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  • 1.
    Alimadadi, Majid
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kemiteknik.
    Foam-formed Fiber Networks: Manufacturing, Characterization, and Numerical Modeling: With a Note on the Orientation Behavior of Rod-like Particles in Newtonian Fluids2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Fiber networks are ubiquitous and are seen in both industrial materials (paper and nonwovens) and biological materials (plant cells and animal tissues). Nature intricately manipulates these network structures by varying their density, aggregation, and fiber orientation to create a variety of functionalities.

    In conventional papermaking, fibrous materials are dispersed in water to form a sheet of a highly oriented two-dimensional (2D) network. In such a structure, the in-plane mechanical and transport properties are very different from those in the out-of-plane direction. A three-dimensional (3D) network, however, may offer unique properties not seen in conventional paper products.

    Foam, i.e., a dispersed system of gas and liquid, is widely used as the suspending medium in different industries. Recently, foam forming was studied extensively to develop the understanding of foam-fiber interactions in order to find potential applications of this technology in papermaking.

    In this thesis, a method for producing low-density, 3D fiber networks by utilizing foam forming is investigated and the structures and mechanical properties of such networks are studied. Micro-computed tomography is used to capture the 3D structure of the network and subsequently to reproduce artificial networks. The finite element method is utilized to model the compression behavior of both the reproduced physical network and the artificial networks in order to understand how the geometry and constitutive elements of the foam-formed network affect its bulk mechanical properties. Additionally, a method was studied in order to quantify the orientation behavior of particles in a laminar Newtonian flow based on the key parameters of the flow which control the orientation.

    The resulting foam-formed structures were extremely bulky. Yet despite this high bulk, the fiber networks retained good structural integrity. The compression behavior in the thickness direction was characterized by extreme compressibility and high strain recovery after compression. The results from the modeling showed that the finite-deformation mechanical response of the fiber network in compression was satisfactorily captured by the simulation. However, the artificial network shows higher stiffness than the simulated physical network and the experiment. This discrepancy in stiffness was attributed to macroscopic structural non-uniformities in the physical network, which result in increased local compliance. It was also found that the friction between the fibers, as well as the fiber curvature, had a negligible impact on the compression response of the fiber network, while defects (in the form of kinks) had an effect on the response in the last stages of compression. The study of the orientation behavior of particles at different flow velocities, particle sizes, and channel geometries suggests that it might be possible to utilize the flow shear rate as a means to quantify the orientation behavior.

  • 2.
    Alimadadi, Majid
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Lindström, Stefan B.
    Division of Solid Mechanics, Department of Management and Engineering, Linköping University, Linköping, Sweden.
    Kulachenko, Artem
    Department of Solid Mechanics, Royal Institute of Technology (KTH), Stockholm, Sweden.
    Role of microstructures in the compression response of three-dimensional foam-formed wood fiber networks2018Inngår i: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 14, nr 44, s. 8945-8955, artikkel-id C7SM02561KArtikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High-porosity, three-dimensional wood fiber networks made by foam forming present experimentally accessible instances of hierarchically structured, athermal fiber networks. We investigate the large deformation compression behavior of these networks using fiber-resolved finite element analyses to elucidate the role of microstructures in the mechanical response to compression. Three-dimensional network structures are acquired using micro-computed tomography and subsequent skeletonization into a Euclidean graph representation. By using a fitting procedure to the geometrical graph data, we are able to identify nine independent statistical parameters needed for the regeneration of artificial networks with the observed statistics. The compression response of these artificially generated networks and the physical network is then investigated using implicit finite element analysis. A direct comparison of the simulation results from the reconstructed and artificial network reveals remarkable differences already in the elastic region. These can neither be fully explained by density scaling, the size effect nor the boundary conditions. The only factor which provides the consistent explanation of the observed difference is the density and fiber orientation nonuniformities; these contribute to strain-localization so that the network becomes more compliant than expected for statistically uniform microstructures. We also demonstrate that the experimentally manifested strain-stiffening of such networks is due to development of new inter-fiber contacts during compression.

  • 3.
    Alimadadi, Majid
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kemiteknik.
    Uesaka, Tetsu
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kemiteknik.
    3D-oriented fiber networks made by foam forming2016Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, ISSN 1572-882X, Vol. 23, nr 1, s. 661-671Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In industrial applications, such as paper and nonwovens, cellulose fibers are used in the form of a network where the fibers are oriented more or less in the sheet-plane direction. However, in many biological systems, fibers are instead oriented in a three-dimensional (3D) space, creating a wide variety of functionalities. In this study we created a 3D-oriented fiber network on the laboratory scale and have identified some unique features of its structure and mechanical properties. The 3D fiber network sheets were prepared by using foam-forming as well as modifying consolidation and drying procedures. The fiber orientation and tensile/compression behavior were determined. The resulting sheets were extremely bulky (above 190 cm3/g) and had extremely low stiffness (or high softness) compared to the reference handsheets. Despite this high bulk, the sheets retained good structural integrity. We found that a 3D-oriented fiber network requires much less fiber-fiber contact to create a connected (“percolated”) network than a two-dimensionally oriented network. The compression behavior in the thickness direction was also unique, characterized by extreme compressibility because of its extreme bulk and a long initial increase in the compression load as well as high strain recovery after compression because of its fiber reorientation during compression.

