in water, lower wettability would give a stronger force between the fibres during consolidation, resulting in a greater contact area and thus probably a stronger dry adhesion between the fibres in the formed sheet. This is furthermore also supported by wet adhesion measurements using Atomic Force Microscopy where PEMs formed from PAH/PAA, show that the pull-off force is increased when PAH is adsorbed in the outermost layer, compared to when PAA is adsorbed in the outermost layer.

  • 4.
    Lingström, Rikard
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    On the Adhesion Between Substrates Covered with Polyelectrolyte Multilayers2008Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    This thesis examines the formation of Polyelectrolyte Multilayers (PEM) on cellulose fibres as a new way of influencing the fibre surface and the adhesion between wood fibres. The aim of the study was to enhance the fundamental understanding of the adsorption mechanisms behind the formation of Polyelectrolyte Multilayers on cellulose fibres; to study how the properties of the layers can be influenced and to show how the properties of the layers influence the adhesion between the fibres and the strength of paper sheets made from the PEM treated fibres.

    Different polyelectrolyte systems are known to form PEMs with different properties, and in this work two different polymer systems were extensively studied: poly(dimethyldiallylammonium chloride) (PDADMAC) / poly(styrene sulphonate) (PSS), which are both strong polylectrolytes (i.e. are highly charged over a wide range of pH) and poly allylaminehydrochloride (PAH) /poly acrylic acid (PAA), which are both weak polyelectorlytes (i.e. sensitive to pH changes). PEMs were also formed from PAH/ poly(3,4-ethylenedioxythiophene):PSS (PEDOT:PSS), in order to form electrically conducting PEMs on fibres and PEM-like structures were formed from polyethylene oxide (PEO) and polyacrylic acid (PAA).

    In order to study the influence of the PEM on adhesion and paper strength, fibres were treated and used to form sheets which were physically tested according to determine the tensile index and strain at break. Both these systems were studied using different molecular mass fractions. High molecular mass PDADMAC/PSS (>500k/1000k) had a significantly greater influence as a function of the number of layers than low molecular mass PDADMAC/PSS (30k/80k). In contrast, sheets made from high molecular mass PAH/PAA (70k/240k) showed a significantly lower increase in strength than sheets made from low molecular PAH/PAA investigated earlier. Both these systems had a greater influence on paper strength when the cationic polyelectrolyte was adsorbed in the outermost layer. The amount of polyelectrolytes adsorbed on the fibres was determined using polylectrolyte titration (PET) and destructive analytical methods. Adsorption to model surfaces of silicon oxide was studied before the adsorption on fibres, in order to understand the influence on PEM properties of parameters such as salt concentration and adsorption time.

    Adhesion studies of surfaces coated with PAH/PAA using AFM, showed an increase in adhesion as a function of the number of adsorbed layers. The adhesion was higher when PAH was adsorbed in the outermost layers. Individual fibres were also partly treated using a Dynamic Contact Angle analyser (DCA) and were studied with regard to their wettability. In general, the wettability was lower when the cationic polymer was outermost. The level of adhesion and paper strength are discussed in terms of rigidity and wettability and the PEMs demonstrating a large number of free chain ends, a large chain mobility and a low wettability was found to have the greatest influence to adhesion and paper strength.

  • 5.
    Lingström, Rikard
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Johansson, Erik
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Polyelectrolyte Multilayers for Fibre Engineering2009In: The Nanoscience and Technology of Renewable Biomaterials, John Wiley & Sons, 2009, p. 123-148Chapter in book (Refereed)
  • 6.
    Lingström, Rikard
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Notley, Shannon
    Department of Applied Mathematics, Research School of Physical Sciences and Engineering, Australian National University.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Wettability changes in the formation of polymeric multilayers on cellulose fibres and their influence on wet adhesion2007In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 314, no 1, p. 1-9Article in journal (Refereed)
    Abstract [en]

    Individual wood fibres were partly treated with polyelectrolyte multilayers (PEMs) consisting of two different polymer combinations, poly allylamine (PAH)/poly acrylic acid (PAA) and polyethylene oxide (PEO)/PAA in order to study the influence of these polymers on fibre wettability. Single fibres were partly treated and analysed using a so-called dynamic contact analyser (DCA) where the fibres are wet under controlled conditions. When PAH/PAA was used, a stronger influence on fibre wettability was detected when PAH was adsorbed in the outermost layer of the multilayer than when PAA was adsorbed in the outermost layer. The wettability of fibres treated with PAH/PAA PEMs was also influenced by the pH of the adsorption. With the PEO/PAA system, however, the type of polymer adsorbed in the outermost layer caused no detectable difference. Tests of sheets prepared from fibres treated with PEO/PAA showed an increase of about 90% in the tensile index when 9 layers were adsorbed. These and other recently published results from similar experiments using PAH/PAA [S.M. Notley, M. Eriksson, L. Wagberg, J. Colloid Interface Sci. 292 (2005) 29] are compared to the results for the PEM-treated individual fibres. The results indicate that fibres with low wettability contribute to greater paper strength. AFM-force measurements, with the aid of a colloidal probe technique, have also been performed using PAH/PAA, showing that there is also a close correlation between lower wettability of the surfaces and a higher pull-off force between the PEM, treated surfaces, i.e. the flat surface and the colloidal probe. This is valid for the two pH strategies that are used for the formation for the PAH/PAA PEMs, which are studied using AFM-force measurements.

