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The Influence of Molecular Adhesion on Paper Strength
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis deals with the influence of molecular adhesion on paper strength. By combining the use of high-resolution techniques and silica/cellulose surfaces, with various fibre–fibre and sheet testing techniques, new information regarding the molecular mechanisms responsible for paper strength has been obtained.

Large parts of this research were devoted to the polyelectrolyte multilayer (PEM) technique, i.e. a charged surface is consecutively treated with oppositely charged polyelectrolytes. Application of PEMs incorporating polyallylamine hydrochloride (PAH) and polyacrylic acid (PAA) onto dried, fully bleached softwood fibres, prior to sheet preparation, increased tensile strength. No linear relationship was detected between the amounts of PAH and PAA adsorbed onto the fibres and the developed tensile strength, which suggests that the adsorbed amount is not the only important factor determining the tensile strength. Closer examination of PEM formation on silica indicated that both exponential PEM film growth and the occurrence of a PEM film in which the polyelectrolytes are highly mobile, favour the strength-enhancing properties of sheets containing PEM-treated fibres. This indicates that a water-rich, soft PEM film allows the polyelectrolytes to diffuse into each other, creating a stronger fibre–fibre joint during consolidation, pressing, and drying of the paper. In addition, when PAH capped the PEM film, the paper strength was higher than when PAA capped the film; this could be related to the structure of the adsorbed layer. Further analysis of the sheets revealed that the increase in tensile strength can also be linked to an increase in the degree of contact within a fibre–fibre joint, the number of efficient joints, and the formation of covalent bonds. The relative bonded area (RBA) in the sheets, as determined using light-scattering measurements, indicated no significant change until a certain tensile strength was obtained. The RBA, as determined using nitrogen adsorption via BET analysis, did show significant changes over the whole investigated tensile strength range. From this it can be concluded that light scattering cannot give any direct information regarding molecular interactions within a sheet. Furthermore, it was shown that PEMs involving cationic and anionic starch display an almost linear relationship with out-of-plane strength properties regarding the amount of starch in the sheets, whereas the tensile strength was more dependent on the physical properties of the starch, as was the case with PAH and PAA.

Cationic dextran (DEX) and hydrophobically modified cationic dextran (HDEX) were used to test the importance of having compatible surface layers in order to obtain strong adhesive joints. DEX and HDEX phase separated in solution, however, this incompatibility of HDEX:DEX mixtures was not reflected in wet or dry joint strength. For both wet and dry measurements, adhesion between DEX and HDEX coated surfaces was intermediate to the adhesion of DEX:DEX and HDEX:HDEX surfaces.

In addition, various types of cellulose surfaces, different regarding their crystallinity, were investigated. Depending on the preparation techniques and solution conditions used, i.e. pH and salt concentration, steric, electrostatic, and van der Waals interactions were obtained between the surfaces in aqueous solutions. The adhesion forces between polydimethylsiloxane and cellulose surfaces, measured under ambient conditions, were influenced by the degree of crystallinity. This suggests that amorphous cellulose offers more possibilities for surface groups to arrange themselves to participate in molecular interactions in the joint. Higher relative humidity could increase this adhesion force further, water probably acting as a plasticizer during joint formation.

Place, publisher, year, edition, pages
Stockholm: KTH , 2006. , 81 p.
Series
Trita-FPT-Report, ISSN 1652-2443 ; 2006:25
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-4101OAI: oai:DiVA.org:kth-4101DiVA: diva2:10742
Public defence
2006-09-30, F3, Lindstedtsvägen 26, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20110125Available from: 2006-09-14 Created: 2006-09-14 Last updated: 2011-01-25Bibliographically approved
List of papers
1. The influence on paper strength properties when building multilayers of weak polyelectrolytes onto wood fibres
Open this publication in new window or tab >>The influence on paper strength properties when building multilayers of weak polyelectrolytes onto wood fibres
2005 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 292, no 1, 38-45 p.Article in journal (Refereed) Published
Abstract [en]

