| 1. |
- Ankerfors, Caroline, et al.
(författare)
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A comparative study of polyelectrolyte multilayers and other chemical dosage strategies : Effect on properties of paper sheets produced in laboratory scale using tap and mill process waters
- 2018
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this study, the addition of up to four layers of PEM was studied and compared with the use of single-additions or dual-additions of the same chemicals with respect to their effect on strength and bulk properties of paper sheets produced in the laboratory. First, this was made under clean conditions, i.e. in tap water, to set a baseline for the performance. The systems studied were cationic/anionic polyacrylamide (CPAM/APAM), polyvinylamine/carboxymethyl cellulose (PVAm/CMC) and cationic starch/anionic polyacrylamide (CS/APAM).One of the main findings of the study was that with single-additions with increasing dosage levels of PVAm, CPAM or CS, the tensile strength index of the produced sheets increased at first, but the effect seemed to level off at higher dosages. By comparing the effect from single-addition of each cationic component to the effect of a polyelectrolyte multilayer (1-4 layers) of the same component together with an anionic component, it was found that significantly higher tensile strength could be reached with the PEM strategy for the combinations PVAm/CMC and CS/APAM. For CPAM/APAM, however, very little advantage of using a multilayering approach was seen.All measured variations in sheet density were small, although with some indications that the density was lower for sheets with PEM, medium for sheets made with a single-dosage strategy and highest for sheets made with the dual-addition strategies.The later part of this activity also addressed the influence from dissolved and colloidal substances (DCS) to investigate the possibilities of implementing the polyelectrolyte multilayering technique in practice by repeating some of the trial points of the CS/APAM system in mill process water. Firstly, this part of the study showed that PEMs can be successfully built in mill process waters. Further, it was found that although the adsorbed amounts might differ compared to in the cleaner system, the trends for the dosage strategies and their strengthening effects remained.
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| 2. |
- Ankerfors, Caroline, et al.
(författare)
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A comparison of polyelectrolyte complexes and multilayers : Their adsorption behaviour and use for enhancing tensile strength of paper
- 2009
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Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 24:1, s. 77-86
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Tidskriftsartikel (refereegranskat)abstract
- This paper compares the adsorption behaviour and paper-strength-enhancing properties of polyelectrolyte complexes (PECs) and polyelectrolyte multilayers (PEMs) of polyallylamine hydrochloride and polyacrylic acid. Model adsorption experiments using SPAR (stagnation point adsorption reflectometry) and QCM-D (quartz crystal microbalance with dissipation) showed that the amount of complexes adsorbed was lower than the amount adsorbed when forming a multilayer using the same polymer system. From these experiments, in combination with AFM and ESEM imaging, it was concluded that the PEC adsorption stopped before full surface coverage was reached. Tensile testing of handsheets treated with PECs and PEM showed a significant increase in both tensile index and strain-at-break using both systems. The largest strength improvement was achieved with the fibres treated with the largest number of PEMs, but the largest effect per adsorbed amount of polymer was achieved by PEC treatment.
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| 3. |
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| 4. |
- Ankerfors, Caroline, et al.
(författare)
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AFM adhesion imaging for the comparison of polyelectrolyte complexes and polyelectrolyte multilayers
- 2012
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 8:32, s. 8298-8301
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Tidskriftsartikel (refereegranskat)abstract
- The adhesion and topography of dry surfaces treated with polyelectrolyte complexes (PECs) and multilayers (PEMs) of PAH/PAA or CPAM/silica nanoparticles were studied using AFM adhesion mapping. PEMs gave higher adhesion than did PECs for the PAH/PAA system, but adhesion did not differ significantly between PEMs and PECs for the CPAM/silica system. The latter system displayed multiple release patterns, interpreted as disentanglements and tentatively ascribed to nanoparticle presence. AFM adhesion mapping is valuable for analysing PEC and PEM. The measurements should, however, be combined with separate force measurements for a more complete picture of the adhesion.