  • 4.
    Alimadadi, Majid
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kemiteknik.
    Uesaka, Tetsu
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kemiteknik.
    Exploring One-more Dimension of Paper: Properties of 3D-Orieneted Fiber Network2014Inngår i: Progress in Paper Physics Proceedings 2014, 2014Konferansepaper (Annet vitenskapelig)
  • 5.
    Alimohammadzadeh, Rana
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Osong, Sinke H.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kemiteknik.
    Dahlström, Christina
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kemiteknik.
    Cordova, Armando
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Scalable Improvement of the Strength Properties of Chemimechanical Pulp Fibers by Eco-Friendly Catalysis2018Inngår i: IMPC 2018, Trondheim, Norway, 2018Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The sustainable improvement of the strength properties of chemimechanical pulp by eco-friendlycatalysis is disclosed. Significant research activities have been performed on the use of cationic starchand polyelectrolyte complexes for improving the strength properties of cellulose-based materials. Herewe apply an eco-friendly strategy based on catalysis for significantly improving the strength propertiesof sheets made from chemimechanical pulp (CTMP) and bleeched sulphite pulp (BSP) using sustainablepolyelectrolyte complexes as the strength additives and organocatalysis. This surface engineeringstrategy significantly increased the strength properties of the assembled sheets (up to 100% in the caseof Z-strength). We also developed a catalytic selective colour marking of the cationic potato starch (CS)and carboxymethylcellulose (CMC) in order to elucidated how the specific strength additives aredistributed on the sheets. It revealed that the strength additives were more evenly distributed on thesheets made from CTMP as compared to BSP sheets. This is most likely attributed to the presence oflignin in the former lignocellulosic material. It also contributes to the increase in strength (up to 100%,Z-strength) for the CTMP derived sheets. The selective colour marking method also revealed that morestrength additives had been bound to the pulps in the presence of the catalyst.

  • 6. Andersen, A.
    et al.
    Örtegren, Jonas
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Koelsch, P.
    Wantke, D.
    Motschmann, H.
    Oscillating Bubble SHG on Surface Elastic and Surface Viscoelastic Systems: New Insights in the Dynamics of Adsorption Layers2006Inngår i: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 110, nr 37, s. 18466-18472Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Surface rheology governs a great variety of interfacial phenomena such as foams or emulsions and plays a dominant role in several technological processes such as high-speed coating. Its major difference with bulk rheology resides in the high compressibility of the surface phase, which is the direct consequence of the molecular exchange between adsorbed and dissolved species. In analogy to bulk rheology, a complex surface dilational modulus, ε, which captures surface tension changes upon defined area changes of the surface layer, can be defined. The module ε is complex, and the molecular interpretation of the dissipative process that gives rise to the imaginary part of the module is subject to some controversy. In this contribution, we used the oscillating bubble technique to study the surface dilational modulus in the mid-frequency range. The dynamic state of the surface layer was monitored by a pressure sensor and by surface second-harmonic generation (SHG). The pressure sensor measures the real and imaginary part of the modulus while SHG monitors independently the surface composition under dynamic conditions. The experiment allows the assessment of the contribution of the compositional term to the surface dilational modulus ε. Two aqueous surfactant solutions have been characterized:  a surface elastic and a surface viscoelastic solution. The elastic surface layer can be described within the framework of the extended Lucassen−van den Tempel Hansen model. The change in surface concentration is in phase with the relative area change of the surface layer, which is in strong contrast with the results obtained from the surface viscoelastic solution. Here, surface tension, area change, and surface composition are phase-shifted, providing evidence for a nonequilibrium state within the surface phase. The data are used to assess existing surface rheology models.

  • 7.
    Andersson, Henrik
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Manuilskiy, Anatoliy
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Gao, Jinlan
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Lidenmark, Cecilia
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Sidén, Johan
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Forsberg, Sven
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Unander, Tomas
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion. Dewire AB, Sundsvall 85185, Sweden.
    Nilsson, Hans-Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Investigation of Humidity Sensor Effect in Silver Nanoparticle Ink Sensors Printed on Paper2014Inngår i: IEEE Sensors Journal, ISSN 1530-437X, E-ISSN 1558-1748, Vol. 14, nr 3, s. Art. no. 6615915-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Thin inkjet-printed tracks of silver nanoparticles have previously been observed to show a non-reversible decrease in resistance when exposed to a high degree of relative humidity and thus providing sensor functionality with a memory effect. This paper provides a more in-depth explanation of the observed humidity sensor effect that originates from inkjet-printed silver nanoparticle sensors on a paper substrate. It is shown that the geometry of the sensor has a large effect on the sensor's initial resistance, and therefore also on the sensor's resistive dynamic range. The importance of the sensor geometry is believed to be due to the amount of solvent from the ink interacting with the coating of the paper substrate, which in turn enables the diffusion of salts from the paper coating into the ink and thus affecting the silver ink.

  • 8.
    Andersson, Kerstin
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Pranovich, Andrey
    Norgren, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Eriksson, Marie
    Holmbom, Bjarne
    Effects of biological treatment on the chemical structure of dissolved lignin-related substances in effluent from thermomechanical pulping2008Inngår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 23, nr 2, s. 164-171Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Effluent from a TMP-based pulp and paper mill was collected at the inlet and outlet of the mill's biological treatment plant and fractionated by sorption on XAD-8 resin and MTBE precipitation. Fractionation indicated that the refractory dissolved organic material in biologically treated effluent was mainly composed of lignin-related substances. Characterisation of the lignin-related substances by chromatographic and spectrometric methods confirmed the similarities of the isolated material and milled wood lignin. Fractionation and characterisation of alkali-extracted material from solids (biosludge) in biologically treated effluent found evidence of lignin-related material. Results indicated that biological treatment had altered the chemical structure and molar-mass distribution of dissolved lignin-related substances.