Polyallylamine hydrochloride (PAH) and polyacrylic acid (PAA) have been used to build up polyelectrolyte multilayers (PEM) on wood fibres and on silicon oxide surfaces, under various pH conditions. Consecutive adsorption onto silicon oxide surfaces of PAH and PAA were studied using stagnation point adsorption reflectometry, and the results showed a steady build-up of multilayers. Furthermore, by altering pH, the build-up of the multilayer could be made either linear or exponential in terms of adsorbed amount. Nitrogen analysis of sheets prepared from modified fibres showed that the adsorbed amount of PAH increased throughout PEM build-up, the amount of increase depending on pH during adsorption. Strength measurements of the sheets, i.e., stress at break and strain at break, showed significant improvements ranging from 60 to 200%, depending on both pH during adsorption and type of polyelectrolyte in the outer layer. A good correlation between the adsorbed amount of PAH and the improved strength properties of the paper was also found.

Keyword
Adsorption, Fibre bonding, Multilayer, Optical reflectometry, Paper strength, Polyelectrolyte, Refractive index increment, Strain at break, Tensile index
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-6116 (URN)10.1016/j.jcis.2005.05.058 (DOI)000233175700005 ()2-s2.0-27444444504 (Scopus ID)
Note

QC 20101001

Available from: 2006-09-14 Created: 2006-09-14 Last updated: 2012-10-02Bibliographically approved
2. Visco-elastic and adhesive properties of adsorbed polyelectrolyte multilayers determined in situ with QCM-D and AFM measurements
Open this publication in new window or tab >>Visco-elastic and adhesive properties of adsorbed polyelectrolyte multilayers determined in situ with QCM-D and AFM measurements
2005 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 292, no 1, 29-37 p.Article in journal (Refereed) Published
Abstract [en]

 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.

Keyword
polyelectrolyte, multilayer, quartz crystal microbalance with dissipation, atomic force microscope, adhesion, visco-elastic properties
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-6117 (URN)10.1016/j.jcis.2005.05.057 (DOI)000233175700004 ()2-s2.0-27444444125 (Scopus ID)
Note

QC 20101005. Uppdaterad från Accepted till Published (20101005).

Available from: 2006-09-14 Created: 2006-09-14 Last updated: 2012-10-02Bibliographically approved
3. Surface modification of wood fibers using the polyelectrocyte multilayer technique: Effects on fiber joint and paper strength properties
Open this publication in new window or tab >>Surface modification of wood fibers using the polyelectrocyte multilayer technique: Effects on fiber joint and paper strength properties
2006 (English)In: Industrial & Engineering Chemistry Research, ISSN 0888-5885, E-ISSN 1520-5045, Vol. 45, 5279-5286 p.Article in journal (Refereed) Published
Abstract [en]

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

Keyword
weak polyelectrolytes, dry strength, starch
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-6118 (URN)10.1021/ie060226w (DOI)000238973200014 ()2-s2.0-33746907494 (Scopus ID)
Note

QC 20100923

Available from: 2006-09-14 Created: 2006-09-14 Last updated: 2012-10-02Bibliographically approved
4. Application of polymeric multilayers of starch onto wood fibres to enhance strength properties of paper
Open this publication in new window or tab >>Application of polymeric multilayers of starch onto wood fibres to enhance strength properties of paper
2005 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 20, no 3, 270-276 p.Article in journal (Refereed) Published
Abstract [en]

Polyelectrolyte multilayers of cationic and anionic starch have been used to enhance the strength properties of paper. All starches used in this investigation had a degree of substitution around 0.065. Optical reflectometry showed that a combination of cationic and anionic starch could form polyelectrolyte multilayers onto silicon oxide surfaces. The same combination of starches was then applied to unbeaten, bleached softwood kraft fibres to form three layers, i.e. a cationic/anionic/cationic starch combination. The results showed a significant increase in the paper strength properties in terms of tensile index, strain at break, and Scott Bond. The adsorbed amount of starch in the sheets, determined using an enzymatic method, was found to increase with each successive starch treatment. The increased paper strength was not only due to the increase in adsorbed amount of starch; rather, the chemical composition of the starch was also important. Cationic starch with high amylose content had a more positive effect on the paper strength properties. Furthermore, it was observed that anionic starch, despite being adsorbed in large amounts, did not contribute to the increase in tensile strength or strain at break to the same extent as did cationic starch. However, the out-of-plane properties, measured as Scott Bond properties, increased with the adsorbed amount, regardless of the chemical composition of the starch used in the outermost layer.

