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Sökning: WFRF:(Wågberg Lars) > (2005-2009)

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51.
  • Gimåker, Magnus, et al. (författare)
  • On The Mechanisms Of Mechano-Sorptive Creep Reduction By Chemical Cross-Linking
  • 2009
  • Ingår i: Advances in Pulp and Paper Research, Oxford 2009. - Lancashire, UK : The Pulp and Paper Fundamental Research Society. - 9780954527266 ; , s. 1001-1017
  • Konferensbidrag (refereegranskat)abstract
    • Despite the technical importance of mechano-sorptive creep in paper, the exact mechanism behind this phenomenon is still not fully understood. In this study it was shown that the mechano-sorptive creep of paper sheets can be significantly reduced by chemical cross-linking through periodate oxidation. The mechanism behind this reduction has been examined through creep measurements of both sheets and individual fibres. For sheets the creep acceleration due to varying humidity was significantly reduced by the chemical cross-linking. For single fibres, however, the creep acceleration was not affected by the chemical crosslinking. In fact the absolute creep rate for the periodate oxidised fibres were higher than that of the reference fibres. This clearly showed that the improvement in mechano-sorptive creep found on a sheet level does not originate from an improved creep resistance for individual fibres but rather from mechanisms operating at the fibre network level. Hygroexpansion and moisture sorption of the sheets during the humidity cycling used for creep testing have also been measured, and the results showed that both was reduced by the periodate oxidation. Reduced moisture sorptivity and hygroexpansion probably minimises stress concentrations at the fibre network level and thereby also the creep acceleration.
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52.
  • Gärdlund, Linda, et al. (författare)
  • Influence of polyelectrolyte complexes on strength properties of papers made from unbleached kraft pulps with different yields
  • 2005
  • Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 20:1, s. 36-42
  • Tidskriftsartikel (refereegranskat)abstract
    • The properties of the materials combined in corrugated board are set to give the board its strength, flexibility and protection towards impact and pressure. The raw material is of course the single fibre but additives that enhance e.g. the wet and dry paper strength are also added. As the strength enhancing additives used today are most efficient between pH 4 and pH 7 there is a need for new types of additives that can be used under alkaline conditions. In the present report polyallylamine hydrochloride (PAH) and polyelectrolyte complexes (PEC) of PAH and polyacrylic acid (PAA) were investigated as strength enhancing additives. The components can be used under alkaline conditions and results showed that PAH alone or incorporated into a PEC gave different effects regarding strength properties of sheets from kraft pulps of different yields. The results showed that by treating the fibres with PEC´s of PAH and PAA it was possible to considerably increase the tensile properties, the Z-strength and the compression strength of papers made from the treated fibres. The results showed an increase of as much as 54 % to 180 % in dry Z-strength and 14 % to 53 % in compression strength, when using the PEC as an additive, indicating an increase in inter-fibre joint strength. It was also found that a heat treatment of the non-treated papers and of the papers from the PAH treated fibres gave a large improvement in tensile properties as well as Z-strength properties for the different pulps. For the PEC treated fibres it was not necessary to heat-treat the paper to achieve a higher dry strength. The molecular mechanism behind the large improvements is not identified in the present work but the problem is currently being investigated in the lab of the authors.
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53.
  • Gärdlund, Linda, et al. (författare)
  • Influence of polyelectrolyte complexes on the strength properties of papers from unbleached kraft pulps with different yields
  • 2005
  • Ingår i: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 20:1, s. 36-42
  • Tidskriftsartikel (refereegranskat)abstract
    • The properties of the materials combined in corrugated board are set to give the board its strength, flexibility and protection towards impact and pressure. The raw material is of course the single fibre but additives that enhance e.g. the wet and dry paper strength are also added. As the strength enhancing additives used today are most efficient between pH 4 and pH 7 there is a need for new types of additives that can be used under alkaline conditions. In the present report polyallylamine hydrochloride (PAH) and polyelectrolyte complexes (PEC) of PAH and polyacrylic acid (PAA) were investigated as strength enhancing additives. The components can be used under alkaline conditions and results showed that PAH alone or incorporated into a PEC gave different effects regarding strength properties of sheets from kraft pulps of different yields. The results showed that by treating the fibres with PEC's of PAH and PAA it was possible to considerably increase the tensile properties, the Z-strength and the compression strength of papers made from the treated fibres. The results showed an increase of as much as 54 % to 180 % in dry Z-strength and 14 % to 53 % in compression strength, when using the PEC as an additive, indicating an increase in inter-fibre joint strength. It was also found that a heat treatment of the non-treated papers and of the papers from the PAH treated fibres gave a large improvement in tensile properties as well as Z-strength properties for the different pulps. For the PLC treated fibres it was not necessary to heat-treat the paper to achieve a higher dry strength. The molecular mechanism behind the large improvements is not identified in the present work but the problem is currently being investigated in the lab of the authors.
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54.
  • Gärdlund, Linda, et al. (författare)
  • New insights into the structure of polyelectrolyte complexes
  • 2007
  • Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 312:2, s. 237-246
  • Tidskriftsartikel (refereegranskat)abstract
    • The formation of polyelectrolyte complexes (PECs) from oppositely charged linear polyelectrolytes (PELs) was studied using static light scattering at various salt concentrations. The PELs used were poly(allylamine hydro chloride) (PAH) and the two polyanions poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA). Physical characteristics such as the radii of gyration, molecular weights, and water contents of the PECs were determined at various molar mixing ratios. Despite relatively small differences in chemical structure between PAA and PMAA, fairly large differences were detected in these physical characteristics. Generally, PECs comprising PMAA were larger and contained more water. Moreover, by using cryogenic transmission electron microscopy, transmission microscopy and atomic force microscopy, shape and structure of the prepared PECs were investigated both in solution and after drying. The PECs were found to be spherical in solution and the shape was retained after freeze-drying. PECs adsorbed on silica surfaces and dried in air at room-temperature still showed a three-dimensional structure. However, the relatively low aspect ratios indicated that the PECs collapsed significantly due to interactions with the silica during adsorption and drying. At intermediate ionic strengths (1-10 mM), stagnation point adsorption reflectometry (SPAR) showed that the adsorption oflow charged cationic PAH-PAA PECs on silica surfaces increased if the pH value was increased from pH 5.5 to 7.5.
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55.
