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Influence of polyelectrolyte complexes on the strength properties of papers from unbleached kraft pulps with different yields
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.ORCID iD: 0000-0001-8622-0386
2005 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 20, no 1, 36-42 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2005. Vol. 20, no 1, 36-42 p.
Keyword [en]
adsorption, polyelectrolyte complexes, compression strength, polyelectrolytes, strength properties, unbleached pulp, pulp yield, dry strength, wet, fibers, relaxation, mechanism, systems
National Category
Paper, Pulp and Fiber Technology
Identifiers
URN: urn:nbn:se:kth:diva-14688ISI: 000228457000006Scopus ID: 2-s2.0-17044434302OAI: oai:DiVA.org:kth-14688DiVA: diva2:332729
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Polyelectrolyte Complexes: Their Characterization and use for Modification of Wood Fibre Surfaces
Open this publication in new window or tab >>Polyelectrolyte Complexes: Their Characterization and use for Modification of Wood Fibre Surfaces
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

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.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. 61 p.
Series
Trita-FPT-Report, ISSN 1652-2443 ; 2006:42
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-4225 (URN)
Public defence
2006-12-15, SCA salen, Mittuniversitet, Holmgatan 10, Sundsvall, 13:00
Opponent
Supervisors
Note
QC 20100825Available from: 2006-12-12 Created: 2006-12-12 Last updated: 2010-08-25Bibliographically approved

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