| 1. |
- Duker, Elisabeth, et al.
(författare)
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The use of CMC as a dry strength agent - the interplay between CMC attachment and drying.
- 2008
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Ingår i: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 23:1, s. 65-71
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Tidskriftsartikel (refereegranskat)abstract
- This paper deals with the ability to use high molecular weight CMC as a dry strength agent in paper and how the drying of the pulp, either before or after the CMC attachment, affects the mechanical properties of the paper. The effect of the counter-ion form used during drying and reslushing was also investigated. In the case of the calcium and hydrogen counter-ion forms, drying after CMC attachment had no impact on the attached amount. The sodium form did, however, result in some detachment of CMC. When the pulp was dried prior to CMC treatment, the counter-ion form had no effect on the attached amount. It was also shown that drying of a CMC-treated pulp reduced the positive effect of CMC on the mechanical properties. Nevertheless, the mechanical properties were still better than those of paper made from the never-dried reference pulp. The relative effect of CMC on the mechanical properties was independent of the drying strategy used and the counter-ion form did not affect the mechanical properties. However, surface carboxymethylation prior to drying resulted in sheets with better final mechanical properties than sheets made from pulp that had first been dried and then surface carboxymethylated.
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| 2. |
- 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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| 3. |
- Ankerfors, Mikael, et al.
(författare)
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Multilayer assembly onto pulp fibres using oppositely charged microfibrillated celluloses, starches, and wetstrength resins : Effect on mechanical properties of CTMP-sheets
- 2016
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Ingår i: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 31:1, s. 135-141
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Tidskriftsartikel (refereegranskat)abstract
- The effects of multilayering of microfibrillar cellulose (MFC) onto a chemi-thermomechanical pulp (CTMP), from which the fines material had been removed, were investigated with regard to the mechanical properties of hand-sheets. In one series of experiments, the CTMP was multilayered with cationic MFC/anionic MFC (C-MFC/A-MFC) at various addition levels and sheets made in a conventional sheet former, pressed, and dried at room temperature. This experimental series was complemented with a second series, where sheets were made in a Rapid Köthen sheet former. In a third series of experiments, the CTMP was multilayered using a cationic polyamideamine epichlorohydrine resin (PAE) and an AMFC. Sheets were formed using the Rapid Köthen sheet former. Finally, in a fourth series of experiments, the MFC multilayering experiments were compared with multilayering experiments using cationic starch/anionic starch (C-starch/A-Starch). MFC-multilayering (C-MFC/A-MFC) gave inferior strength gain at a low addition level compared to starch multilayering, but (compared on a weight basis) the strength seemed to level off using starches at high addition levels, whereas there were a continuous increase in strength using MFC multilayering. Multilayering using PAE/A-MFC was found to give a higher strength gain than both C-MFC/A-MFC and C-starch/A-starch multilayering. Sheet density was slightly affected (<14%) by the multilayering techniques used in these experiments.
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| 4. |
- Ankerfors, Mikael, et al.
(författare)
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The effects of different types of wet-end added microfibrillated celluloses on the properties of paper made from bleached kraft pulp
- 2017
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Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 32:3, s. 336-345
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Tidskriftsartikel (refereegranskat)abstract
- Research has been undertaken to compare the effects of different types of microfibrillated cellulose (MFC) on the mechanical properties of paper. Three types of MFC were produced: Enzyme MFC (low anionic charge density), Carboxymethylated MFC (high anionic charge density) and cationic MFC (high cationic charge density). The different MFCs required different retention aid strategies. The simplest retention strategy was selected to secure a high retention of MFC. Some experiments also focused on dewatering and pressability of wet webs with carboxymethylated MFC. Conventional isotropic laboratory handsheets were made using a never-dried unrefined elemental chlorine free (ECF)-bleached softwood kraft pulp. It has been shown that the evolution of the mechanical properties and scattering coefficients when plotted versus MFC content was very similar for the three types. However, Enzyme MFC gave a significantly better reinforcement effect. All three types of MFC had a similar effect on the sheet consolidation, reflected in sheet density. Evaluation of the dewatering and pressability of the wet sheets showed that if the MFC was aggregated by an appropriate retention strategy, the dewatering and pressability were not detrimental to the practical applicability of MFC.