  • Gärdlund, Linda, 1977- (författare)
  • Polyelectrolyte Complexes : Their Characterization and use for Modification of Wood Fibre Surfaces
  • 2006
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • For economical reasons filler particles and less expensive fibre raw materials are more frequently used in papermaking. This influences the mechanical properties of the formed papers in a negative way and it is therefore necessary to add strength-enhancing agents to the papermaking furnish. Traditionally cationic starch has been the dominating additive used for strength enhancement but new techniques are continuously being developed and in the present work the use of polyelectrolyte complexes (PEC) for improvements of different paper strength properties has been evaluated. Large focus has also been given to evaluating the properties of the polyelectrolyte complexes since these properties are largely dependant on molecular mass of the polyelectrolytes, the mixing conditions and ionic strength of the polyelectrolyte solutions. The PEC formation was studied between chemicals already used for strength enhancing purposes in real papermaking systems, i.e. poly (amido-amine) epichlorohydrin (PAE) and carboxymethylcellulose (CMC). The PEC formation was studied with respect to fundamental characteristics and the ability for use as strength additives. The PEC formation was also studied using model polyelectrolytes (PEL) poly(allylamine hydrochloride) (PAH), as the cationic component, and poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA), as the anionic components. The fundamental studies involve the PEC formation by varying the mixing ratio between the polyelectrolytes, the charge density or molecular weight of a component, structure of the one polyelectrolyte component, the mixing order, together with solution conditions. The main techniques used for these purposes were the static and dynamic light scattering, AFM tapping mode and Cryo-TEM. The adsorption of PECs onto surfaces of silica and lignin was investigated, using the stagnation point adsorption reflectometry (SPAR) and QCM-D (quartz crystal microgravimetry with dissipation). With these two techniques the amount of adsorbed chemical is obtained an also the viscoelastic properties of the adsorbed layer. The stability of PECs towards an increase in salt concentrations was investigated and the PECs were stable up to 0.2-0.4 M NaCl before complete dissolution, suggesting that the driving force for the formation of the PECs (from CMC-PAE) is a combination of the entropic effect of the released counterions and an enthalpy contribution from the interaction between the polymer segments. The PECs did not change their 3D-structure upon drying. It was also found that the swollen 3D structure of the complexes is achieved by an incorporation of a large amount of water into the complexes. Calculations based on the collected results show that the complexes consist of between 60 % and 95 % water. The PECs formed from PAA and PAH displayed higher water content when formed from low PEL concentration and salt concentrations up to 0.1 M NaCl than the PMAA-PAH PECs. At high PEL concentration and high salt concentration the opposite was observed. The use of the complexes as dry strength additives has two large benefits. First of all the 3D structure of the complexes allows for an efficient bridging between the microscopically rough fibre surfaces. Secondly the complexes allows for a higher saturation adsorption of polyelectrolytes on the fibre surface compared with a single polyelectrolyte addition. The PEC addition also leads to an increase in density, but the PECs showed the same benefits as beating when added to the unbeaten fibres. The effect on the fibre material, with regard to paper properties, varies depending on the pulp used.
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56.
  • Gärdlund, Linda, et al. (författare)
  • The use of polyelectrolyte complexes (PEC) as strength additives for different pulps used for production of fine paper
  • 2007
  • Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 22:2, s. 210-216
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work the application of polyelectrolyte complexes (PEC) to different pulps, to improve the strength of papers produced from them, is compared with conventional pulp beating. The pulps chosen for the investigation were a fully bleached chemical hardwood pulp (HBK), a fully bleached chemical softwood pulp (SBK), and a peroxide-bleached chemithermomechanical pulp (BCTMP). The polyelectrolytes used were a polyamideamine epichlorohydrine condensate (PAE), traditionally used as a wet-strength additive, and carboxymethylcellulose. Since the prepared complexes had an anionic charge, they could only be used after fibre pre-treatment with the cationic PAE. Results indicate that the addition of 2% PAE and 2% PEC can improve all the measured tensile strength properties of the sheets as much as is commonly achieved by mechanically beating the pulps. In fact, for the chemical pulps, PEC addition at the chosen level produced better results than did traditional beating, since the improved tensile index and tensile energy absorption could be achieved without any significant deterioration in the light scattering coefficient of the papers produced. However, with the BCTMP a significant decrease in light scattering could be detected, especially following the addition of PEC. Adding the chemicals (especially the PEC) increased the sheet density and this together with the increase in the tensile stiffness, following chemical addition, resulted in a constant bending stiffness of the sheets. However, based on the results it can be suggested that a combination of unbeaten HBK and BCTMP treated with PAE and PEC can be used to produce a strong paper with a high bending stiffness.
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57.
  • Göransson, Nils-Gunnar, et al. (författare)
  • Tillståndsuppföljning av observationssträckor : datainsamling, lägesrapport 2006-12
  • 2007
  • Rapport (populärvet., debatt m.m.)abstract
    • The objective of this project is to collect and deliver high quality road data primarily for development of performance prediction models. The monitoring of LTPP-sections started in 1984 on commission of the Swedish Road Administration. The aim is primarily focused on road deterioration caused by heavy traffic. The project started with a limited amount of sections but the number of sections has increased to 655 sections distributed over 66 sites, still active and inactive, in year 2006. Of budget reasons an overview resulted in a decrease of monitoring sections with 25 %. In the year 2006 there were still 359 active LTPP-sections distributed over 36 sites. Road data from this project has been used for developing models for predicting the cumulative number of load applications to the initiation of cracking for flexible pavements and to develop models for predicting crack propagation in flexible pavements. Crack initiation was defined as the first appearance of cracking in the wheel paths.
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58.
  • Göransson, Nils-Gunnar, et al. (författare)
  • Tillståndsuppföljning av observationssträckor : datainsamling, lägesrapport 2005-12
  • 2006
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • Målsättningen med projektet är att samla in, bearbeta och leverera högkvalitativa data, primärt till utveckling av tillståndsförändringsmodeller. Uppföljningen av observationssträckor (100 meter långa) har, på uppdrag av Vägverket, pågått sedan 1984. Inriktningen är i första hand fokuserad på nedbrytningen som orsakas av tung trafik. De första åren utfördes mätningar på ett begränsat antal sträckor. Antalet har sedan, efterhand som projektet fortskridit, utökats och uppgick vid utgången av år 2005 till 655 stycken fördelade över 66 olika objekt, ingående i det statliga belagda vägnätet. Under årens lopp har antalet bevakade sträckor ändrats så till vida att några utgått och andra tillkommit. En översyn av samtliga sträckor gjordes i början av år 2000. Antalet som fortsättningsvis skulle bevakas, minskades med en fjärdedel. Förändringarna gjordes dock på sådant sätt att högkvalitativa och användbara data fortfarande erhålls från de sträckor som är kvar i uppföljningsprogrammet. Idag är 359 aktiva, fördelade över 36 objekt.
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59.
  • Göransson, Nils-Gunnar, et al. (författare)
  • Tillståndsuppföljning av observationssträckor : Datainsamling, lägesrapport 2004-12
  • 2005
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • Målsättningen med projektet är att samla in, bearbeta och levererahögkvalitativadata, primärt till utveckling av tillståndsförändringsmodeller. Uppföljningenavobservationssträckor (100 meter långa) har, på uppdrag av Vägverket (VV),pågått sedan 1984. Inriktningen är i första hand fokuserad på nedbrytningensomorsakas av tung trafik.
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60.