  • 7.
    Lingström, Rikard
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Polyelectrolyte multilayers on wood fibers: Influence of molecular weight on layer properties and mechanical properties of papers from treated fibers2008In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 328, no 2, p. 233-242Article in journal (Refereed)
    Abstract [en]

    This paper compares the influence of the molecular weight of polylelectrolytes forming polyelectrolyte multilayers (PEM) on wood fibers on adhesion and paper strength. Sheets were made from fibers treated with poly(allylamine hydrochloride) (PAH)/poly(acrylic acid) (PAA) of molecular mass 70,000 and 240,000, respectively, and of poly(dimethyldiallylammonium chloride) (PDADMAC)/poly(styrene sulfonate) (PSS) of molecular mass 30,000 and 80,000, respectively. The results were compared to what has recently been reported for PEM formation on fibers using a low-molecular-mass combination of PAH and PAA and a high-molecular-mass combination of PDADMAC/PSS. There was a less significant improvement in the case of the low-molecular-mass PDADMAC/PSS and the high-molecular-mass PAH/PAA. The adsorbed amounts of PAH and PDADMAC were also determined, showing a lower adsorbed amount of the low-molecular-mass PAH than of the high-molecular-mass PDADMAC. The amount of low-molecular-mass PDADMAC was similar to that found for high-molecular-mass PDADMAC/PSS. Individual fibers were partly treated and studied, showing a less significant decrease in wettability with low-molecular-mass PDADMAC/PSS than with the high-molecular-mass combination. The effect of the molecular weight on the adhesion was discussed in terms of the structure and wettability of the PEMs.

  • 8.
    Lingström, Rikard
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Larsson, Per Tomas
    STFI-Packforsk AB.
    Formation of polyelectrolyte multilayers on fibres: Influence on wettability and fibre/fibre interaction2006In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 296, no 2, p. 396-408Article in journal (Refereed)
    Abstract [en]

    Polydimethyldiallylammonium chloride (PDADMAC) and polystyrene sulfonate (PSS) have been used to build-up polyelectrolyte multilayers (PEMs) on chemical soft wood fibres and on SiO2 at various electrolyte concentrations. Adsorption Onto SiO2 was studied using a stagnation point adsorption reflectometer (SPAR), and the adsorbed amount of PDADMAC and PSS on the fibres was determined using nitrogen analysis and Schoniger burning, respectively. The adsorption onto the two substrates was then compared. Paper testing showed that the tensile index (TI) increased by about 90% when 11 layers had been adsorbed, and that there was a correlation between the adsorbed amount and the increase in TI. It was also shown that the particular polymer present in the outermost layer significantly influenced the TI, and that PDADMAC produced a higher TI. A correlation between the adsorbed amount and the TI was also found. Individual fibres were partly treated with a PEM and analysed using a dynamic contact angle analyser (DCA) and environmental scanning electron microscopy (ESEM).

  • 9.
    Wistrand, Ingemar
    et al.
    STFI-Packforsk AB.
    Lingström, Rikard
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Preparation of electrically conducting cellulose fibres utilizing polyelectrolyte multilayers of poly(3,4-ethylenedioxythiophene): poly(styrene sulphonate) and poly(allyl amine)2007In: European Polymer Journal, ISSN 0014-3057, E-ISSN 1873-1945, Vol. 43, no 10, p. 4075-4091Article, review/survey (Refereed)
    Abstract [en]

    The primary goal with this work is to create electrically conductive cellulose fibres, this has been done to explore possible new applications for fibre based material. This research uses various methods to create polyelectrolyte multilayers (PEMs) on bleached softwood fibres and on SiO2 model surfaces, by sequentially treating these materials with poly(3,4ethylenedioxythiophene):poly(styrene sulphonate) (PEDOT:PSS) and poly(allyl amine) (PAH). Paper sheets were then produced from the PEM-modified pulp and evaluated in terms of tensile strength, adsorbed amount of polymer, and electrical conductivity. To evaluate the influence of fibre charge on the measured paper properties, pulps of two different initial fibre charge densities were prepared via carboxymethylation. Because of the bluish colour of PEDOT:PSS, the build-up of PEM could be easily followed, since the fibres grew increasingly darker blue throughout the modification sequence. The conductivity of the fibre network increased by 2-3 orders of magnitude when the pulp of a higher fibre charge density was used. This suggests that it is more important to create a fibrous network with a high fibre-fibre joint strength and a large total joined area in the sheet rather than to maximize the adsorbed amount of PEDOT:PSS. A difference in conductivity could also be noted depending on the polyelectrolyte adsorbed in the outer layer, PAH lowered the conductivity compared to PEDOT:PSS. Evaluating the mechanical properties revealed that the use of PEDOT:PSS reduces the tensile strength of the paper. When five double layers had been adsorbed onto the carboxymethylated sample in which PEDOT:PSS formed the outer layer, calculations indicated a 25% decrease in tensile strength compared to that of reference material without PEMs. ESEM studies indicate that PEM treatment produces a significantly changed and somewhat smoother fibre surface.

  • 10.
    Wågberg, Lars
    et al.
    KTH, Superseded Departments (pre-2005), Fibre and Polymer Technology.
    Eriksson, M
    KTH.
    Lingström, R
    KTH.
    Notley, S
    KTH.
    Influence of the internal structure of polyelectrolyte multilayer films on the adhesion between solid substrates2005In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 230, p. U3566-U3567Article in journal (Other academic)
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