| 1. |
- Gimåker, Magnus, et al.
(författare)
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Influence of beating and chemical additives on residual stresses in paper
- 2011
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Ingår i: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 26:4, s. 445-451
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Tidskriftsartikel (refereegranskat)abstract
- Residual stresses are the stresses remaining in a material when all external forces are removed. Residual stresses in paper can influence the converting and end-use performance. There are well-established methods for determining residual stresses in paper, and some knowledge exists of how to control and tailor the residual stresses. However, there is an increasing demand to be able to tailor paper grades with respect to their mechanical properties. Pulp fibres are commonly beaten to improve the mechanical performance, but beating also increases the sheet density, de-watering resistance, and residual stresses of the paper produced. This work examines whether beating and the addition of chemical additives, i.e., a single layer of poly(allylamine) or a multilayer of poly(allylamine) and poly(acrylic acid), exert different effects on the build-up of residual stresses in paper. Both beating the fibres and adding polyelectrolytes increased the in-plane strength, stiffness, and residual stresses of the paper sheets prepared. The fact that the residual stresses did not scale linearly with the stiffness of the prepared sheets suggests that both beating and polyelectrolyte addition made the fibre/fibre joints transfer load at a lower solids content, such that stresses were transferred between fibre layers in the sheet earlier in the drying process, thus increasing the residual stresses. The fact that the strength gain when building polyelectrolyte multilayers induced less residual stresses than when the strength was increased by beating indicates the possibilities for producing paper with high strength but less residual stress.
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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, 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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| 4. |
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| 5. |
- Gimåker, Magnus, et al.
(författare)
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Adsorption of polyallylamine to lignocellulosic fibres : effect of adsorption conditions on localisation of adsorbed polyelectrolyte and mechanical properties of resulting paper sheets
- 2009
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Ingår i: Cellulose. - : Springer Netherlands. - 0969-0239 .- 1572-882X. ; 16:1, s. 87-101
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Tidskriftsartikel (refereegranskat)abstract
- Cationic polyallylamine (PAH), was adsorbed onto lignocellulosic fibres, and a fluorescent label on the polyelectrolyte enabled its location to be shown by confocal fluorescence microscopy. The adsorption time and ionic strength were varied to study their effect on the localisation of the adsorbed PAH. The microscopy showed that a long adsorption time, 24 h, and a high ionic strength, 10(-1) M NaCl + 5 x 10(-3) M NaHCO3 or higher, resulted in the adsorption of polyallylamine throughout the fibre walls. Shorter adsorption times and/or lower ionic strength resulted in adsorption only to the fibre exterior. By preparing sheets from fibres with polyelectrolyte adsorbed either to the exterior parts or into the fibre cell wall and testing their mechanical behaviour, a link was established between the localisation of adsorbed polyelectrolyte and the mechanical properties. Adsorption to the fibre exterior led to an increase in tensile strength and strain at break. The creep deformation at 90%RH was also slightly reduced by the adsorption of low molecular weight PAH (15 kDa). When polyallylamine was adsorbed throughout the wall of the lignocellulosic fibres, the mechanical properties were not however improved and the creep deformation at 90%RH actually increased somewhat.
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| 6. |
- Gimåker, Magnus, et al.
(författare)
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Graphite materials – Production from biomass?
- 2021
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Graphite materials show high electrical and thermal conductivity making them useful in electronics both as electrical conductor, but as of today primarily used as a thermal conductor for thermal management and as the dominating anode material in lithium ion batteries. The conductivities depend on for example the degree of graphitisation, that is how close the material is to perfect graphite. Graphite materials can occur naturally in the earth’s bedrock and can thus be extracted by mining and is then called natural graphite. Graphitic carbon materials can also be synthesised and are then usually referred to a synthetic or artificial graphite, even though they should be referred to as graphite materials if being strict, as they never reach the structure of perfect graphite and always contain some defects and irregularities. This report starts with a short description of all carbon allotropes, i.e. structurally different forms of the same element due to how the atoms are chemically bonded to each other. It then continues with an overview of how graphitic carbon materials can and should be characterised, as well as analytical methods for making this characterisation. After this a section on production methods for graphite materials follows, that dependent on the principles they operate by are divided into: • Mining for graphite that occurs naturally in the earth’s bedrock. • High temperature heat-treatment, so called carbonisation, hydrothermal carbonisation if done in water, and graphitisation. • Chemical vapour deposition, i.e. depositing molecules or atoms in gas phase