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| 5. |
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| 6. |
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| 7. |
- Ankerfors, Caroline, et al.
(författare)
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Final Report for the Source-Efficient Paper and Board Making Research Programme Area
- 2018
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This is the final report for the Innventia/RISE Bioeconomy research programme area “Source-Efficient Paper and Board Making”, which was executed 2015-2017.The overall aim of the Source Efficient Paper and Board Making was to improve the resource efficiency in paper and board production. This was achieved by combining paper chemistry, paper physics and process technology. A particular goal was to reduce raw material consumption through the use of stronger materials or creation of bulk, which are needed to maintain bending stiffness and mechanical properties if the grammage is reduced. The work in the project has been carried out in laboratory scale and in pilot scale using the FEX pilot paper machine and the dynamic flow loop.
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| 8. |
- Ankerfors, Caroline, 1979-
(författare)
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Polyelectrolyte complexes : Preparation, characterization, and use for control of wet and dry adhesion between surfaces
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis examines polyelectrolyte complex (PEC) preparation, adsorption behaviour, and potential use for control of wet and dry adhesion between surfaces. PEC formation was studied using a jet-mixing method not previously used for mixing polyelectrolytes. The PECs were formed using various mixing times, and the results were compared with those for PECs formed using the conventional polyelectrolyte titration method. The results indicated that using the jet mixer allowed the size of the formed PECs to be controlled, which was not the case with the polyelectrolyte titration method, and a two-step mechanism for PEC formation was suggested. Adsorption experiments comparing two types of PECs, both produced from PAA and PAH, but with different molecular weights, demonstrated that surface-induced aggregation occurred in the high-molecular-weight PECs, whereas the adsorption stopped at a low level in the low-molecular-weight PECs. It was suggested that the latter PECs consisted of two fractions of complexes and that the fraction with lower polymer density exerted a site-blocking effect, hindering further adsorption. It was also demonstrated that particle-PECs (PPECs), in which one polyion was replaced with a silica nanoparticle, could be prepared. The purpose of preparing PPECs was to create a PEC structure that could create a joint with a special failure pattern referred to as disentanglement behaviour. Using the colloidal probe AFM technique, the expected disentanglement could be detected in PPECs, though the joint strength was low. Adhesion experiments demonstrated significantly higher pull-off values with polymer–polymer complexes than with PPECs. However, there was large spread in the data, possibly due to the surface inhomogeneity. Experiments using low-molecular-weight PECs as a paper strength agent demonstrated that PECs can indeed increase paper strength. Comparing the PEC results with those for polyelectrolyte multilayers (PEMs) prepared from the same polyelectrolytes indicated that, since the PEM strategy enables higher adsorption levels than does the PEC strategy, greater absolute strength improvements could be achieved using PEMs. However, PEC treatment resulted in the greatest effect per adsorbed amount of polymer.
