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Formation and properties of polyelectrolyte multilayers on wood fibres:  influence on paper strength and fibre wettability
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
2006 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

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

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

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

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

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

Abstract [sv]

Denna licentiatavhandling behandlar adsorption av polyelektrolytmultiskikt (multiskikt) på cellulosafibrer som ett nytt sätt att påverka en fibers ytegenskaper. Grundläggande förutsättningar för bildandet av multiskikt på fibrer diskuteras i termer av pappersstyrka och fibervätning.

Multiskikt har bildats med hjälp av tre olika polymerkombinationer; 1.) två starka polyelektrolyter, polydiallyldimetylammoniumklorid (PDADMAC) och polystyrensulfanat (PSS), 2.) polyetylenoxid (PEO) och polyakrylsyra (PAA), adsorberade vid lågt pH och sammanhållna av icke elektrostatiska vätebindningar, och 3.) två svaga polyelektrolyter, polyallylaminhydroklorid (PAH) och PAA. Uppbyggnaden av multiskikt bestående av PDADMAC/PSS och PEO/PAA på kiseloxid studerades med Stagnationspunktsreflektometri (SPAR) för att undersöka att uppbyggnad av PEM skett, samt att studera hur uppbyggnaden påverkas av koncentrationen NaCl i polymerlösningen. Försöken visade att den adsorberade mängden PDADMAC/PSS ökade med saltkoncentrationen upp till 0,05-0,1 M NaCl. Uppbyggnaden av multiskikt bestående av PAH/PAA är sedan tidigare studerad undersöks därför inte specifikt i detta arbete.

Laboratorieark tillverkades av fibrer som behandlats med multiskikt bestående av PDADMAC/PSS, respektive PAH/PAA. Fysikalisk pappersprovning av arken visade för båda systemen en ökning med cirka 100 % i dragindex för ark som tillverkats av fibrer som behandlats med cirka tio lager, jämfört med ark som tillverkats av icke-behandlade fibrer. Ark tillverkade från PDADMAC/PSS-behandlade fibrer visade att när 5-7 lager adsorberats, ett högre dragindex då PDADMAC adsorberats i det yttersta lagret, jämfört med då PSS adsorberats i det yttersta lagret. Ark tillverkade från fibrer behandlade med PEO/PAA visade ingen skillnad i dragindex beroende av vilken polymer som adsorberats i det yttersta lagret.

Den adsorberade mängden PDADMAC/PSS på fibrerna bestämdes med hjälp av kväve- respektive svavelanalys. Den adsorberade mängden polymer ökad linjärt som en funktion av antalet adsorberade lager, men med en högre adsorberad mängd i det första lagret. Dessa resultat har jämförts med den adsorberade mängden för multiskikt uppbyggda med SPAR på kiseloxid. Jämförelsen visade att det finns skillnader i uppbyggnaden mellan skikt byggda på kiseloxid och fibrer, men att kiseloxid med god tillförlitlighet kan användas som modellyta för att förutsäga generella trender för adsorptionen av samma polymersystem på cellulosafibrer.

Multiskikt har också bildats på enskilda fibrer med hjälp av en dynamisk kontaktvinkelmätare (DCA). Genom att behandla en del av en fiber, och jämföra den behandlade delen med den obehandlade delen på samma, kan ett multiskikts inverkan på fiberns ytstruktur och vätningsegenskaper studeras. De olika polymersystemen visade en avsevärd skillnad i förmågan att påverka en fibers vätningsegenskaper. För fibrer behandlade med PAH/PAA är också pH av stor betydelse för graden inverkan på fiberns vätningsegenskaper. Fibrer behandlade med PDADMAC/PSS och PAH/PAA, visade en sämre vätningsförmåga då den katjoniska polymeren adsorberats i det yttersta lagret, och vice versa. För enskilda fibrer behandlade med PEO/PAA, kunde inte konstateras någon skillnad beroende av vilken polymer som adsorberats i det yttersta lagret.

Vid en jämförelse mellan vätningsförmåga och pappersstyrka kan konstateras att de ark som visade den högsta styrkan tillverkats av fibrer där den lägsta vätningsförmågan har kunnat konstateras. Denna skillnad kan diskuteras med utgångspunkten i att en lägre vätningsförmåga resulterar i en högre våt adhesion och därmed en starkare interaktion mellan de polymerbehandlade ytorna i vått tillstånd. Det föreslås i avhandlingen att den ökade kraft som detta resulterar i vid bildandet av en fiber-fiberfog ger upphov till en högre kontaktarea och därmed, förmodligen, också en högre torr adhesion. Kraftmätningar i vått tillstånd för behandlade kiselmodellytor med hjälp av atomkraftsmikroskopi (AFM) har för PAH/PAA visat att den våta adhesionen är högre då PAH är adsorberats i det yttersta lagret, jämfört med då PAA adsorberats i det yttersta lagret. Detta stödjer hypotesen att en lägre vätning gynnar uppkomsten av en stark fiber-fiberfog.

Place, publisher, year, edition, pages
Stockholm: KTH , 2006. , 30 p.
Series
Trita-FPT-Report, ISSN 1652-2443 ; 2006:12
Keyword [en]
polyelectrolyte, multilayer, adsorption, reflectance, contact angle, dynamics, paper, mechanical properties, individual, wood fibre
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-4062OAI: oai:DiVA.org:kth-4062DiVA: diva2:10599
Presentation
2006-06-14, STFI-salen, STFI-Packforsk, Drottning Kristinas väg 61, Stockholm, 14:00
Supervisors
Note
QC 20101118Available from: 2006-06-25 Created: 2006-06-25 Last updated: 2010-11-18Bibliographically approved
List of papers
1. Formation of polyelectrolyte multilayers on fibres: Influence on wettability and fibre/fibre interaction
Open this publication in new window or tab >>Formation of polyelectrolyte multilayers on fibres: Influence on wettability and fibre/fibre interaction
2006 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 296, no 2, 396-408 p.Article in journal (Refereed) Published
Abstract [en]

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

Keyword
polyelectrolyte; multilayer; adsorption; optical measurements; reflectance; contact angle; dynamics; environmental scanning electron microscopy; paper; mechanical properties
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-6022 (URN)10.1016/j.jcis.2005.09.017 (DOI)000236424600003 ()2-s2.0-33644987360 (Scopus ID)
Note

QC 20100823

Available from: 2006-06-25 Created: 2006-06-25 Last updated: 2015-05-26Bibliographically approved
2. Wettability changes in the formation of polymeric multilayers on cellulose fibres and their influence on wet adhesion
Open this publication in new window or tab >>Wettability changes in the formation of polymeric multilayers on cellulose fibres and their influence on wet adhesion
2007 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 314, no 1, 1-9 p.Article in journal (Refereed) Published
Abstract [en]

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

Keyword
polyelectrolyte; multilayer; adsorption; reflectance; contact angle; dynamics; paper; mechanical properties; individual; wood fibre
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-8744 (URN)10.1016/j.jcis.2007.04.046 (DOI)000248795100001 ()2-s2.0-34547514213 (Scopus ID)
Note
QC 20100823Available from: 2008-06-13 Created: 2008-06-13 Last updated: 2010-11-18Bibliographically approved

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