  • 9.
    Andersson, Matthias
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Norberg, Ole
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Kruse, Björn
    The substrate influence on colour measurement2003Inngår i: IS&T'S NIP19: INTERNATIONAL CONFERENCE ON DIGITAL PRINTING TECHNOLOGIES, 2003, s. 565-569Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The repeatable quality of color image reproduction is a growing challenge for producers of digital printing devices as well as for paper producers. The complex nature of the problem is due to the large number of factors that influence the quality. The properties of the printing substrate such as whiteness, gloss and surface roughness, the colorants and the printing procedure in different combinations together with the proper-ties of the capturing device are all factors that make objective evaluation of print quality very difficult. It is therefore imperative to develop precise methods and routines for color measurement and characterization. In this presentation, the influence of substrate properties on the final printed result will be studied by means of a flatbed digital scanner. The presentation will describe the problems associated with the influence of substrate properties on scanner calibration and will give guidelines for the use of scanners, where large-scale color management control is required. The work reported here is part of an ongoing development of a set of characterization procedures that can be applied to printing situations, consisting of a variety of different printing engines and papers.

  • 10.
    Andersson, Mattias
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Digital camera calibration for color measurements on prints2007Inngår i: Proceedings of SPIE - The International Society for Optical Engineering, SPIE - International Society for Optical Engineering, 2007, Vol. 6493, artikkel-id 64930TKonferansepaper (Fagfellevurdert)
    Abstract [en]

    Papers with a slightly blue shade are, at least among a majority of observers, perceived as whiter than papers having a more neutral color. Therefore, practically all commercially available printing papers contain bluish dyes and fluorescent whitening agents (FWA) to give the paper a whiter appearance. Furthermore, in the Paper Industry, the most frequently used measure for paper whiteness is the CIE-whiteness. The CIE Whiteness formula, does in turn, also favor slightly bluish papers. Excessive examples of high CIE-whiteness values can be observed in the office-paper segment where a high CIE-whiteness value is an important sales argument. As an effect of the FWA, spectrophotometer measurements of optical properties such as paper whiteness are sensitive to the ultraviolet (UV) content of the light source used in the instrument. To address this, the standard spectrophotometers used in the Paper Industry are equipped with an adjustable filter for calibrating the UV-content of the illumination. In the Paper Industry, spectrophotometers with d/0 measurement geometry and a light source of type C are used. The Graphic Arts Industry on the other hand, typically measures with spectrophotometers having 45/0 geometry and a light source of type A. Moreover, these instruments have only limited possibilities to adjust the UV-content by the use of different weighting filters. The standard for color measurements in the Paper Industry governs that measurements should be carried out using D65 standard illumination and the 10 degrees standard observer. The corresponding standard for the Graphic Arts Industry specify D50 standard illumination and the 2 degrees standard observer. In both cases, the standard illuminants are simulated from the original light source by spectral weighting functions. However, the activation of FWA, which will impact the measured spectral reflectance, depends on the actual UV-content of the illumination used. Therefore, comparisons between measurements on substrates containing FWA from two instruments having light sources with different UV-content are complicated. In this study, the effect of FWA content in paper on color reproduction has been quantified for an office-type paper. Furthermore, examples are given on how color measurement instruments give different readings when FWA is present. For the purpose of this study and in order to ensure that only the effect of FWA was observed, a set of papers with varying additions of FWA but otherwise identical, were produced on a small-scale experimental paper machine. The pilot papers were printed in three different printers. Two spectrophotometers representative to the instruments used in the Graphic Arts Industry and the Paper Industry respectively where used to measure the printed papers. The results demonstrate how the use of spectral weighting functions for simulating standard illuminants works properly on non-fluorescent material. However, when FWA is present, disparities in UV content between the light source and the simulated illuminant will result in color differences. Finally, in many printing processes, some of the used inks are UV-blocking, which further complicates the effect of FWA in printed material. An example is shown on how different color differences are obtained for different process ink combinations when the amount of FWA added to the paper is varied.

  • 11.
    Andersson, Mattias
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Norberg, Ole
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Color measurements on prints containing fluorescent whitening agents2007Inngår i: Proceedings of SPIE - The International Society for Optical Engineering, SPIE - International Society for Optical Engineering, 2007, Vol. 6493, s. Q4930-Q4950, artikkel-id 64930QKonferansepaper (Fagfellevurdert)
    Abstract [en]

    Papers with a slightly blue shade are, at least among a majority of observers, perceived as whiter than papers having a more neutral color. Therefore, practically all commercially available printing papers contain bluish dyes and fluorescent whitening agents (FWA) to give the paper a whiter appearance. Furthermore, in the Paper Industry, the most frequently used measure for paper whiteness is the CIE-whiteness. The CIE Whiteness formula, does in turn, also favor slightly bluish papers. Excessive examples of high CIE-whiteness values can be observed in the office-paper segment where a high CIE-whiteness value is an important sales argument. As an effect of the FWA, spectrophotometer measurements of optical properties such as paper whiteness are sensitive to the ultraviolet (UV) content of the light source used in the instrument. To address this, the standard spectrophotometers used in the Paper Industry are equipped with an adjustable filter for calibrating the UV-content of the illumination. In the Paper Industry, spectrophotometers with d/0 measurement geometry and a light source of type C are used. The Graphic Arts Industry on the other hand, typically measures with spectrophotometers having 45/0 geometry and a light source of type A. Moreover, these instruments have only limited possibilities to adjust the UV-content by the use of different weighting filters. The standard for color measurements in the Paper Industry governs that measurements should be carried out using D65 standard illumination and the 10 degrees standard observer. The corresponding standard for the Graphic Arts Industry specify D50 standard illumination and the 2 degrees standard observer. In both cases, the standard illuminants are simulated from the original light source by spectral weighting functions. However, the activation of FWA, which will impact the measured spectral reflectance, depends on the actual UV-content of the illumination used. Therefore, comparisons between measurements on substrates containing FWA from two instruments having light sources with different UV-content are complicated. In this study, the effect of FWA content in paper on color reproduction has been quantified for an office-type paper. Furthermore, examples are given on how color measurement instruments give different readings when FWA is present. For the purpose of this study and in order to ensure that only the effect of FWA was observed, a set of papers with varying additions of FWA but otherwise identical, were produced on a small-scale experimental paper machine. The pilot papers were printed in three different printers. Two spectrophotometers representative to the instruments used in the Graphic Arts Industry and the Paper Industry respectively where used to measure the printed papers. The results demonstrate how the use of spectral weighting functions for simulating standard illuminants works properly on non-fluorescent material. However, when FWA is present, disparities in UV content between the light source and the simulated illuminant will result in color differences. Finally, in many printing processes, some of the used inks are UV-blocking, which further complicates the effect of FWA in printed material. An example is shown on how different color differences are obtained for different process ink combinations when the amount of FWA added to the paper is varied.