  • Göransson, Nils-Gunnar, et al. (författare)
  • Tillståndsuppföljning av observationssträckor : datainsamling, lägesrapport 2007-12
  • 2008
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • The objective of this project is to collect and deliver high quality road data primarily for development of performance prediction models. The monitoring of LTPP-sections started in 1984 on commission of the Swedish Road Administration. The aim is primarily focused on road deterioration caused by heavy traffic. The project started with a limited amount of sections but the number of sections has increased to 655 sections distributed over 66 sites, still active and inactive, in year 2007. Of budget reasons an overview resulted in a decrease of monitoring sections with 25 %. In the year 2007 there were still 345 active LTPP-sections distributed over 36 sites. Road data from this project has been used for developing models for predicting the cumulative number of load applications to the initiation of cracking for flexible pavements and to develop models for predicting crack propagation in flexible pavements. Crack initiation was defined as the first appearance of cracking in the wheel paths.
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61.
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62.
  • Horvath, A. Elisabet (författare)
  • The effects of cellulosic fiber charges on polyelectrolyte adsorption and fiber-fiber interactions
  • 2006
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The surface charges of cellulosic fibers contribute to several papermaking operations that influence the manufacture and final properties of paper. This thesis investigates the effect of the surface charges on wet-end chemistry, e.g. through the interaction of cationic polyelectrolytes with the fiber surface charges, and on the network strength of pulp suspensions. The polyelectrolyte titration method was used to investigate the interaction of the fiber charges with cationic polyelectrolytes. Techniques were developed to fluorescent label the adsorbing cationic polyelectrolyte in order to visualize the adsorption behavior. Fluorescent confocal laser scanning microscopy (CLSM) was used to determine the extent to which the cationic polyelectrolyte adsorbs into the porous fiber wall. It was shown that the polyelectrolyte charge density limits the adsorption to the surface under electrolyte-free conditions. Adsorption into the fiber wall only occurs for two conditions: 1) if the molecular mass is sufficiently low or 2) the electrolyte concentration is high enough to screen the charges along the polyelectrolyte backbone but not the interactions between the polyelectrolyte and the fiber charges. Aside from the polyelectrolyte properties, the fiber charge density contributes to the adsorption behavior of cationic polyelectrolytes. The fiber charge profile was altered by bulk and surface carboxymethylation. The electrolyte concentration at which a deviation from 1:1 stoichiometry occurs was shown to be dependent on the amount of surface charges, such that the deviation in stoichiometry occurs at a higher electrolyte concentration for pulps having a higher surface charge. A hypothesis was developed to test the conditions at which the deviation in adsorption stoichiometry occurs, which was defined as the critical electrolyte concentration (CEC). It was found that the CEC corresponded to the electrolyte concentration at which the distance between the fiber charges was on the order of the Debye length. Electron spectroscopy for chemical analysis (ESCA) was used as an independent calibration procedure to validate for which a 1:1 stoichiometry occurs. The analysis with ESCA agreed well with the polyelectrolyte titration method for measurement of fiber surface charges. When measured under appropriate conditions, i.e. electrolyte concentration and molecular properties, the fiber surface charge can accurately be measured by the polyelectrolyte titration method. The charge profiles of various pulp types and treatments were also examined. Having been established as a valid technique, the polyelectrolyte titration method was again used to measure the surface charge while conductometric titration was used to measure the total charge content. The amount of bulk and surface charges vary depending on the pulping method and type of wood, although the ratio between the bulk and surface charge (i.e. the charge ratio) is similar for chemical pulps. The mechanical pulp has a higher charge ratio because it contains more fines material than chemical pulp. Bleaching of the chemical pulp decreases the amount of bulk and surface charges, although the charge ratio remains essentially constant. However, methods such as beating or carboxymethyl cellulose (CMC) grafting are available to increase the charge ratio. The effect of the charge profile on fiber-fiber interactions was studied on both a microscopic and macroscopic level. Colloidal probe microscopy (CPM) was used to investigate the microscopic interactions between two cellulose surfaces. Cellulose surfaces, prepared by spin-coating a dissolving pulp onto silica, were used to model the fiber surface, which is too rough for surface force measurements. The charge density of the model surface was increased by CMC grafting. Results showed that increasing the surface charge density created large electrosteric repulsions, due to CMC the chains protruding out from the surface. These interactions on the microscopic scale affect the fiber network strength, which was measured with a parallel plate rheometer. When the repulsion is increased between the fibers, caused by the increase in the surface charge, fiber flocs break apart more easily due to a reduced friction between the fiber surfaces. The forces acting on the fiber network can also be mechanical in origin. The fiber length and flexibility were altered in order to study the influence of mechanical surface linking and elastic fiber bending on the fiber network strength. Using the storage modulus (G’0) as a measure of fiber network strength, longer fibers were found to create a stronger network due to an increased amount of fiber contacts. Flexible fibers have a lower network strength than stiff fibers because the fibers come to rest in a less strained position such that the the influence of elastic fiber bending on the fiber network strength is predominant.
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63.
  • Horvath, Andrew T., et al. (författare)
  • Adsorption of highly charged polyelectrolytes onto an oppositely charged porous substrate
  • 2008
  • Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 24:15, s. 7857-7866
  • Tidskriftsartikel (refereegranskat)abstract
    • The adsorption behavior of highly charged cationic polyelectrolytes onto porous substrates is electrostatic in nature and has been shown to be highly dependent on the poly electrolyte properties. Copolymers of acrylamide (AM) and diallyldimethylammonium chloride (DADMAC) were synthesized to have a range of macromolecular properties (i.e., charge density and molecular mass). Traditional titration methods have been complemented by fluorescence labeling techniques that were developed to directly observe the extent that fluorescently labeled poly(AM-co-DADMAC) adsorbs into the pore structure of a cellulosic substrate. Although contributing to the electrostatic driving force, the charge density acts to limit adsorption to the outermost surface under electrolyte-free conditions. However, adsorption into the pores can occur if both the molecular mass and charge density of poly(AM-co-DADMAC) are sufficiently low. Adsorption initially increases as the electrolyte concentration is increased. However, the electrostatic persistence length of poly(AM-co-DADMAC) restricts the polyelectrolyte from entering the pores. Therefore, changes in the adsorption behavior at moderate electrolyte concentrations have been attributed to swelling of the polyelectrolyte layer at the fiber exterior. The adsorption behavior changes again at high electrolyte concentrations such that poly(AMco-DADMAC) could adsorb into the pore structure. This occurred when the electrolyte concentration was sufficient to screen the electrostatic persistence length of poly(AM-co-DADMAC), provided that the entropie driving force for adsorption still existed. It is suggested that adsorption into the pore structure is a kinetic process that is governed by localized electrostatic interactions between poly(AM-co-DADMAC) and the charges located within the pores.
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64.
