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Chemical Methods for Improving the Fracture Toughness of Paper
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

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.

Place, publisher, year, edition, pages
Stockholm: KTH , 2008. , 112 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2008:28
Keyword [en]
chemistry, physical chemistry
National Category
Paper, Pulp and Fiber Technology
Identifiers
URN: urn:nbn:se:kth:diva-4752ISBN: 978-91-7178-968-6 (print)OAI: oai:DiVA.org:kth-4752DiVA: diva2:13781
Public defence
2008-05-30, F3, KTH, Lindstedtsvägen 26, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100811Available from: 2008-05-15 Created: 2008-05-15 Last updated: 2010-08-11Bibliographically approved
List of papers
1. Influence of polymeric additives on short-time creep of paper
Open this publication in new window or tab >>Influence of polymeric additives on short-time creep of paper
2007 (English)In: Nordic Pulp and Paper Research Journal, ISSN 0283-2631, Vol. 22, no 2, 217-227 p.Article in journal (Refereed) Published
Abstract [en]

Cationic polyallylamine (PAH) and cationic starch were adsorbed to unbleached softwood kraft pulp fibres in order to study the effect of these additives on the creep properties of the resulting paper sheets. For the fibres treated with PAH, the effect of molecular mass, adsorbed quantity and heat treatment of the prepared sheets at 160 degrees C was also studied. PAH was found to not influence the sheet density, whereas starch addition induced moderate densification. Both additives produced major improvements in dry strength measurements as stress and strain-at-break. PAH-treated sheets also showed a relatively small but statistically significant improvement in tensile stiffness, unlike starch-treated sheets in which the improvement was too small to be statistically significant. As expected. there was an inverse relationship between the adsorbed amount and the molecular mass of the PAH. However, for comparable adsorbed amounts, the molecular mass made no detectable difference to the mechanical properties. PAH was also labelled with fluorescein isothiocyanate and adsorbed to the pulp fibres. Examination of the fibres with a confocal scanning laser microscope revealed that the different molecular mass fractions adsorbed only to the exterior parts of the fibres (i.e. the molecules did not penetrate throughout the fibre wall). The creep behaviour of the paper sheets was evaluated under tensile loading using a specially designed testing apparatus, in both 50% RH and 90% RH at 23 degrees C. Strain was monitored as function of time and applied load. PAH was found to lower both instantaneous and time-dependent deformation during the relatively short measuring time of 100 seconds used in this work. Cationic starch had little or no effect on creep. Thus it is clearly demonstrated that PAH treatment of fibres results in sheets with a lower creeping tendency over short periods compared to sheets made with non-treated and starch-treated fibres.

Keyword
creep; mechanical properties; polyallylamine; cationic starch; confocal fluorescence microscopy
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-7717 (URN)10.3183/NPPRJ-2007-22-02-p217-227 (DOI)000248057800011 ()2-s2.0-34547345846 (Scopus ID)
Note
QC 20100616Available from: 2007-11-25 Created: 2007-11-25 Last updated: 2010-08-11Bibliographically approved
2. Adsorption of Highly Charged Polyelectrolytes onto an Oppositely Charged Porous Substrate
Open this publication in new window or tab >>Adsorption of Highly Charged Polyelectrolytes onto an Oppositely Charged Porous Substrate
2008 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, no 15, 7857-7866 p.Article in journal (Refereed) Published
Abstract [en]

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 polyelectrolyte 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 call 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 ill 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(AM-co-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 entropic 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.

Keyword
Amides; Amplitude modulation; Charge density; Concentration (process); Electrolysis; Electrolytes; Electrostatics; Fees and charges; Fiber optics; Finance; Hydrogels; Labeling; Molecular mass; Polyelectrolytes; Polymers; Pore structure; Substrates; Surface charge; Titration; Volumetric analysis; Acrylamide; Adsorption behavior; Cationic polyelectrolytes; Charged polyelectrolytes; Diallyldimethylammonium chloride; Driving forces; Electrolyte concentrations; Electrolyte properties; Electrostatic driving; Electrostatic interactions; Fluorescence labeling; Kinetic processes; Persistence lengths; Porous substrates
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-8451 (URN)10.1021/la800093m (DOI)000258034500034 ()2-s2.0-49649115957 (Scopus ID)
Note
QC 20100811. Uppdaterad från accepted till published (20100811).Available from: 2008-05-15 Created: 2008-05-15 Last updated: 2010-08-11Bibliographically approved
3. Adsorption of Low Charge Density Polyelectrolytes to an Oppositely Charged Porous Substrate
Open this publication in new window or tab >>Adsorption of Low Charge Density Polyelectrolytes to an Oppositely Charged Porous Substrate
2008 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, no 13, 6585-6594 p.Article in journal (Refereed) Published
Abstract [en]

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 electrolyte-free 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.