  • 12. Andersson, Nina
    et al.
    Alberius, Peter
    Örtegren, Jonas
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Lindgren, Mikael
    Bergström, Lennart
    Photochromic mesostructured silica pigments dispersed in latex films2005Inngår i: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 25, s. 3507-3513Artikkel i tidsskrift (Fagfellevurdert)
  • 13.
    Andersson, Stefan
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Low consistency refining of mechanical pulp: process conditions and energy efficiency2011Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The thesis is focussed on low consistency (LC) refining of mechanical pulp. Theresearch included evaluations of energy efficiency, development of pulpproperties, the influence of fibre concentration on LC refining and effects of rotorposition in a two-zoned LC refiner.

    Trials were made in mill scale in a modern TMP line equipped with an MSDImpressafiner for chip pre-treatment, double disc (DD) first stage refining and aprototype 72-inch TwinFlo LC refiner in the second stage. Tensile index increasedby 8 Nm/g and fibre length was reduced by 10 % in LC refining at 140 kWh/adtgross specific refining energy and specific edge load 1.0 J/m. Specific lightscattering coefficient did not develop significantly over the LC refiner.

    The above mentioned TMP line was compared with a two stage single disc highconsistency Twin 60 refiner line. The purpose was to evaluate specific energyconsumption and pulp properties. The two different process solutions were testedin mill scale, running similar Norway spruce wood supply. At the same tensileindex and freeness, the specific energy consumption was 400 kWh/adt lower in theDD-LC concept compared with the SD-SD system. Pulp characteristics of the tworefining concepts were compared at tensile index 47 Nm/g. Fibre length was lowerafter DD-LC refining than after SD-SD refining. Specific light scattering coefficientwas higher and shive content much lower for DD-LC pulp.

    The effects of sulphite chip pre-treatment on second stage LC refining were alsoevaluated. No apparent differences in fibre properties after LC refining werenoticed between treated and untreated pulps. Sulphite chip pre-treatment iniiicombination with LC refining in second stage, yielded a pulp without screeningand reject refining with tensile index and shives content that were similar to nonpre-treated final pulp after screening and reject refining.

    A pilot scale study was performed to investigate the influence of fibreconcentration on pulp properties in LC refining of mechanical pulps. MarketCTMP was utilised in all trials and fibre concentrations were controlled by meansof adjustments of the pulp consistency and by screen fractionation of the pulp. Inaddition, various refiner parameters were studied, such as no-load, gap and baredge length. Pulp with the highest fibre concentration supported a larger refinergap than pulp with low fibre concentration at a given gross power input. Fibreshortening was lower and tensile index increase was higher for long fibre enrichedpulp. The results from this study support the interesting concept of combiningmain line LC refining and screening, where screen reject is recycled to the LCrefiner inlet.

    It has been observed that the rotor in two-zoned refiners is not always centred,even though pulp flow rate is equal in both refining zones. This leads to unequalplate gaps, which renders unevenly refined pulp. Trials were performed in millscale, using the 72-inch TwinFlo, to investigate differences in pulp properties androtor positions by means of altering the pressure difference between the refiningzones. In order to produce homogenous pulp, it was found that uneven plate gapscan be compensated for in LC refiners with dual refining zones. Results from thedifferent flow rate adjustments indicated that the control setting with similar plategap gave the most homogenous pulp.

  • 14.
    Andersson, Stefan
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för tillämpad naturvetenskap och design.
    Sandberg, Christer
    Holmen Paper AB, Braviken Paper Mill, SE-60188 Norrkoping, Sweden .
    Engstrand, Per
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för tillämpad naturvetenskap och design.
    Comparison of mechanical pulps from two stage HC single disc and HC double disc - LC refining2012Inngår i: Appita journal, ISSN 1038-6807, Vol. 65, nr 1, s. 57-62Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A mechanical pulping line consisting of high consistency (HC) double disc (DD) and low consistency (LC) refining was compared with a two stage single disc (SD) high consistency twin refiner line. The purpose of this study was to evaluate specific energy consumption and pulp properties. The two different process solutions were tested running similar Norway spruce wood supply. At similar tensile index and freeness, the DD-LC concept reduced the electric energy consumption by 400 kWh/adt compared with the traditional two-stage SD-SD system. Pulp characteristics of the two refining concepts were compared at tensile index 47 Nm/g. Fibre length was reduced more after DD-LC refining than after SD-SD refining. Specific light scattering coefficient was higher after DD-LC refining than SD-SD refining, while the development in second stage refining was better for SD-SD pulp than for DD-LC pulp. Shive level was significantly lower for DD-LC pulp than for SD-SD pulp.