  • Horvath, Andrew T., et al. (författare)
  • Adsorption of low charge density polyelectrolytes to an oppositely charged porous substrate
  • 2008
  • Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 24:13, s. 6585-6594
  • Tidskriftsartikel (refereegranskat)abstract
    • The adsorption behavior of a low charge density cationic polyelectrolyte to cellulosic fibers has been studied. Cationic dextran served as a model polyelectrolyte, as it can be prepared over a range in molecular mass and charge density. The adsorption behavior of the cationic dextran was measured in electrolyte-free conditions using polyelectrolyte titration techniques. By fluorescent labeling the cationic dextran, the extent to which adsorption occurs inside the porous structure was further determined by fluorescent confocal laser scanning microscopy. Cationic dextran having a sufficiently low charge density adsorbed into the pores, although the extent the cationic dextran adsorbed was governed by the molecular mass. The adsorption behavior of the cationic dextran was also studied in various electrolyte concentrations. The adsorbed mass monotonically decreased with increasing electrolyte, as the electrostatic interaction with the substrate was more effectively screened. This behavior also suggests that the interactions between adsorbed polyelectrolyte chains, i.e. lateral correlation effects, are negligible for low charge density polyelectrolytes. Finally, the effect of having a preadsorbed layer of cationic dextran on the adsorption behavior was determined in electrolytefree conditions using fluorescent double staining techniques. The preadsorbed cationic dextran had almost no effect on the adsorption of low molecular mass fractions. Low molecular mass fractions directly adsorbed into the pore structure, as opposed to adsorbing to a free surface and diffusing into the pores. It was also shown that cationic dextran can be selectively adsorbed to different locations, such that the surface of a porous substrate can be treated uniquely from the bulk.
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65.
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66.
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67.
  • Horvath, Andrew T., 1976- (författare)
  • Chemical Methods for Improving the Fracture Toughness of Paper
  • 2008
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Paper is a network material composed of a great number of fibers that interact with each other through fiber joints. In order to make a clear statement regarding observed changes being made in paper, it is vital to determine the structural level of paper that is being affected by chemical modifications. Polyelectrolytes having a wide range in molecular properties have been synthesized to investigate the adsorption behavior of cationic polyelectrolytes to cellulosic fibers. The interaction with the porous cell wall of cellulosic fibers is governed by the molecular properties of the polyelectrolyte. More specifically, polyelectrolytes having a low charge density are able to penetrate into the fiber cell wall, while high charge density polyelectrolytes are restricted to the exterior fiber surface. The molecular mass also influences the extent to which adsorption occurs within the cell wall, although this is typically only pronounced for low charge density polyelectrolytes. High charge density polyelectrolytes are generally restricted to the fiber surface due to strong Coulombic interactions between charged groups along the molecular backbone, which create a stiff molecular conformation. These results were confirmed by fluorescent labeling techniques, which allow the polyelectrolytes to be tracked inside the cell wall by confocal laser scanning microscopy. This approach was also used to demonstrate the effect of an electrolyte, which screens the Coulombic interactions and facilitates penetration into the cell wall. However, a considerable difference in the adsorption behavior of polyelectrolytes having similar molecular mass is still observed at high electrolyte concentration, where the electrostatic contributions are negligible. These differences are a consequence of a diffusion process that occurs on a longer times scale. Although polyelectrolyte adsorption to cellulosic fibers reaches a pseudo-equilibrium at short times, a driving force into the cell wall exists due to the bulk charge of the fiber. The time scale of this diffusion process depends on the polyelectrolyte properties, and was observed to persist for over 3 months. As the extent to which these polyelectrolytes penetrate into the cell wall has been ascertained, and the fibers can be crosslinked to different degrees in the cell wall or at the surface. Cationic acetal dextran was prepared as a model crosslinking agent, as the molecular mass, charge density and degree of acetal substitution can readily be controlled during synthesis. A considerable effect on the tensile properties and fracture toughness was observed for crosslinked paper, which could be attributed to either the fibers or the fiber joints. Crosslinking acted to stiffen the fibers and the fiber joints, which influenced the transfer of applied stresses through the paper structure. Changes in the material behavior at high relative humidity could be improved by crosslinking the fibers at the correct the structural level.
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68.
  • Horvath, Andrew T., et al. (författare)
  • Diffusion of cationic polyelectrolytes into cellulosic fibers
  • 2008
  • Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 24:19, s. 10797-10806
  • Tidskriftsartikel (refereegranskat)abstract
    • The penetration of cationic polyelectrolytes into anionic cellulosic fibers was evaluated with fluorescent imaging techniques in order to clarify the mechanism and time scales for the diffusion process. The bulk charge of the cellulosic fibers indirectly creates a driving force for diffusion into the porous fiber wall, which is entropic in nature due to a release of counterions as the polyelectrolyte adsorbs. The individual bulk charges in the fiber cell wall also interact with the diffusing polyelectrolyte, such that the polyelectrolyte diffuses to the first available charge and consequently adsorbs and remains fixed. Thus, subsequent polyelectrolyte chains must first diffuse through the adsorbed polyelectrolyte layer before adsorbing to the next available bulk charges. This behavior differs from earlier suggested diffusion mechanisms, by which polyelectrolytes were assumed to first adsorb to the outermost surface and then reptate into the pore structure. The time scales for polyelectrolyte diffusion were highly dependent on the flexibility of the chain, which was estimated from calculations of the persistence length. The persistence length ultimately depended on the charge density and electrolyte concentration. The charge density of the polyelectrolyte had a greater influence on the time scales for diffusion. High charge density polyelectrolytes were observed to diffuse on a time scale of months, whereas the diffusion of low charge density polyelectrolytes was measured on the order of hours. An influence of the chain length, that is, steric interactions due the persistence length of the polyelectrolyte and to the tortuosity of the porous structure of the fiber wall, could only be noted for low charge density polyelectrolytes. Increasing the electrolyte concentration increased the chain flexibility by screening the electrostatic contribution to the persistence length, in turn inducing a faster diffusion process. However, a significant change in the diffusion behavior was observed at high electrolyte concentrations, at which the interaction between the polyelectrolyte charges and the fiber charges was almost completely screened.
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69.
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70.
  • Höglund, Anders (författare)
  • Controllable degradation product migration from biomedical polyester-ethers
  • 2007
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The use of degradable biomedical materials has during the past decades indeed modernized medical science, finding applications in e.g. tissue engineering and drug delivery. The key question is to adapt the material with respect to mechanical properties, surface characteristics and degradation profile to suit the specific application. Degradation products are generally considered non-toxic and they are excreted from the human body. However, large amounts of hydroxy acids may induce a pH decrease and a subsequent inflammatory response at the implantation site. In this study, macromolecular design and a combination of cross-linking and adjusted hydrophilicity are utilized as tools to control and tailor degradation rate and subsequent release of degradation products from biomedical polyester-ethers. A series of different homo- and copolymers of -caprolactone (CL) and 1,5-dioxepan-2-one (DXO) were synthesized and their hydrolytic degradation was monitored in phosphate buffer solution at pH 7.4 and 37 °C for up to 546 days. The various materials comprised linear DXO/CL triblock and multiblock copolymers, PCL linear homopolymer and porous structure, and random cross-linked homo- and copolymers of CL/DXO using 2,2’-bis-(ε-caprolactone-4-yl) propane (BCP) as a cross-linking agent. The results showed that macromolecular engineering and controlled hydrophilicity of cross-linked networks were useful implements for customizing the release rate of acidic degradation products in order to prevent the formation of local acidic environments and thereby reduce the risk of inflammatory responses in the body.