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| 9. |
- Ankerfors, Caroline
(författare)
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Polyelectrolyte complexes : their preparation, adsorption behaviour and effect on paper properties
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this work, the formation of polyelectrolyte complexes (PECs) has been studied using a jet mixing method not previously used for mixing polyelectrolytes. The PECs were formed from two weak polyelectrolytes, i.e., polyacrylic acid (PAA) and polyallylamine hydrochloride (PAH), with different mixing times, and the results were compared with those for PECs formed using the conventional polyelectrolyte titration method. The adsorption behaviour of the formed PECs on silicon oxide substrates and pulp fibres was analysed, and the results were compared with those for polyelectrolyte multilayers (PEMs) prepared from the same two polyelectrolytes. The results indicated that by using the jet mixer, the size of the formed PECs could be controlled, which was not the case with the polyelectrolyte titration method. The PECs produced by jet mixing were also found to be smaller than those produced by polyelectrolyte titration. From these results, a two-step mechanism for the formation of PECs was suggested: initial precomplex formation, which is a fast and diffusion-controlled process, followed by a reconformation process, during which the vigorous mixing in the jet mixer can partially limit secondary aggregation. When the complexes were adsorbed to silicon oxide or pulp fibre surfaces, adsorption studies indicated that it was impossible to reach the same adsorption levels for PECs as for PEMs. This was explained in terms of free energy, entropical, reasons rather than to any geometric limitation of the surface. Despite the smaller amount of polyelectrolyte adsorbed from the PEC treatment than from the PEM treatment of pulp fibres, the PEC treatment had the greatest effect on paper strength per adsorbed amount of polymer. This was thought to be because the three-dimensional structure of the PECs, versus the smoother structure of PEMs, allows for the formation of multiple contact points between the macroscopically rough fibres and increased molecular contact area. In the adsorption experiments, it was also found that net cationic complexes can adsorb to both anionic and cationic substrates. This phenomenon was explained by the occurrence of anionic patches on the surface of the net cationic PECs and the ability of the PECs, formed from weak polyelectrolytes, to partially change charge upon exposure to a surface of the same charge as the complex itself, due to a change of the degree of dissociation of the polyelectrolytes constituting the complex.
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| 10. |
- Ankerfors, Caroline, et al.
(författare)
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Polyelectrolyte Complexes for Tailoring of Wood Fibre Surfaces
- 2014
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Ingår i: Polyelectrolyte Complexes In The Dispersed And Solid State II. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 0065-3195 .- 1436-5030. - 9783642407468 - 9783642407451 ; , s. 1-24
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Bokkapitel (refereegranskat)abstract
- The use of polyelectrolyte complexes (PECs) provides new opportunities for surface engineering of solid particles in aqueous environments to functionalize the solids either for use in interactive products or to tailor their adhesive interactions in the dry and/or wet state. This chapter describes the use of PECs in paper-making applications where the PECs are used for tailoring the surfaces of wood-based fibres. Initially a detailed description of the adsorption process is given, in more general terms, and in this respect both in situ formed and pre-formed complexes are considered. When using in situ formed complexes, which were intentionally formed by the addition of oppositely charged polymers, it was established that the order of addition of the two polyelectrolytes was important, and by adding the polycation first a more extensive fibre flocculation was found. PECs can also form in situ by the interaction between polyelectrolytes added and polyelectrolytes already present in the fibre suspension originating from the wood material, e. g. lignosulphonates or hemicelluloses. In this respect the complexation can be detrimental for process efficiency and/or product quality depending on the charge balance between the components, and when using the PECs for fibre engineering it is not recommended to rely on in situ PEC formation. Instead the PECs should be pre-formed before addition to the fibres. The use of pre-formed PECs in the paper-making process is described as three sub-processes: PEC formation, adsorption onto surfaces, and the effect on the adhesion between surfaces. The addition of PECs, and adsorption to the fibres, prior to formation of the paper network structure has shown to result in a significant increase in joint strength between the fibres and to an increased strength of the paper made from the fibres. The increased joint strength between the fibres is due to both an increased molecular contact area between the fibres and an increased molecular adhesion. The increased paper strength is also a result of an increased number of fibre/fibre contacts/unit volume of the paper network.
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| 11. |
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| 12. |
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| 13. |
- Ankerfors, Caroline, et al.