  • 15.
    Andersson, Stefan
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Sandberg, Christer
    Engstrand, Per
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Effect of fibre length distribution on low consistency refining of mechanical pulpManuskript (preprint) (Annet vitenskapelig)
  • 16.
    Andersson, Stefan
    et al.
    Holmen Paper AB, Bravikens Pappersbruk, SE-601 88 Norrköping, Sweden.
    Sandberg, Christer
    Holmen Paper AB, Bravikens Pappersbruk, SE-601 88 Norrköping, Sweden.
    Engstrand, Per
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för tillämpad naturvetenskap och design.
    Effect of long fibre concentration on low consistency refining of mechanical pulp2012Inngår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, nr 4, s. 702-706Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The aim of this study was to investigate the influence of long fibre concentration on loadability and pulp properties during LC refining of mechanical pulp. Long fibre concentration was adjusted to three different levels by screen fractionation of the pulp. The three pulps were refined in a single disc pilot scale LC refiner at similar process conditions. Increased long fibre concentration supported a larger refiner gap and resulted in less fibre cutting at a given specific energy consumption. The higher long fibre concentration probably contributed to a stronger fibre network that maintained a larger refining gap at certain specific energy consumption. Increased long fibre concentration also enabled a higher tensile index increase in the LC refiner at certain fibre length reduction. The study supports a process combining LC refining with screen fractionation, where the long fibre fraction is recycled to the refiner feed. This enables a higher loadability and a more effective utilisation of the LC refiner. By using this technology, overall specific energy consumption can be reduced if a larger share of the refining is performed in LC rather than HC refining.

  • 17.
    Andersson, Stefan
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Sandberg, Christer
    Engstrand, Per
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    The effect of rotor position on pulp properties in a two-zoned low consistency refiner2012Inngår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, nr 3, s. 525-530Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Earlier studies have shown that plate gaps are sometimes unequal in two-zoned low consistency refiners and that unequal gaps render unevenly refined pulp. It is also known that optimisation of plate gap in low consistency refining leads to improved energy efficiency. In this work, trials were made in mill scale in a modern TMP line equipped with a prototype 72 inch TwinFlo low consistency refiner in second stage. The study was designed to investigate the development of pulp properties from different rotor positions by means of altering the outlet flow rate ratio. The specific energy consumption was calculated for each refining zone and setting, based on flow rate and temperature increase. In order to produce homogenous pulp, it was found that uneven plate gaps need to be compensated in low consistency refiners with dual refining zones. Results from the different flow rate adjustments indicated that the control setting with similar plate gap gave the most homogenous pulp. However, further studies are needed to find an adequate rotor control strategy. The temperature increase in each refining zone seems to correlate well with the applied specific energy consumption in each refining zone.

  • 18. Andreasson, B
    et al.
    Forsström, Jennie
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Wågberg, Lars
    Determination of fibre pore structure: influence of salt, pH and conventional wet strength resins2005Inngår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 12, nr 3, s. 253-265Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    It has been shown, in the present investigation, that the two methods used to investigate the pore size distribution of unbleached chemical pulps, i.e. inverse size exclusion chromatography (ISEC) and nuclear magnetic resonance (NMR), give different average pore radius for the pores inside the fibre wall. This is due to the way in which these experiments are performed and the sensitivity of the methods to different types of pores in the cell wall. It was also shown that the two methods gave different results when changing the pH and the ionic strength of the pulp suspension. The pore radius, as detected with ISEC, decreased with both increasing ionic strength and decreasing pH, indicating a loose structure of the exterior of the fibrillar network. However, the pore radius as detected with NMR, was virtually unaffected when increasing the ionic strength, indicating a very rigid structure of the interior of the fibre wall. Decreasing pH though, lead to a decrease in pore radius indicating that upon protonation of the carboxylic groups in the fibre wall, the electrostatic repulsion is diminished and the average pore radius decreases. The NMR technique was also used to study wet strength aid penetration into the fibre wall. It was shown that wet strength aids with a small molecular weight, penetrated the fibre wall, as detected by a decrease in pore radius. It was also shown that addition of different wet strength aids increased the tensile index of the sheet and decreased the fibre strength, measured as zero span-strength of the sheets.

  • 19.
    Ashraf, Shakeel
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Mattsson, Claes
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Fondell, Mattis
    Helmholtz Zentrum, Inst Methods & Instrumentat Synchrotron Radiat Re, Berlin, Germany.
    Lindblad, Andreas
    Uppsala Univ, Dept Chem, Angstrom Lab, Uppsala, Sweden.
    Thungström, Göran
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Surface modification of SU-8 for metal/SU-8 adhesion using RF plasma treatment for application in thermopile detectors2015Inngår i: Materials Research Express, ISSN 2053-1591, Vol. 2, nr 8, artikkel-id 086501Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This article reports on plasma treatment of SU-8 epoxy in order to enhance adhesive strength for metals. Its samples were fabricated on standard silicon wafers and treated with (O2 & Ar) RF plasma at a power of 25W at a low pressure of (3×10-3 torr) for different time spans (10 sec – 70 sec). The sample surfaces were characterized in terms of contact angle, surface (roughness and chemistry) and using a tape test. During the contact angle measurement, it was observed that the contact angle was reduced from 73° to 5° (almost wet) and 23° for (O2 & Ar) treated samples, respectively. The RMS surface roughness was significantly increased by 21.5% and 37.2% for (O2 & Ar) treatment, respectively. A pattern of metal squares was formed on the samples using photolithography for a tape test. An adhesive tape was applied to the samples and peeled off at 180o. The maximum adhesion results, more than 90%, were achieved for the O2-treated samples, whereas the Ar-treated samples showed no change. The XPS study shows the formation of new species in the O2-treated sample compared to the Ar-treated samples. The high adhesive results were due to the formation of hydrophilic groups and new O2 species in the O2-treated samples, which were absent in Ar-treated samples.