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71.
  • Ihs, Anita, et al. (författare)
  • Trafikanters krav på vägars tillstånd : en litteraturstudie rörande trafikantenkäter och trafikintervjuer
  • 2007
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • Today the Swedish Road Administration (SRA) regularly follows up the condition of the state roads by means of road surface measurements. It is mainly rut depth (mm) and roughness expressed in the measure International Roughness Index (IRI, mm/m) that is the bases for assessment of the road surface condition. Based on these measurements it can generally be said that the condition of the roads neither have considerably improved nor become considerably worse over the years. The trend however looks a bit different in the different SRA Regions. At the same time it is also yearly investigated how content or discontent the road users are with the maintenance of the state roads. The road users are asked about their opinion on the operation and maintenance of the roads in general as well as more specifically about their opinion concerning rutting and unevenness, i.e. the factors that are followed up by measurements. The general tendency, except for the last year, is the percentage of satisfied road users is decreasing. The percentage of satisfied road users is also low. This applies not least that the professional drivers. The agreement between the objective measurements of the condition of roads (or rather the condition measures that are used) that are done and the opinions given by the road users is not very good. There is reason to go deeper into this question and examine what requirements and expectations the road users have on the roads/road surface condition and also what measures are needed to describe the condition in a satisfactory way.
  •  
72.
  •  
73.
  • Illergård, Josefin, 1981- (författare)
  • Development of New Bacteria-Reducing Surfaces
  • 2009
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • In recent years, antibacterial surfaces have been a subject of increased interest. Especiallyinteresting are non-leaching, contact-active surfaces that physically disrupts the bacterialcell using immobilised cationic polymers. Thus the risks of bacterial resistance and discharge of hazardous biocides is minimised. The assembly of such surfaces is elaborate andusually involves organic solvents. Here, polyelectrolyte multilayers (PEM) are proposed as an effective surface modification method, with an overall goal of producing antibacterial cellulose fibres. The PEM process is based on physical adsorption of oppositely charged polymers in aqueous solutions. Multilayers were formed with the bactericidal polymer polyvinylamine (PVAm) and polyacrylic acid. PVAm compounds with hydrophobic modificationswere applied as well, as they possess increased antibacterial activity in solution. In this work, the multilayer formation was studied on model surfaces of silicone oxide and glass in order to obtain fundamental knowledge of the polymer system. QCM-D and reflectometry, which detect total mass including bound water and polymer mass only, respectively, were used to analyse the layer formation. Salt-concentrations were varied at 1, 10 or 100 mM NaCl. A stepwise multilayer formation with exponential-like polymer adsorption but with decreasing water content for each layer was seen at all salt concentrations.A higher salt concentration resulted in an increased adsorbed mass. No significant differences in adsorption between the modified and unmodified PVAm could be detected. AFM imaging applied to multilayers having nine layers showed large surface aggregates under high salt conditions for the C6-modified PVAm. Dynamic light scattering showed that the polymer occurred as single molecules in solution; hence it was concluded that theaggregation is surface-associated. The multilayers were then tested for bacterial growth inhibition. The relative bacterial inhibition was time-dependent, as the surface was saturated with bacteria over time. After two hours, a maximal inhibition of 99 % could be observed for the multilayers. After eight hours, a moderate inhibition of less than 40 % was detected. Using multilayers affected the results positively compared to single layers. After three layers, though, no further reductionwas seen. Viability staining of the surface-adhered bacteria revealed that the adhered bacteria had intact membranes. Therefore, the microbiological properties of the multilayers can at this point be described more as growth-inhibiting by bacterial adhesion effectsthan as biocidal. However, this work has shown the importance of combining surface characterisation and microbial testing to understand the bacteria-surface interaction.
  •  
74.
  •  
75.
  • Jacobson, Torbjörn, et al. (författare)
  • Prediction models for pavement wear and associated costs
  • 2005
  • Rapport (populärvet., debatt m.m.)abstract
    • Prediction models that describe changes in the condition of various portions of a road structure constitute a valuable tool for evaluating the service life and economics of a road structure or of a surfacing measure. Prediction models also constitute the core of planning systems - Pavement Management Systems - which are based on changes in the condition of various road structures and asphalt layers depending on traffic and time. The prediction model discussed in this report describes the magnitude of wear of pavement and of rut formation created by vehicles with studded tyres. The objective was to develop a computer based prediction model for the rut formation that is caused by wear from studded tires. The model shall both provide a prediction of the wear resistance of the wearing course based on data regarding the type of wearing course, the properties of component materials, and a model of the rut profile based on data for type of road, traffic load, etc.
  •  
76.
  • Jacobson, Torbjörn, et al. (författare)
  • Utveckling och uppgradering av prognosmodell för beläggningsslitage från dubbade däck samt en kunskapsöversikt över inverkande faktorer : version 3.2.03
  • 2007
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • Prediction models that describe changes in the condition of various portions of a road structure constitute valuable tools for evaluating service life and economics of a road structure or of a surfacing measure. Prediction models also constitute the core of planning systems - Pavement Management Systems - which are based on changes in the condition of various road structures and asphalt layers depending on traffic and time. The prediction model discussed in this report describes the magnitude of wear of pavement and of rut formation created by vehicles with studded tyres. The model is based on the results and experiences gathered during the last twenty years of work at VTI (the Swedish National Road and Transport Research Institute) with the objective of developing and evaluating the wear resistance of asphalt wearing courses. The objective was to develop a computer based prediction model for the rut formation that is caused by wear from studded tires. The model should both provide a prediction of the wear resistance of the wearing course based on data regarding the type of wearing course, the properties of component materials, and a model of the rut profile based on data for type of road, amount traffic, etc. In the first stage, the model was limited to include wearing courses of type ABT (dense-graded asphalt concrete) and ABS (stone matrix asphalt). However, these two types of wearing courses are by far the most common road surfaces on medium to high trafficked roads in Sweden. During the following years the wear model has been validated and calibrated a couple of times. A new updated version of the model was developed during year 2006. In this latest version a few new road types have been added to the model, 2+1 roads and roads with extremely narrow lanes. In the new version it is also possible to use Prall data as input to the model. Prall data is the output from a laboratory wear testing device.
  •  
77.
  • Johansson, Erik, et al. (författare)
  • Adhesive Interaction between Polyelectrolyte Multilayers of Polyallylamine Hydrochloride and Polyacrylic Acid Studied Using Atomic Force Microscopy and Surface Force Apparatus
  • 2009
  • Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 25:5, s. 2887-2894
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
78.