(författare)
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Use of polyelectrolyte complexes and multilayers from polymers and nanoparticles to create sacrificial bonds between surfaces
- 2013
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 391, s. 28-35
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Tidskriftsartikel (refereegranskat)abstract
- In this study, particle polyelectrolyte complexes (PPECs) were formed by mixing cationic polyacrylamide (CPAM) and silica nanoparticles using the jet mixing technique. Within certain limits, the size of the formed PPECs could be controlled. The aim was to prepare PPECs with embedded sacrificial bonds, similar to those found in bones. Examination of PPEC adsorption to silica model surfaces indicated that,smaller PPECs adsorbed to a higher level than larger ones, due to the higher diffusion speed of smaller complexes. Adsorption studies of the same components as in the PPECs, but arranged in multilayers, that is, particle polyelectrolyte multilayers (PPEMs), indicated a stable, gradual build-up of material on the surface with smaller nanoparticles, whereas PPEMs comprising elongated nanoparticles appeared to be more loosely adsorbed onto the surface when the nanoparticles were in the outer layer, due to repulsive forces within the adsorbed layer. The AFM colloidal probe technique was used to study the interaction between surfaces treated with PPECs, multilayers, or polyelectrolyte complexes (PECs). The results showed that the expected long-range disentanglement could be achieved with PPECs but that the pull-off forces were generally low. Treatment with PPEMs comprising the same polymer and nanoparticle components produced higher pull-off values, together with disentanglement behaviour, possibly due to better contact between the surfaces. Adhesion experiments with polymer PECs showed significantly higher pull-off values than with the PPECs, probably due to polymer interdiffusion across the surface boundary.
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| 14. |
- Ankerfors, Caroline, et al.
(författare)
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Using jet mixing to prepare polyelectrolyte complexes : Complex properties and their interaction with silicon oxide surfaces
- 2010
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 351:1, s. 88-95
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Tidskriftsartikel (refereegranskat)abstract
- The influence of mixing procedure on the properties of polyelectrolyte complexes (PECs) was investigated using two complexation techniques, polyelectrolyte titration and jet mixing, the latter being a new method for PEC preparation. For the low-molecular-weight polyelectrolytes polyacrylic acid (PAA) and polyallyl amine hydrochloride (PAH), shorter mixing times produced smaller PECs, whereas for higher molecular weights of the same polyelectrolytes, PEC size first decreased with decreasing mixing time to a certain level, after which it started increasing again. This pattern was likely due to the diffusion-controlled formation of "pre-complexes", which, in the case of low-molecular-weight polymers, occurs sufficiently quickly to form stable complexes; when polyelectrolytes are larger, however, non-equilibrium pre-complexes, more prone to aggregation, are formed. Comparing the techniques revealed that jet mixing produced smaller complexes, allowing PEC size to be controlled by mixing time, which was not the case with polyelectrolyte titration. Higher polyelectrolyte concentration during jet mixing led to the formation of larger PECs. It was also demonstrated that PEC size could be changed after preparation: increasing the pH of the PEC dispersion led to an irreversible increase in PEC size, whereas lowering the pH did not influence PEC size. The adsorption behavior of PECs formed from weak polyelectrolytes on model substrates was studied using QCM-D, SPAR, and AFM imaging; the results indicated that increasing the pH increased the amount of PECs adsorbed to model surfaces. However, the amount of PECs adsorbed to the model surfaces was low compared with other systems in all studied cases.
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| 15. |
- Krochak, Paul, et al.
(författare)
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Possible benefits of adding retention aids as well as cationic starch for dry strength very close to the headbox
- 2017
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Ingår i: Paper Conference and Trade Show. - : TAPPI Press. ; , s. 695-704
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Previous research made at RISE Bioeconomy (former Innventia) has shown significant improvements to both retention and formation when retention AIDS, cationic polyacrylamide (C-PAM) and microparticulate silica, were added very close to the headbox given that the mixing was adequate. The pilot trial that showed these results used a somewhat idealised system since the furnish used consisted solely of fibre, filler and retention aid. In addition to these components, it is very common to add some cationic starch to the thick stock to increase the paper strength. When cationic starch (0.5%) had been added to the thick stock there was no longer any obvious positive effect on the retention-formation relationship with the late dosage of the retention system. This spurred a further investigation and trials in which also the cationic starch was added just prior to the headbox, such that the contact times of all three components (C-PAM, microparticulate silica and cationic starch) were less than 3 seconds prior to forming. Also in these cases, the general positive effect on the formation-retention relationship was not seen, but the C-PAM dosage needed to obtain a certain retention level was much less as compared to when the normal dosage positions were used. This clearly demonstrates possibilities to drastically decrease the C-PAM consumption. Only marginal negative effect on the mechanical properties of the produced paper was seen when the starch was added just prior to the headbox as compared to in the thick stock. It is common wisdom that starch should have a long contact time to give optimal strength gain. The presented results show that this needs not to be the case, and the key is probably adequate mixing.