  • 20.
    Bayat, Nazlin
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Carlberg, Torbjörn
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Influence of Heat Treatment on the Surface Structure of 6082 Al Alloys2017Inngår i: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 48A, nr 10, s. 5085-5094Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    The β-Al5FeSi intermetallic phase and coarse Mg2Si particles have negative effects on extrudability and workability of 6xxx Al alloys billets. To achieve extruded products with a high surface quality, the as-cast billets are heat-treated before extrusion. During heat treatment, the undesired intermetallic particles, i.e., β-AlFeSi platelets are transformed to rounded α-Al(FeMn)Si intermetallic phases. Although the heat treatment of the bulk areas of the 6xxx Al alloys has been the focus of many previous studies, the process of phase transformation at the very surface has not been paid the same attention. In this study, microstructures of a homogenized billet of a 6082 alloy at the area very close to the surface were investigated. By comparing the X-ray diffraction patterns (XRD) of heat-treated samples as a function of different holding times, the gradual phase transformations could be followed, and using GDOES and map analysis by EDX, the alloying elemental redistribution was analyzed. Partial remelting and porosity growth was detected, and transformation rates were faster than in bulk material and from what is known from industrial processes.

  • 21.
    Bayat, Nazlin
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Carlberg, Torbjörn
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Surface structure formation in direct chill (DC) casting of al alloys2014Inngår i: JOM: The Member Journal of TMS, ISSN 1047-4838, E-ISSN 1543-1851, Vol. 66, nr 5, s. 700-710Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The aim of this study is to increase the understanding of the surface zone formation during direct chill (DC) casting of aluminum billets produced by the air slip technology. The depth of the shell zone, with compositions deviating from the bulk, is of large importance for the subsequent extrusion productivity and quality of final products. The surface microstructures of 6060 and 6005 aluminum alloys in three different surface appearances - defect free, wavy surface, and spot defects - were studied. The surface microstructures and outer appearance, segregation depth, and phase formation were investigated for the mentioned cases. The results were discussed and explained based on the exudation of liquid metal through the mushy zone and the fact that the exudated liquid is contained within a surface oxide skin. Outward solidification in the surface layer was quantitatively analyzed, and the oxide skin movements explained meniscus line formation. Phases forming at different positions in the segregation zone were analyzed and coupled to a cellular solidification in the exudated layer.

  • 22.
    Bayat, Nazlin
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Carlberg, Torbjörn
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Cieslar, M.
    Faculty of Mathematic and Physics, Charles University, Prague, Czech Republic.
    In-Situ Study of Phase Transformations during Homogenization of 6005 and 6082 Al Alloys2017Inngår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 725, s. 504-509Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Intermetallic β-Al5FeSi phase and coarse Mg2Si particles have negative effects on extrudability and workability of 6xxx Al alloy billets. To achieve extruded products with a high surface quality as-cast billets are therefore heat-treated before extrusion. During heat treatment the undesired intermetallic particles, i.e., β-AlFeSi platelets, are transformed to a rounded α-Al(FeMn)Si intermetallic phase. This transformation was studied in-situ by TEM for 6005 and 6082 Al alloys. It was observed that the Mg2Si particles precipitate in the Al matrix at about 250 °C; this precipitation also occurred at the edge and faces of beta intermetallic particles, and the Mg2Si particles were the preferred sites for α-Al(FeMn)Si particle nucleation. The transformation proceeded faster and at lower temperatures, 350–450 °C, than what has been reported earlier for homogenization studies of bulk samples and industrial billets. This could be associated with the thin characteristic of used samples in TEM giving contribution from fast surface diffusion, but it was also concluded that the phase boundary layer diffusion was important for the understanding of how the transformations proceed.

  • 23.
    Bayat, Nazlin
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Carlberg, Torbjörn
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Cieslar, M.
    Charles University, Prague, Czech Republic.
    In-Situ Study of Phase Transformations during Homogenization of 6060 and 6063 Al Alloys2019Inngår i: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 130, s. 165-171Artikkel i tidsskrift (Fagfellevurdert)
  • 24.
    Bergström, David
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik och hållbar utveckling.
    The Absorption of Laser Light by Rough Metal Surfaces2008Doktoravhandling, med artikler (Annet vitenskapelig)
  • 25.
    Bergström, David
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    The reflectance of steels and non-ferrous alloys: 2nd Pacific International Conference on Application of Lasers and Optics 20062006Inngår i: PICALO 2006 - 2nd Pacific International Conference on Applications of Laser and Optics - Conference Proceedings, 2006, s. 140-145Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    The measurement of reflectance is important for the analysis and modelling of laser-material interactions. Unfortunately, most of the reflectance data presently available consider only polished pure metals rather than the commercially available (unpolished, oxidised) alloys which are actually being processed. This paper presents the results of reflectance measurements carried out on as-received engineering grade metals including: hot and cold rolled mild steel, zinc coated mild steel, stainless steel, aluminium alloys, copper and brass. The measurements were made using an integrating sphere with an Nd:YLF laser at two wavelengths (1053 nm and 527 nm). The results obtained differ considerably from existing data for polished, pure metals and should help to improve the accuracy of laser-material interaction models.