  • Johansson, Erik, et al. (författare)
  • Adsorption Behavior and Adhesive Properties of Biopolyelectrolyte Multilayers formed from Cationic and Anionic Starch
  • 2009
  • Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 10:7, s. 1768-1776
  • Tidskriftsartikel (refereegranskat)abstract
    • Cationic starch (D.S. 0.065) and anionic starch (D.S. 0.037) were used to form biopolyelectrolyte multilayers. The influence of the solution concentration of NaCl on the adsorption of starch onto silicon oxide substrates and on the formation of multilayers was investigated using stagnation point adsorption reflectometry (SPAR) and quartz crystal microbalance with dissipation (QCM-D). The wet adhesive properties of the starch multilayers were examined by measuring pull-off forces with the AFM colloidal probe technique. It was shown that polyelectrolyte multilayers (PEM) can be successfully constructed from cationic starch and anionic starch at electrolyte concentrations of 1 mM NaCl and 10 mM NaCl. The water content of the PEMs was approximately 80% at both electrolyte concentrations. However, the thickness of the PEMs formed at 10 mM NaCl was approximately twice the thickness formed at I mM NaCl. The viscoelastic properties of the starch PEMs, modeled as Voigt elements, were dependent on the polyelectrolyte that was adsorbed in the outermost layer. The PEMs appeared to be more rigid when capped by anionic starch than when capped by cationic starch. The wet adhesive pull-off forces increased with layer number and were also dependent oil the polyelectrolyte adsorbed in the outermost layer. Thus, starch PEM treatment has a large potential for increasing the adhesive interaction between solid substrates to levels higher than can be reached by a single layer of cationic starch.
  •  
79.
  • Josefsson, Peter (författare)
  • Biochemical modification of wood components
  • 2006
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The degradation of cellulose found in wood is one of the most important degradation processes for the carbon flux on earth. The degradation is performed by microorganisms that typically use enzymes. Since the cellulose in wood is crystalline and embedded in other polymers, making it inaccessible and durable, the enzymatic methods of cellulose degradation is also complex. In this thesis, the action of some of these enzymes, called cellulases, have been studied both fundamentally and for industrial purposes. By using model cellulose films and a quartz crystal microbalance it was found that endoglucanases not only depolymerize but also swell model cellulose films. Most probably, this contributes to the synergy seen between endoglucanases and exoglucanases. When an pulp fibers were pre--treated with endoglucanases and beaten subsequently, the fibers became more swollen than reference fibers. The effects of beating enzyme pre--treated fibers were investigated, indicating that endoglucanases improves the fiber/fiber interaction but also alters the behavior of the fibers in the beating process to become more susceptible to the beating. The second part of the thesis has been focused on the use of an albino fungi in order to decrease the amount of wood extractives in wood chips prior to thermo mechanical pulp production. The fungus decreased the most troublesome component, the triglycerides, by more than 90 percent in two weeks without any detrimental effects on pulp properties. On the contrary, pulp strength and optical properties were improved.
  •  
80.
  •  
81.
  • Josefsson, Peter, et al. (författare)
  • The physical action of cellulases revealed by a quartz crystal microbalance study using ultrathin cellulose films and pure
  • 2008
  • Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 9:1, s. 249-254
  • Tidskriftsartikel (refereegranskat)abstract
    • The effects of fungal cellulases on model cellulose films were studied using a high-resolution quartz crystal microbalance (QCM) sensitive to minute changes of the nanometer thick model cellulose films. It was found that endoglucanases not only produce new end groups but also cause a swelling of the cellulose film. The cellobiohydrolases degraded the films quickly, which was detected as a rapid decrease in the remaining amount of cellulose on the QCM crystal. However, changing viscoelastic properties of the films also indicated a softening of the film during the degradation. A defined mixture of selected cellulases caused a significantly higher rate of degradation than only cellobiohydrolases. Cellulase synergism is discussed with the endoglucanase swelling effects and film softening added.
  •  
82.
  • Larsson, Per A., et al. (författare)
  • A novel approach to study the hydroexpansion mechanisms of paper using spray technique
  • 2009
  • Ingår i: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 24:4, s. 371-380
  • Tidskriftsartikel (refereegranskat)abstract
    • A new method has been developed to measure the dimensional stability of printing paper by measuring the impact of liquid water on the in-plane dimensional change, i.e. the hydroexpansion, without any simultaneous mechanical interference that can occur when water is pressed into the sheet. This was achieved by using a specially developed spray technique and using electronic speckle photography to continuously measure the dimensional change as water is applied. The in-plane expansion for a given change in moisture content was found to be lower in the case of hydroexpansion than for earlier reported hygroexpansion. After the initial expansion following the water application, it was found that sheets rapidly start to contract again already 10-20 seconds after being wetted, i.e. despite still having a fairly constant and significantly higher moisture content than the initial moisture content before water application. These effects suggest that there are different mechanisms behind hydroexpansion than hygroexpansion of paper, and that hygroexpansion measurements should be extrapolated with caution when evaluating papers with respect to printability.
  •  
83.
  • Larsson, Per A., 1980-, et al. (författare)
  • Influence of fibre-fibre joint properties on the dimensional stability of paper
  • 2008
  • Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 15:4, s. 515-525
  • Tidskriftsartikel (refereegranskat)abstract
    • Measurements have been performed to clarify the connection between fibre-fibre joint properties and dimensional stability using laboratory sheets prepared from never-dried fibres, from heavily hornified fibres having a low molecular contact area between the fibres, and from both hornified and never-dried fibres treated with a polyelectrolyte multilayer (PEM) technique to increase the molecular contact area in the fibre-fibre joint. The influence of the drying mode, i.e. whether the sheets are dried freely or under restraint, was also evaluated. The results showed that neither paper strength nor fibre-fibre joint contact area had any significant influence on the dimensional stability of sheets dried under restraint. On the other hand, when the sheets were dried freely, the PEM-treated sheets expanded to the same extent as, or to an even greater extent than the non-PEM-treated sheets, even though they adsorbed less water for a given change in relative humidity. There was also a correlation between drying shrinkage and dimensional stability, where greater shrinkage was associated with a greater hygroexpansion in the freely dried sheets.
  •  
84.
  • Larsson, Per A., et al. (författare)
  • The Influence Of Grammage, Moisture Content, Fibre Furnish And Chemical Modifications On The Hygro- And Hydro-Expansion Of Paper
  • 2009
  • Ingår i: ADVANCES IN PULP AND PAPER RESEARCH, OXFORD 2009, VOLS 1-3. - 9780954527266 ; , s. 355-388
  • Konferensbidrag (refereegranskat)abstract
    • The conventional way to evaluate dimensional stability, regardless of end-use purpose, is to measure the change in dimensions when the moisture content is changed by changing the relative humidity. Sorption of moisture from moist air is a relatively slow process and for the evaluation of printing papers this may not be the most appropriate method. In the present work, data from conventional hygroexpansion measurements has been compared with data from hydroexpansion measurements, i.e. expansions caused by the sorption of liquid water, sprayed onto papers printed with a random speckle pattern, the expansion being monitored by electronic speckle photography. Sheets made from different pulps, with different fines contents and different modifications were studied at different grammages and water-transfer levels. The effect of drying-mode, i.e. restrained drying or free drying, was also studied. It was concluded that sheets expand less with a given amount of adsorbed water when it is sorbed in liquid form rather than from moist air. Chemical treatments known to increase both the dry and the wet strength, e.g. polyelectrolyte multilayers and cross-linking through periodate oxidation, did not significantly improve the dimensional stability when the papers were exposed to liquid water.