Keyword
Adsorption; Charge density; Confocal microscopy; Electrolysis; Electrolytes; Flow interactions; Fluorescence; Glucose; Imaging techniques; Labeling; Light emission; Luminescence; Molecular mass; Painting; Polyelectrolytes; Polymers; Pore structure; Pulsed laser deposition; Substrates; Theorem proving; Volumetric analysis; Adsorption behavior; American Chemical Society (ACS); Cationic polyelectrolytes; Cellulosic fibers; Confocal laser scanning micro scopy (CLSM); Electrolyte concentrations; Electrostatic interactions; Fluorescent labeling; Free surfaces; Lateral correlation; Low charge density polyelectrolytes; Low molecular mass (LMM); Monotonically; Polyelectrolyte chains; Porous structures; Porous substrates; Staining techniques
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-8452 (URN)10.1021/la800274w (DOI)000257101100029 ()2-s2.0-47349132325 (Scopus ID)
Note
QC 20100811. Uppdaterad från accepted till published (20100811).Available from: 2008-05-15 Created: 2008-05-15 Last updated: 2010-08-11Bibliographically approved
4. Polyelectrolyte Diffusion Into an Oppositely Charged Porous Substrate
Open this publication in new window or tab >>Polyelectrolyte Diffusion Into an Oppositely Charged Porous Substrate
2008 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827Article in journal (Refereed) Accepted
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-8453 (URN)
Note
QC 20100811Available from: 2008-05-15 Created: 2008-05-15 Last updated: 2010-08-11Bibliographically approved
5. Effect of Cross-Linking Fiber Joints on the Tensile and Fracture Behavior of Paper
Open this publication in new window or tab >>Effect of Cross-Linking Fiber Joints on the Tensile and Fracture Behavior of Paper
2010 (English)In: Industrial & Engineering Chemistry Research, ISSN 0888-5885, Vol. 49, no 14, 6422-6431 p.Article in journal (Refereed) Published
Abstract [en]

The tensile and fracture properties of cross-linked paper were investigated at low and high relative humidity by cross-linking the joints formed between fibers. Cationic acetal dextran served as a model cross-linking agent, as it can be prepared to adsorb specifically to the fiber surface. Thus, cross-linking occurs only in the joints between fibers. The kinetics of hydrolysis was investigated to optimize the stock preparation, such that the resulting aldehyde groups react as the paper is dried. The effect of the cross-link density on the tensile and fracture properties was studied by varying the amount of acetal groups adsorbed to the pulp fibers. At low humidity, cross-linking improved the tensile and fracture properties of paper, although lower cross-link densities yielded better properties. Cross-linking was not effective at high relative humidty, as the tensile strength and stiffness were not improved. However, the fracture properties were significantly improved.

Keyword
DRY STRENGTH, CATIONIC POLYACRYLAMIDES, HARDENING MATERIAL, ADSORPTION, POLYMERS, DEXTRAN, CRACK
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-8454 (URN)10.1021/ie100334z (DOI)000279747000022 ()2-s2.0-79952475159 (Scopus ID)
Note

QC 20100811. Uppdaterad från manuskript till artikel (20100811). Tidigare titel: Effect of Crosslinking Fiber Joints on the Tensile and Fracture Behavior of Paper

Available from: 2008-05-15 Created: 2008-05-15 Last updated: 2015-05-26Bibliographically approved
6. Influence of Crosslinking the Fiber Cell Wall on the Tensile and Fracture Properties of Paper
Open this publication in new window or tab >>Influence of Crosslinking the Fiber Cell Wall on the Tensile and Fracture Properties of Paper
(English)Manuscript (Other academic)
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-8455 (URN)
Note
QC 20100811Available from: 2008-05-15 Created: 2008-05-15 Last updated: 2010-08-11Bibliographically approved

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Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
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  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
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Output format
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  • asciidoc
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