  • 26.
    Bergström, David
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Kaplan, AFH
    Powell, J
    Light scattering and absorption in Gaussian random rough metal surfaces using the geometric optics approximation2007Inngår i: 20th Meeting on Mathematical Modelling of Material Processing with Lasers, 2007Konferansepaper (Fagfellevurdert)
  • 27.
    Bergström, David
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik och hållbar utveckling.
    Kaplan, AFH
    Powell, J
    The absorption of light by rough metal surfaces - a three-dimensional ray-tracing analysis2008Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 103, nr 10, s. 103515-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The laser absorptance of rough surfaces has been investigated by using Monte Carlo simulations based on three-dimensional (3D) ray tracing. The influence of multiple scattering, shadowing, and the Fresnel-equation based angle dependence is discussed. The 3D results are compared to previously published results from a two-dimensional ray-tracing analysis and the different applications of the two models are explained.

  • 28.
    Bergström, David
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Kaplan, Alexander
    Mathematical Modelling of Laser Absorption Mechanisms in Metals: A Review2003Inngår i: M4PL16 - 16th Meeting on Mathematical Modelling of Materials Processing with Lasers, 2003Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    In Laser Material Processing, an understanding of the fundamental absorption mechanisms plays a vital role in determining the optimum processing parameters and conditions. To this end, a combination of experimental as well as of theoretical work is required. In this paper, results of some of the most important mathematical models of laser-metal interactions are reviewed, including models for absorptivity dependence on wavelength, polarization, angle of incidence, workpiece temperature, surface roughness, defects, impurities and oxides.

  • 29.
    Bergström, David
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Kaplan, Alexander
    Powell, J
    Laser absorption measurements in opaque solids2005Inngår i: 10th NOLAMP Conference : the 10th Nordic Laser Materials Processing Conference, 17-19 August 2005, Luleå Sweden, Luleå: Luleå University of Technology , 2005, s. 444-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In LaserMaterial Processing, an understanding of the fundamental absorption mechanisms plays a vital role in determining the optimum processing parameters and conditions. The absorptance, which characterizes how much a material absorbs, can alter during a processing application, as a result of melting, boiling, structural changes of the surface, oxidation, plasma formation, etc. To gain knowledge of these complex processes, a combination of experimental as well as of theoretical work is required. In this paper, an overview of the most common experimental methods and techniques to measure laser absorption in opaque solids, such as metals, will be presented.

  • 30.
    Bergström, David
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Powell, J.
    Kaplan, A. F. H.
    A ray-tracing analysis of the absorption of light by smooth and rough metal surfaces2007Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, nr 11, artikkel-id 113504Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ray tracing has been employed to investigate the absorption of light by smooth and random rough metal surfaces. For normally incident light the absorptance of the surface increases with surface roughness. However, for light incident at a tangent to the surface the absorptance-surface roughness relationship is more complex. For example, in certain cases the absorptance can rise, fall, and rise again as the surface roughness increases. In this paper this complex absorptance-roughness relationship is defined and explained. The wavelengths of the light chosen for this study correspond to the primary and secondary output wavelengths of Nd:YAG lasers.

  • 31.
    Bergström, David
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Powell, John
    Laser Expertise Ltd., Nottingham, United Kingdom.
    Kaplan, Alexander
    Luleå University of Technology.
    Absorptance of Non-Ferrous Alloys to Nd:YLF and Nd:YAG Laser Light at Room Temperature2007Inngår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 46, nr 8, s. 1290-1301Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The measurement of absorptance is important for the analysis and modelling of laser-material interactions. Unfortunately, most of the absorptance data presently available considers only polished pure metals rather than the commercially available (unpolished, oxidised) alloys which are actually being processed in manufacturing. This paper presents the results of absorptance measurements carried out at room temperature on as-received engineering grade non-ferrous metals (Al, Cu and Zn alloys). The measurements were made using an integrating sphere with an Nd:YLF laser at two wavelengths (1053nm and 527nm � which means that the results are also valid for Nd:YAG radiation at 1064nm and 532nm). The absorptance results obtained differ considerably from existing data for polished, pure metals and should help improve the accuracy of laser-material interaction models. Some clear trends were identified. For all 22 cases studied the absorptance was higher than for ideal pure, polished metals. For all Al- and Cu-samples the absorptance was higher for the green than it was for the infrared wavelength, while for all Zn-coatings this trend was reversed. No clear correlation between absorptance and surface roughness was found at low roughness values (Sa 0.15 � 0.60) but one, rougher set of samples (Sa 2.34), indicated a roughness-absorptance correlation at higher roughness levels.

  • 32.
    Bergström, David
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Powell, John
    Laser Expertise Ltd., Nottingham, United Kingdom.
    Kaplan, Alexander
    Luleå University of Technology.
    The absorptance of steels to Nd:YLF and Nd:YAG laser light at room temperature2007Inngår i: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 253, nr 11, s. 5017-5028Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The measurement of absorptance is important for the analysis and modelling of laser-material interactions. Unfortunately, most of the absorptance data presently available considers only polished pure metals rather than the commercially available (unpolished, oxidised) alloys, which are actually being processed in manufacturing. This paper presents the results of absorptance measurements carried out at room temperature on as-received engineering grade steels including hot and cold rolled mild steel and stainless steels of various types. The measurements were made using an integrating sphere with an Nd:YLF laser at two wavelengths (1053 and 527 nm, which means that the results are also valid for Nd:YAG radiation at 1064 and 532 nm). The absorptance results obtained differ considerably from existing data for polished, pure metals and should help improve the accuracy of laser-material interaction models. Some clear trends were identified; for all materials studied, the absorptance was considerably higher than the previously published values for the relevant pure metals with polished surfaces. For all 15 samples the absorptance was higher for the green than for the infrared wavelength. No clear trend correlating the absorptance with the roughness was found for mild steel in the roughness range Sa 0.4-5.6 μm. A correlation between absorptance and roughness was noted for stainless steel for Sa values above 1.5 μm.