  •  
85.
  • Larsson, Per A., et al. (författare)
  • The influence of periodate oxidation on the moisture sorptivity and dimensional stability of paper
  • 2008
  • Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 15:6, s. 837-847
  • Tidskriftsartikel (refereegranskat)abstract
    • The hygroexpansion of paper was significantly reduced, up to 28% lower amplitude of change when the paper was subjected to a change in relative humidity from 20 to 85% RH, by oxidation of the fibre wall. Never-dried bleached kraft fibres were oxidised with sodium periodate, which specifically oxidises the C2-C3 bond of 1,4-glucans so that the cellulose is partly converted into dialdehyde cellulose. Since both the dry and wet strength of laboratory sheets were significantly improved, the dry tensile strength increased from 24 kNm/kg up to 66 kNm/kg and the relative wet tensile strength increased from 1.5% up to 40%, it is suggested that the aldehydes form hemiacetal linkages within the fibre wall during the consolidation and drying of the sheets. The mechanical, hygroexpansive and moisture sorptive properties of the sheets made from the oxidised fibres were studied. The results showed that the main reason for the reduced hygroexpansion was a decrease in moisture sorptivity, i.e. when the sheets made of fibres with different degrees of cross-linking were subjected to the same change in relative humidity, the more cross-linked fibres showed a smaller change in moisture content. It was also shown that the hygroexpansion coefficient, i.e. the moisture-normalised dimensional change, was not significantly changed by the periodate oxidation, i.e. indicating that there are no improvement in dimensional stability if the paper is subjected to a specific amount of water.
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86.
  • Lingström, Rikard, 1978- (författare)
  • Formation and properties of polyelectrolyte multilayers on wood fibres : influence on paper strength and fibre wettability
  • 2006
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • 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.
  •  
87.
  • Lingström, Rikard, et al. (författare)
  • Formation of polyelectrolyte multilayers on fibres : Influence on wettability and fibre/fibre interaction
  • 2006
  • Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 296:2, s. 396-408
  • Tidskriftsartikel (refereegranskat)abstract
    • 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).
  •  
88.
  • Lingström, Rikard, 1978- (författare)
  • On the Adhesion Between Substrates Covered with Polyelectrolyte Multilayers
  • 2008
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • 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.
  •  
89.
  • Lingström, Rikard, et al. (författare)
  • Polyelectrolyte Multilayers for Fibre Engineering
  • 2009
  • Ingår i: The Nanoscience and Technology of Renewable Biomaterials. - Chichester, UK : John Wiley & Sons. - 9781405167864 ; , s. 123-148
  • Bokkapitel (refereegranskat)
  •  
90.
  • Lingström, Rikard, et al. (författare)
  • Polyelectrolyte multilayers on wood fibers : Influence of molecular weight on layer properties and mechanical properties of papers from treated fibers
  • 2008
  • Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 328:2, s. 233-242
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
91.
  • Lingström, Rikard, et al. (författare)
  • Wettability changes in the formation of polymeric multilayers on cellulose fibres and their influence on wet adhesion
  • 2007
  • Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 314:1, s. 1-9
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
  •  
92.
  • Lundström-Hämälä, Lisa, et al. (författare)
  • The adsorption of polyelectrolyte multilayers (PEM) of starch on mechanical pulps for improved mechanical paper properties
  • 2009
  • Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 24:4, s. 459-468
  • Tidskriftsartikel (refereegranskat)abstract
    • In the present work, the long fibre and middle fibre fraction of a thermomechanical pulp (TMP) was treated with polyelectrolyte multilayers (PEMs) of cationic and anionic starch and sheets were made from both the treated and untreated fractions. In separate experiments, different amounts of untreated fines were added to the PEM-treated fraction before sheets were prepared, and the results were also compared with PEM treatment of the entire pulp containing 17% fines before sheet preparation. The PEMs were made of two different combinations of starch, two cationic potato starches with DS values of 0.06 and 0.09, both in combination with an anionic potato starch with a DS of 0.04, at 0.010 M NaCl and pH 6.3. Sheets were formed using the Rapid Kothen sheet former and the resulting mechanical and optical sheet properties were evaluated. Four-layer PEM treatment of the long fibre and middle fraction resulted in significant improvements in in-plane and out-of-plane mechanical properties. However, a subsequent fines addition reduced the effect of the PEMs, and this is explained by a blocking of the necessary PEM interaction with the treated TMP long fibre and middle fraction by the subsequently added fines. PEM treatment of the entire pulp increased the amount of starch needed for PEM treatment, but improved the in-plane and out-of-plane mechanical properties compared with those of sheets prepared from a PEM-treated long fibre and middle fraction with a subsequent addition of fine material. The increase in the tensile index for sheets made from a PEM-treated long fibre and the middle fraction without a subsequent fines addition, however, was much larger.
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93.
  • Lundström, Lisa (författare)
  • Polyelectrolyte multilayers of cationic and anionic starch and their use for improving the strength of papers made from mechanical pulps
  • 2009
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Graphic paper is experiencing severe competition from other materials and, most of all, from other media. This means there is a great need to improve paper quality while reducing raw material and production costs. Polyelectrolyte multilayer (PEM) treatment (i.e., consecutively adding cationic and anionic polyelectrolytes to the charged surface of wood fibres and fines, to form layers of these polyelectrolytes on the fibres/fines) has in recent years been found to offer great potential both to introduce new properties and to improve the mechanical properties of papers made of the treated fibres. The main objective of this thesis was to develop a strategy for the PEM treatment of cationic and anionic starch to improve the mechanical properties of paper made of thermomechanical pulp (TMP), since PEM treatment of fibres has displayed great potential to improve the mechanical properties of sheets made of chemical pulp. Mechanical pulp, however, has a large fine material content. Since the fine material is highly charged, polyelectrolyte consumption would be unacceptably high if the entire pulp were PEM treated, so we applied PEM treatment only to a fibre fraction of the pulps in most trials in the present work. The polyelectrolytes used for PEMs have so far mostly been well-defined, expensive ones unsuitable for use in standard paper grades; to develop a more economically realistic alternative, we used cationic and anionic starches. PEM formation on SiO2 surfaces from three differently charged cationic and anionic starches was first evaluated at three different salt levels using quartz crystal microbalance with dissipation (QCM-D) and stagnation point adsorption reflectometry (SPAR). The starch combinations displaying the highest potential for stable PEM formation at higher salt concentrations were then evaluated on an entire TMP pulp, as well as on a fraction of the pulp to reduce the amount of starch needed for PEM formation. The results indicate that it is possible to form PEMs from cationic and anionic starch on a SiO2 surface. The charge density, salt concentration, and combination of starches all influenced PEM formation. PEM formation on mechanical fibres produced large improvements in the mechanical properties of the sheets made of the treated fibres, and the tensile index, stretch-at-break, Z-strength, and Scott bond values all increased. Fractionating the pulp and PEM treating only a fraction of the pulp, the long fibre and middle fraction, produced large decreases in the amount of starch needed and large improvements in the mechanical properties of the sheets when no fine material was subsequently added. As untreated fine material was subsequently added, the improvement in mechanical properties decreased. PEM formation produced almost no reduction in formation and only a slight increase in sheet density.