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| 16. |
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| 17. |
- Larsson, Per Tomas, et al.
(författare)
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Bulking method for chemical pulps and its effect on cellulose structure - A CP/MAS 13C-NMR Study
- 2021
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Ingår i: TAPPICon LIVE. - : TAPPI Press. - 9781713848370 ; , s. 460-464
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Konferensbidrag (refereegranskat)abstract
- Cellulose-rich never-dried acetate grade Eucalyptus dissolving pulp was used to study the effects on the supramolecular structure of cellulose due to the addition of AlCl3 during drying from acidic conditions (pH 3.5). CP/MAS 13C-NMR was the analytical technique used for taking measures of the cellulose supramolecular structure. In this study AlCl3 was used as source of Al3+, but Al2(SO4)3 has been shown to give the same effect and it is believed that any salt of Al3+ will give the same effect. The presence of AlCl3 increased the average lateral fibril aggregate dimensions some 25% above that reached by the pulp dried without addition of AlCl3. The observed changes in cellulose supramolecular structure due to the addition of AlCl3 are large considering the low AlCl3 concentration that was used. No change in degree of crystallinity was observed as the result of drying, either with or without AlCl3 addition. Although the mechanism of action for AlCl3, causing the observed effects on the cellulose supramolecular structure, is currently not fully understood, the interpretation made was that the presence of AlCl3 increased the agglomeration of the cellulose that always take place during the first drying of cellulosic fibres. This can be seen as an increased degree of physical cross-linking in the cellulose network.
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| 18. |
- Ondaral, Sedat, et al.
(författare)
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Surface-Induced Rearrangement of Polyelectrolyte Complexes : Influence of Complex Composition on Adsorbed Layer Properties
- 2010
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 26:18, s. 14606-14614
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption characteristics of two different types of polyelectrolyte complexes (PECs). prepared by mixing poly(allylamine hydrochloride) and poly(acrylic acid) in a confined impinging jet (CIJ) mixer, have been investigated with the aid of stagnation point adsorption reflectometry (SPAR), a quartz crystal microbalance with dissipation (QCM-D), and atomic force microscopy (A FM) using SiO2 surfaces The two sets of PEC were prepared by combining high molecular mass PAH/FAA (PEC-A) and low molt:cubit mass PAH/PAA (PEC-B) The PEC-A showed a higher adsorption to the SiO2 surfaces than the PEC-B The adsorption of the PEC-A also showed a larger change in the dissipation (AD), according to the QCM-D measurements, suggesting that the adsorbed layer of these complexes had a relatively lower viscosity and a lower shear modulus Complementary investigations of the adsorbed layer using A FM imaging showed that the adsorbed layer of PEC-A was significantly different from that of PEC-B and that the changes in properties with adsorption time were very different for the two types of PECs The PEC-A complexes showed a coalescence into larger block of complexes on the SiO2 surface, but this was not detected with the PEC-B The size determinations of the complexes in solution showed that they were very stable over time, and it was therefore concluded that the coalescence of the complexes was induced I the interaction between the complexes and the surface The results also indicated that polyelectrolytes can migrate between the different complexes adsorbed to the surface The results also give indications that the preparation of PEC-B leads to the formation of two different types of polyelectrolyte complexes differing in the amount of polymer in the complexes: i.e., two populations of complexes were formed with similar sizes but with totally different adsorption structures at the solid-liquid interface.
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| 19. |
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