Keyword
polyelectrolyte, multilayer, adsorption, optical reflectometry, potato starch, anionic starch, cationic starch, paper strength
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-6119 (URN)10.3183/NPPRJ-2005-20-03-p270-276 (DOI)000235257900002 ()2-s2.0-27344445449 (Scopus ID)
Note

QC 20100830

Available from: 2006-09-14 Created: 2006-09-14 Last updated: 2012-10-02Bibliographically approved
5. The role of polymer compatibility in adhesion between surfaces saturated with modified dextrans
Open this publication in new window or tab >>The role of polymer compatibility in adhesion between surfaces saturated with modified dextrans
2007 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 310, no 1, 312-320 p.Article in journal (Refereed) Published
Abstract [en]

Wet and dry adhesion between dextran-coated surfaces were measured aiming to understand the influence of polymer compatibility. The wet adhesion measurements were performed using the atomic force microscope (AFM) colloidal probe technique whereas the dry adhesion measurements were performed using the micro adhesion measurement apparatus (MAMA). Two types of dextrans were used, one cationically modified dextran (DEX) and one that was both cationically and hydrophobically modified (HDEX), leading to three different combinations of polymer-coated surfaces; (1) DEX:DEX, (2) HDEX:DEX, and (3) HDEX:HDEX. DEX increased dry adhesion more than HDEX did, which likely is due to differences in the ability to form specific interactions, especially hydrogen bonding. HDEX gave strong wet adhesion, probably due to its poorer solvency, while DEX contributed to reducing the wet adhesion due to its hydrophilicity. All combinations showed a steric repulsion on approach in aqueous media. Furthermore, when HDEX was adsorbed on either or both surfaces a long range attractive force between the surfaces was detected outside this steric regime.

Keyword
adhesion, interaction forces, polymer, adsorption, incompatible, asymmetric, cationic dextran, hydrophobic, hydrophilic, AFM, colloidal probe technique, JKR
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-6120 (URN)10.1016/j.jcis.2007.01.089 (DOI)000245967500038 ()2-s2.0-34147094843 (Scopus ID)
Note

QC 20110125. Uppdaterad från manuskript till artikel(20110125)

Available from: 2006-09-14 Created: 2006-09-14 Last updated: 2012-10-02Bibliographically approved
6. Surface Forces Measurements of Spin-Coated Cellulose Thin Films with Different Crystallinity
Open this publication in new window or tab >>Surface Forces Measurements of Spin-Coated Cellulose Thin Films with Different Crystallinity
Show others...
2006 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 22, no 7, 3154-3160 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
COLLOIDAL PROBE MICROSCOPY, MODEL FILMS, IONIC-STRENGTH, I SURFACES;, POLYELECTROLYTE, ELECTROLYTE, SUSPENSIONS, FIBERS, SILICA, MICA
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-6121 (URN)10.1021/la052886w (DOI)000236843300040 ()2-s2.0-33645546475 (Scopus ID)
Note

QC 20100930

Available from: 2006-09-14 Created: 2006-09-14 Last updated: 2012-10-02Bibliographically approved
7. Effects of crystallinity on adhesion
Open this publication in new window or tab >>Effects of crystallinity on adhesion
(English)Manuscript (Other academic)
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-6122 (URN)
Note
QC 20110125Available from: 2006-09-14 Created: 2006-09-14 Last updated: 2011-01-25Bibliographically approved

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