  •  
94.
  •  
95.
  • Nilsson, Jan-Eric, et al. (författare)
  • Funktionsupphandling : sammanfattning av kunskapsläge och rekommendationer för fortsatt forskning
  • 2006
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • The Swedish concept "procurement of function" corresponds to performance contracting in Anglo-Saxon countries. The substance is that principal and agent signs a contract over the construction and maintenance of a specific project based on the services provided to future users, i.e. based on performance of the asset. This is in contrast with contracting base on technical qualities of the new road. VTI has reserved funds to provide an overview of current knowledge in this context. Four separate contributions, together with a short summary, are included in this report. One conclusion is that the experiences of this contractual form are much larger in other countries than in Sweden. We therefore have a lot to learn, not least from our closest neighbours Finland and Norway. International experiences indicate a large and growing interest in this form of contracting and provides reason for further development. A second conclusion is that Sweden in general and VTI in particular has important information of direct relevance for the development of efficient performance contracts. This knowledge must, however, typically be structured and organised along other lines than when the original research was undertaken. The institute should therefore seek to adapt the collection of information of relevance for performance contracts so that it fits in to this new framework. This includes issues such as the measurement of road surface quality and assessment of the additional costs for providing better surface quality on the one hand and the user benefits of improved quality on the other.
  •  
96.
  •  
97.
  • Norgren, Magnus, et al. (författare)
  • Smooth model surfaces from lignin derivatives. II. Adsorption of polyelectrolytes and PECs monitored by QCM-D
  • 2007
  • Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 23:7, s. 3737-3743
  • Tidskriftsartikel (refereegranskat)abstract
    • For the first time to the knowledge of the authors, well-defined and stable lignin model surfaces have been utilized as substrates in polyelectrolyte adsorption studies. The adsorption of polyallylamine (PAH), poly(acrylic acid) (PAA), and polyelectrolyte complexes (PECs) was monitored using quartz crystal microgravimetry with dissipation (QCM-D). The PECs were prepared by mixing PAH and PAA at different ratios and sequences, creating both cationic and anionic PECs with different charge levels. The adsorption experiments were performed in 1 and 10 mM sodium chloride solutions at pH 5 and 7.5. The highest adsorption of PAH and cationic PECs was found at pH 7.5, where the slightly negatively charged nature of the lignin substrate is more pronounced, governing electrostatic attraction of oppositely charged polymeric substances. An increase in the adsorption was further found when the electrolyte concentration was increased. In comparison, both PAA and the anionic PEC showed remarkably high adsorption to the lignin model film. The adsorption of PAA was further studied on silica and was found to be relatively low even at high electrolyte concentrations. This indicated that the high PAA adsorption on the lignin films was not induced by a decreased solubility of the anionic polyelectrolyte. The high levels of adsorption on lignin model surfaces found both for PAA and the anionic PAA-PAH polyelectrolyte complex points to the presence of strong nonionic interactions in these systems.
  •  
98.
  • Notley, S. M., et al. (författare)
  • Morphology of modified regenerated model cellulose II surfaces studied by atomic force microscopy : Effect of carboxymethylation and heat treatment
  • 2005
  • Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 6:3, s. 1586-1591
  • Tidskriftsartikel (refereegranskat)abstract
    • Model cellulose II surfaces with different surface charge have been prepared from carboxymethylated wood pulp. AFM tapping-mode imaging in air showed that the introduction of charged groups into the film does not appreciably change the surface morphology. However, after a mild heat treatment (heating at 105 ° C for 6 h), an irreversible surface structure change, from near spherical-type aggregates to a fibrillar structure, was observed. This might be attributed to the formation of strong hydrogen bonds in the crystalline region of the films while the amorphous regions shrank upon drying. The suitability of these charged cellulose films for surface forces studies was also investigated. At pH below the pK(a) of the carboxyl groups present in the film, the interaction force could be fit by a van der Waals force interaction. At higher pH, the interaction was of a purely electrostatic nature with no van der Waals component observable due to the swelling of the surfaces.
  •  
99.
  • Notley, S.M., et al. (författare)
  • Surface Forces Measurements of Spin-Coated Cellulose Thin Films with Different Crystallinity
  • 2006
  • Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 22:7, s. 3154-3160
  • Tidskriftsartikel (refereegranskat)abstract
    • A systematic study of the surface forces between a cellulose sphere and cellulose thin films of varying crystallinity has been conducted as a function of ionic strength and pH. Semicrystalline cellulose II surfaces and amorphous cellulose films were prepared by spin-coating of the precursor cellulose solutions onto oxidized silicon wafers before regeneration in water. Crystalline cellulose I surfaces were prepared by spin-coating wafers with aqueous suspensions of sulfate-stabilized cellulose I nanocrystals. These preparation methods produced thin, smooth films suitable for surface forces measurements. The interaction with the cellulose I was monotonically repulsive at pH 3.5, 5.8, and 8.5 and at 0.1, 1, and 10 mM ionic strengths. This was attributed to the presence of strongly ionizable sulfur-containing groups on the cellulose nanocrystal surfaces. The amorphous film typically showed a steric interaction up to 100 nm away from the interface that was independent of the solution conditions. A range of surface forces were successfully measured on the semicrystalline cellulose II films; attractive and repulsive regimes were observed, depending on pH and ionic strength, and were interpreted in terms of van der Waals and electrostatic interactions. Clearly, the forces acting near cellulose surfaces are very dependent on the way the cellulose surface has been prepared.
  •  
100.
  • Notley, Shannon, et al. (författare)
  • Visco-elastic and adhesive properties of adsorbed polyelectrolyte multilayers determined in situ with QCM-D and AFM measurements
  • 2005
  • Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 292:1, s. 29-37
  • Tidskriftsartikel (refereegranskat)abstract
    •  The build-up of multilayers constructed from polyallylamine hydrochloride (PAH) and polyacrylic acid (PAA) under different pH conditions was continuously monitored using the quartz crystal microbalance with dissipation. The adsorbed amount of polymer as well as the amount of coupled water was determined. Furthermore, from dissipation measurements, it was possible to determine the visco-elastic properties of the adsorbed multilayer. These properties were highly dependent on the polyelectrolyte present in the outermost layer. The multilayer was far more rigid and elastic with PAA as the outermost layer. Furthermore, a link has been established between the conformability or rigidity of a multilayer covered surface and the adhesion between such surfaces. Adhesion measurements Using the atomic force microscope showed a greater pull-off force when the more viscous PAH was present in the outermost layer.
  •  
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