on a solid surface, that is used to synthesise pyrolytic carbon and graphite. • Extraction from a steelmaking by-product called Kish to obtain so called Kish graphite. • Thermal decomposition of carbides. This is followed by a section on the today most common and important graphite materials, which are: natural graphite (mined), anisotropic synthetic graphite, isotropic synthetic graphite, pyrolytic carbon and graphite. This section also includes specific production process details for the above listed graphite materials, their main properties, advantages, and common uses. Two of the most common and important uses of graphite materials, i.e. as anode in lithium ion batteries and for thermal management in electronics, are described somewhat more in depth. The focus of this report is biomass derived graphitic materials and this focus start fully first in section number four, which compares published values on electrical and thermal conductivity of different fossil and bio-based graphitic carbon materials. This comparison clearly shows that it is very challenging to derive graphitic carbon materials with high conductivities from biomass. This is because essentially all biomass is so-called non-graphitising or hard carbon precursor meaning that it is not transformed into highly graphitic carbon no matter how high temperature it is heated to. Catalytic graphitisation using metals salts or oxides can increase the degree of graphitisation that can be achieved, but all substances used for catalysing graphitisation forms solid nanoparticles which leaves voids when removed by for example acid dissolution, making the resulting graphitic material porous which in turn limits its electrical and thermal conductivity. Of all production processes reviewed here to create highly electrically and thermally conductive graphitic carbon materials from biomass, requiring a high degree of graphitisation and dense material, two methods stand out as especially interesting: • Chemical vapour deposition on suitable substrate (carbon materials, metals or ceramics) using biomass as carbon source. • Resistive heating of biomass derived films/objects. Bio-based free-standing graphene film with very high electrical and thermal conductivity have been produced using chemical vapour deposition technique. From a practical handling perspective, it would be beneficial to create thicker highly graphitic carbon films to make them stronger, although it may reduce the conductivities of the material. Methods based on chemical vapour deposition may be improved to be able to produce thicker graphitic films. Resistive heating of a film made of e.g. biobased lignin, mixed with mined graphene to 2192 °C have been shown to create a highly graphitic carbon film with the excellent electrical conductivity of 4480 S/cm. By substituting the mined graphene to bio-based ditto may open up for the production of a fully biobased, highly graphitic film with excellent conductive properties. It is suggested that the way to achieve fully biobased highly graphitic and dense films is to further refine the chemical vapour deposition and the resistive heating method.
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| 7. |
- Gimåker, Magnus
(författare)
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Influence of adsorbed polyelectrolytes and adsorption conditions on creep properties of paper sheets made from unbleached kraft pulp
- 2007
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Papper uppvisar betydande tidsberoende mekaniska egenskaper som krypning och spänningsrelaxation. Det är känt att krypningen hos pappret påverkar till exempel en wellpapplådas förmåga att bära last under lång tid. En möjlighet att tillverka papper som kryper långsammare är därför önskvärd. Polyelektrolyter används ofta för att öka styrkan hos papper, och skulle kanske också kunna användas till att minska papprets krypning. Inverkan av polymera additiv på pappers krypegenskaper är emellertid knapphändigt beskrivet i litteraturen. Existerande studier har visat att polymera additiv inte påverkar krypningen hos starka papper och att fiberväggarna och fiber/fiber fogarna har fundamentalt olika betydelse för krypegenskaperna. Avsikten med denna avhandling var att undersöka hur adsorberade polyelektrolyter påverkar krypegenskaperna hos pappret. Ett av huvudsyftena var att studera om adsorptionen av en katjonisk polyelektrolyt – polyallylamin – endast till fiberytan eller tvärs hela fiberväggen ger olika effekt på krypningen hos papper tillverkade av dessa fibrer. En ny teknik där polyelektrolyten märks med en fluorescerande markör gör det möjligt att visualisera var i fibern de adsorberade molekylerna befinner sig. Resultaten visar att adsorption vid låg jonstyrka under kort tid bara ger adsorption till de yttre delarna av fiberväggen. Hög jonstyrka och lång adsorptions tid resulterar å andra sidan i adsorption tvärs hela fiberväggen. Med hjälp av denna teknik blev det också möjligt att klarlägga vilken inverkan polyelektrolytens läge i fiberväggen har på de slutgiltiga arkens mekaniska egenskaper. Krypprovning av de tillverkade arken visade tydligt att polyallylamin som endast adsorberat till fibrernas yttre delar minskade krypningen vid både 50 % och 90 % relativ luftfuktighet. Den uppnådda effekten visade sig dock bero på vilken typ av fibrer arken tillverkades av. Adsorption av katjoniserad stärkelse till fibrernas yta gav ingen nämnvärd effekt på arkens krypegenskaper, detta trots att stärkelse gav lika hög arkstyrka som polyallylamin. När polyallylamin adsorberades tvärs igenom fibrerväggen ökade krypningen vid 90 % relativ luftfuktighet väsentligt. Detta föreslås bero på att den adsorberade polyelektrolyten avsväller fibrerna vilket ger färre fiber/fiber kontakter och därmed en sämre fördelning av mekanisk last i arken. Det var emellertid inte möjligt att dra några definitiva slutsatser angående mekanismerna bakom de observerade skillnaderna i krypegenskaper.
