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Polyelectrolyte Complexes: Their Characterization and use for Modification of Wood Fibre Surfaces
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
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: urn:nbn:se:kth:diva-4225OAI: oai:DiVA.org:kth-4225DiVA: diva2:11327
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
List of papers
1. New insights into the structure of polyelectrolyte complexes
Open this publication in new window or tab >>New insights into the structure of polyelectrolyte complexes
2007 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 312, no 2, 237-246 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
polyelectrolyte complex, poly(acrylic acid), poly(niethacrylic acid), poly(allylamine hydro chloride), structure, water content, Cryo-TEM, AFM, light scattering, poly-electrolyte complexes, light-scattering, supermolecular structures, cationic polymers, adsorption, dispersions, improvement, microscopy, particles, strength
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-16769 (URN)10.1016/j.jcis.2007.03.075 (DOI)000247838300008 ()2-s2.0-34250687914 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2010-08-25Bibliographically approved
2. Polyelectrolyte complexes for surface modification of wood fibres - I. Preparation and characterisation of complexes for dry and wet strength improvement of paper
Open this publication in new window or tab >>Polyelectrolyte complexes for surface modification of wood fibres - I. Preparation and characterisation of complexes for dry and wet strength improvement of paper
2003 (English)In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, Vol. 213, no 1, 15-25 p.Article in journal (Refereed) Published
Abstract [en]

Polyelectrolyte complexes (PEC) were formed between a cationic polyamideamine epichlorohydrine condensate (PAE) and an anionic carboxymethylcellulose (CMC) at different ratios between the polymers, orders of mixing, salt concentrations and polymer concentrations. Initially the polymers were characterised by polyelectrolyte titration (charge), static light scattering (molecular weight, radius of gyration) and measurements with a scanning interferometric refractometer (refractive index). The complexes were characterised by ocular inspection and static light scattering in combination with a special evaluation algorithm allowing an estimation of the geometric form of the complexes. The results show that the initial complexes have a spherical form and that the size is fairly constant over a large range of charge ratios between the polymers, provided the complexes are formed in deionised water. When the charge mixing ratio exceeded neutrality a secondary agglomeration of the initially formed complexes occurred. The presence of salt during PEC formation caused a dependence of the level of aggregation on the mixing ratio, whereby small amounts of NaCl drastically lowered the particle mass at lower mixing ratios. Subsequent addition of salt to PECs formed in water led to a strong swelling of the complex particles and at a critical salt concentration to dissolution.

Keyword
agglomeration, complex compounds, density, electrostatic charge, mixing, molecular structure, molecular weight, polyelectrolytes, radius of gyration, ratios, sphere, stability, poly-electrolyte complexes, streaming current detector, adsorption, systems
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-22487 (URN)000182771400003 ()
Note
QC 20100525Available from: 2010-08-10 Created: 2010-08-10 Last updated: 2010-08-25Bibliographically approved
3. Smooth model surfaces from lignin derivatives. II. Adsorption of polyelectrolytes and PECs monitored by QCM-D
Open this publication in new window or tab >>Smooth model surfaces from lignin derivatives. II. Adsorption of polyelectrolytes and PECs monitored by QCM-D
Show others...
2007 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, no 7, 3737-3743 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
atomic-force microscopy, langmuir-blodgett-films, strength properties, cellulose surfaces, joint strength, wood fibers, lb films, complexes, morphology, spectroscopy
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-16461 (URN)10.1021/la063439z (DOI)000245012900034 ()2-s2.0-34147193023 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2010-08-25Bibliographically approved
4. Polyelectrolyte complexes for surface modification of wood fibres II. Influence of complexes on wet and dry strength of paper
Open this publication in new window or tab >>Polyelectrolyte complexes for surface modification of wood fibres II. Influence of complexes on wet and dry strength of paper
2003 (English)In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, Vol. 218, no 1-3, 137-149 p.Article in journal (Refereed) Published
Abstract [en]

The current paper presents a way of enhancing paper strength by the use of polyelectrolyte complexes (PEC) of cationic poly(amideamine) epichlorohydrin condensate (PAE) and anionic carboxymethylcellulose (CMC). In this study the complexes were pre-formed in different mixing ratios, but with an overall anionic charge. The complexes were characterized by means of size, charge, and adsorption properties both to fibres and to model silica surfaces. Finally the PECs were applied as strength additive in paper sheet preparation. The main findings are that by changing polymer weight-ratios when preparing the complexes the charge and the amount adsorbed could be altered. Addition of the complexes to the fibres before sheet preparation led to a significant increase in strength of the paper, compared to sheets prepared with only the PAE. The strength improvement depended upon the mixing ratio and a maximum in dry strength was found for complexes where the anionic charge of the CMC had been neutralized to 60%.

Keyword
paper strength, polyelectrolyte complexes, poly(amide, amine) epichlorohydrin, carboxymethylcellulose, strength additive, self-diffusion, adsorption, reflectometry, salt
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-22585 (URN)10.1016/s0927-7757(02)00588-5 (DOI)000183508500012 ()
Note
QC 20100525Available from: 2010-08-10 Created: 2010-08-10 Last updated: 2010-08-25Bibliographically approved
5. Influence of polyelectrolyte complexes on the strength properties of papers from unbleached kraft pulps with different yields
Open this publication in new window or tab >>Influence of polyelectrolyte complexes on the strength properties of papers from unbleached kraft pulps with different yields
2005 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, 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.

Keyword
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:nbn:se:kth:diva-14688 (URN)000228457000006 ()2-s2.0-17044434302 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2010-08-25Bibliographically approved
6. The use of polyelectrolyte complexes (PEC) as strength additives for different pulps used for production of fine paper
Open this publication in new window or tab >>The use of polyelectrolyte complexes (PEC) as strength additives for different pulps used for production of fine paper
2007 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 22, no 2, 210-216 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
adsorption, beating, polyelectrolytes, polyelectrolyte complexes, tensile properties, surface modification, wood fibers, topochemical modification, carboxymethyl cellulose, dry-strength, part i, wet, performance, attachment
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-16795 (URN)10.3183/NPPRJ-2007-22-02-p210-216 (DOI)000248057800010 ()2-s2.0-34547316429 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2010-08-25Bibliographically approved

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