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| 5. |
- 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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| 6. |
- Lindström, Tom, et al.
(författare)
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Nanoclay plating of cellulosic fiber surfaces
- 2008
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Ingår i: Journal of Applied Polymer Science. - : Wiley. - 0021-8995 .- 1097-4628. ; 108:2, s. 887-891
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Tidskriftsartikel (refereegranskat)abstract
- A basic problem in making cellulose-reinforced composites is achieving a dispersion of cellulosic fibers in an often olephinic polymer matrix. Drying cellulosic fibers results in the formation of fiber flocs/nodules because of their strong interfiber bonding, and this makes the hydrophilic cellulosic fibers difficult to disperse in a hydrophobic matrix material. One common approach to alleviate floe formation is to adsorb cationic surfactant onto anionically charged cellulose, which reduces the interfiber bonding, decreases floe formation and gives better compatibility with the matrix. In this report, a different approach is taken, namely to adsorb nanoclays onto the cellulosic fibers, and thereby reduce the natural hydrogen-bonding affinity between fibers. In a second report, the same technology will be shown to be advantageous to decrease floe formation in oleophinic composites reinforced with cellulosic fibers. This article summarizes experiments aimed at optimizing the chemistry of deposition of montmorillonite clay onto fiber surfaces. The aim was to optimize the chemical conditions for the heterodeposition of the anionic clay onto cationically charged fluff pulp. The experiments were designed to provide a theoretical framework for the deposition of the nanoclay onto the pulp fibers. High Mw p-DADMAC and an exfoliated clay (achieved by passing the clay through a homogenizer) were used. As expected, a certain degree of charge overcompensation by adding an electrolyte was necessary to bring about deposition. The adsorbed amount of clay could be calculated from the charge balance between the overcompensated charge and the net clay charge, constituting the theoretical framework for nanoclay heterodeposition. As expected, montmorillonite clay greatly destroyed the joint strength between fibers (determined by evaluating the strength of paper made from treated fibers). The surface coverage (determined by ESCA) was shown to be a linear function of the attached amount of clay, and ∌3% clay was required to fully cover the fiber surfaces. © 2008 Wiley Periodicals, Inc.
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| 7. |
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| 8. |
- Lindström, Tom, et al.
(författare)
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On the nature of joint strength of paper : Effect of dry strength agents - Revisiting the Page equation
- 2016
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Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 31:3, s. 459-468
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Tidskriftsartikel (refereegranskat)abstract
- This report deals with the effects of various chemical-treatments - carboxymethylcellulose-grafted (CMC) pulp in different ionic forms (Na+, Ca2+, and Al3+), cationic starch, anionic polyacrylamide, and microfibrillated cellulose (MFC) as well as PFI-refining on the strength properties of never-dried bleached soft-wood kraft pulp. The general in-plane strength properties were measured together with z-strength and interlaminar shear strength. The sheet density was varied by pressing the wet sheets to various dry solids content. The relative bonded area of the sheets was determined by the BET surface area of the sheets using krypton adsorption. Interlaminar shear strength is introduced as a measure for fibre-fibre bond strength and validates its use in the Page equation from first principles and it was shown to hold over a large range of tensile strengths. Only at very high tensile index values the calculated tensile index deviated from measured tensile index. This was most likely due to a shift from adhesive to cohesive failure of the joint. The various strength reinforcement methods used were all based on carbohydrate based additives and for those additives the specific joint strength was found to be independent of the specific additive, so the strength reinforcement is only related to the increased relative bonded area upon the addition of the strength adjuvant, although the additives consolidate the sheet on various structural levels.
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| 9. |
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