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| 8. |
- Gimåker, Magnus, 1980-
(författare)
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Influence of fibre modification on moisture sorption and the mechanical properties of paper
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fibre modification might be a way to improve the performance of paper, to increase its cost competiveness and enable new paper-based products to be developed. Therefore, the influence of fibre modification (with polyelectrolytes or by fibre cross-linking) on the mechanical properties of special importance for packaging paper grades was studied. Creep deformation under varying humidity conditions (i.e. mechano-sorptive creep) is of outmost importance for the stacking life of paper-based boxes. The influence on creep behaviour of adsorbing polyallylamine (a cationic polyelectrolyte) to fibre surfaces or throughout the fibre walls was studied. Adsorption to fibre surfaces reduced the creep at constant humidity. The mechano-sorptive creep was not however influenced. The use of polyelectrolytes did not thus appear to be a feasible strategy for reducing mechano-sorptive creep. Polyelectrolytes can however be efficient in improving other mechanical properties. The use of multilayers consisting of polyallylamine (PAH) and polyacrylic acid (PAA) was for example shown to significantly increase the strength of paper with much less densification and build-up of residual stress than is obtained by beating. Cross-linking by oxidation with periodate radically decreased the mechano-sorptive creep of sheets made from the oxidised fibres. The basic mechanism behind the reduction in mechano-sorptive with cross-linking was found to be that the cross-linking slowed down the moisture sorption kinetics. A lower sorption rate led to smaller moisture content variations during the mechano-sorptive creep testing, and thus less sorption-induced swelling and stress concentrations at fibre/fibre joints. However, for cross-linking to be a practical way to reduce creep, the large problem of embrittlement must be solved. The shear strength of couched sheets was measured to study the interaction between the sheets at different solids content. The shear strength was low until a solids content of approximately 60−70% was reached, which suggests that interactions important for the strength at complete dryness start to develop at this solids content. The effect of different fibre modifications and additives on how the fibres interact during the consolidation process is not always well understood. The method of shear strength determination could in the future be applied to modified fibres to hopefully increase the understanding of how different modifications influence the fibre/fibre interactions. A deeper understanding might reduce the time for the development of new and improved fibre modifications.
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| 9. |
- Gimåker, Magnus, et al.
(författare)
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Influence of polymeric additives on short-time creep of paper
- 2007
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Ingår i: Nordic Pulp and Paper Research Journal. - 0283-2631. ; 22:2, s. 217-227
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Tidskriftsartikel (refereegranskat)abstract
- Cationic polyallylamine (PAH) and cationic starch were adsorbed to unbleached softwood kraft pulp fibres in order to study the effect of these additives on the creep properties of the resulting paper sheets. For the fibres treated with PAH, the effect of molecular mass, adsorbed quantity and heat treatment of the prepared sheets at 160 degrees C was also studied. PAH was found to not influence the sheet density, whereas starch addition induced moderate densification. Both additives produced major improvements in dry strength measurements as stress and strain-at-break. PAH-treated sheets also showed a relatively small but statistically significant improvement in tensile stiffness, unlike starch-treated sheets in which the improvement was too small to be statistically significant. As expected. there was an inverse relationship between the adsorbed amount and the molecular mass of the PAH. However, for comparable adsorbed amounts, the molecular mass made no detectable difference to the mechanical properties. PAH was also labelled with fluorescein isothiocyanate and adsorbed to the pulp fibres. Examination of the fibres with a confocal scanning laser microscope revealed that the different molecular mass fractions adsorbed only to the exterior parts of the fibres (i.e. the molecules did not penetrate throughout the fibre wall). The creep behaviour of the paper sheets was evaluated under tensile loading using a specially designed testing apparatus, in both 50% RH and 90% RH at 23 degrees C. Strain was monitored as function of time and applied load. PAH was found to lower both instantaneous and time-dependent deformation during the relatively short measuring time of 100 seconds used in this work. Cationic starch had little or no effect on creep. Thus it is clearly demonstrated that PAH treatment of fibres results in sheets with a lower creeping tendency over short periods compared to sheets made with non-treated and starch-treated fibres.
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| 10. |
- Gimåker, Magnus, et al.
(författare)
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On The Mechanisms Of Mechano-Sorptive Creep Reduction By Chemical Cross-Linking
- 2009
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Ingår i: Advances in Pulp and Paper Research, Oxford 2009. - Lancashire, UK : The Pulp and Paper Fundamental Research Society. - 9780954527266 ; , s. 1001-1017
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Konferensbidrag (refereegranskat)abstract
- Despite the technical importance of mechano-sorptive creep in paper, the exact mechanism behind this phenomenon is still not fully understood. In this study it was shown that the mechano-sorptive creep of paper sheets can be significantly reduced by chemical cross-linking through periodate oxidation. The mechanism behind this reduction has been examined through creep measurements of both sheets and individual fibres. For sheets the creep acceleration due to varying humidity was significantly reduced by the chemical cross-linking. For single fibres, however, the creep acceleration was not affected by the chemical crosslinking. In fact the absolute creep rate for the periodate oxidised fibres were higher than that of the reference fibres. This clearly showed that the improvement in mechano-sorptive creep found on a sheet level does not originate from an improved creep resistance for individual fibres but rather from mechanisms operating at the fibre network level. Hygroexpansion and moisture sorption of the sheets during the humidity cycling used for creep testing have also been measured, and the results showed that both was reduced by the periodate oxidation. Reduced moisture sorptivity and hygroexpansion probably minimises stress concentrations at the fibre network level and thereby also the creep acceleration.
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