  • 33.
    Björk, Elisabeth
    et al.
    RISE - Research Institutes of Sweden, Bioekonomi.
    Bouveng, Mikael
    RISE - Research Institutes of Sweden, Bioekonomi.
    Vomhoff, Hannes
    Holmen AB.
    Fines-enriched pulp as a strength agent in a CTMP middle ply2018Inngår i: PaperCon 2018: Shaping the future through innovation, TAPPI Press, 2018, artikkel-id PA5.2Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The objective of this pilot scale trial, was to evaluate fines-enriched pulp (FE-pulp) as a strength agent in amiddle ply of a board product.A typical CTMP-based middle ply was produced on the FEX pilot paper machine. The stock consisted of CTMP,refined hardwood and softwood pulp, and filler. FE-pulp as strength agent was compared with glue pulp, ahighly refined chemical pulp. FEX sheets and hand sheets made of pulp mixtures were evaluated. Also, thedewatering and pressing conditions on the paper machine were compared.The results confirmed the results of earlier experiments with handsheets; FE-pulp used as strength agent showedto be twice as efficient as glue pulp regarding strength properties without impairing the bulk. Further, thedewatering conditions and press dryness's on the paper machine was comparable at these additions. Thus, allthese results imply that addition of FE-pulp can replace the double amount of glue pulp as a strength agent.

  • 34.
    Björk, Elisabeth
    et al.
    RISE - Research Institutes of Sweden, Bioekonomi.
    Bouveng, Mikael
    RISE - Research Institutes of Sweden, Bioekonomi.
    Vomhoff, Hannes
    Holmen AB.
    Production of pulps with an extremely high fines content for use as strength agent2018Inngår i: PaperCon 2018: Shaping the future through innovation, TAPPI Press, 2018, artikkel-id PA5.1Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The objective was to optimize the production of fines-enriched pulp (FE-pulp) from chemical pulp.The first trial was a continuous production of FE-pulp with unbleached and bleached never-dried softwood. Thepulp was refined using a JC00 equipped with SF filling, and screened with a micro-perforated screen basket with250 μm diameter holes, but the produced FE-pulp got low concentration, below 3 g/l.The second trial aimed at optimised conditions, using dried bleached softwood. Three fillings, microbar, AA andFF were evaluated in a JC01 refiner, where microbar was most energy efficient. Microbar and AA reachedtargeted FE-pulp concentration, 10 g/l. The refined pulps were screened with different hole diameters, where, asexpected, larger hole diameters resulted in higher concentration but also lower fines content in the FE-pulps.The last trial, the microbar filling was evaluated for never-dried softwood pulp, unbleached and bleached. Now,the refining of unbleached softwood gave 3 times more fines per kWh/ton compared with first trial.These trials demonstrated the importance of the right refining conditions regarding effect of refiner and type offilling to achieve glue-pulp with high enough fines content. With the right conditions, it was possible to produceFE-pulp with high concentration at moderate energy consumption.

  • 35.
    Blomquist, Nicklas
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap. STT Emtec AB, Sundsvall.
    Wells, Thomas
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Andres, Britta
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Bäckström, Joakim
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Forsberg, Sven
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Olin, Håkan
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Metal-free supercapacitor with aqueous electrolyte and low-cost carbon materials2017Inngår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, artikkel-id 39836Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Electric double-layer capacitors (EDLCs) or supercapacitors (SCs) are fast energy storage devices with high pulse efficiency and superior cyclability, which makes them useful in various applications including electronics, vehicles and grids. Aqueous SCs are considered to be more environmentally friendly than those based on organic electrolytes. Because of the corrosive nature of the aqueous environment, however, expensive electrochemically stable materials are needed for the current collectors and electrodes in aqueous SCs. This results in high costs for a given energy-storage capacity. To address this, we developed a novel low-cost aqueous SC using graphite foil as the current collector and a mix of graphene, nanographite, simple water-purification carbons and nanocellulose as electrodes. The electrodes were coated directly onto the graphite foil by using casting frames and the SCs were assembled in a pouch cell design. With this approach, we achieved a material cost reduction of greater than 90% while maintaining approximately one-half of the specific capacitance of a commercial unit, thus demonstrating that the proposed SC can be an environmentally friendly, low-cost alternative to conventional SCs.

  • 36.
    Bohlin, Erik
    et al.
    Karlstad Universitet.
    Gustafsson Coppel, Ludovic
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Johansson, Caisa
    Karlstads Universitet.
    Edström, Per
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Modelling of brightness decrease in coated cartonboard as an effect of calendering: Microroughness and effective refractive index aspects2010Inngår i: 11th Advanced Coating Fundamentals Symposium Proceedings: The Latest Advances in Coating Research and Development, Norcross, GA, USA: TAPPI Press, 2010, s. 51-65Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Calendering of coated paper leads to a brightness decrease. The mechanism for this is not clear, although it has been discussed in the past. One common explanation is that the porosity of the coating layer decreases and hence scattering. By comparing simulated and measured results this paper shows that modifications of the surface properties account for the brightness decrease of GCC coated substrates with calendering. The effect of a deformable cartonboard substrate is investigated here and compared to a less deformable plastic film substrate. From simulations based on a two-layer Kubelka-Munk model, it is shown that the brightness decrease of the cartonboard due to calendering has a negligible contribution to the brightness decrease of the coated cartonboard. The brightness decrease was similar for coated plastic film and coated cartonboard. The thickness of GCC coated plastic films was not affected by calendering irrespectively of the pigment and latex size distribution. Monte Carlo light scattering simulations, taking into account the measured decrease of surface microroughness and increased effective refractive index, showed that surface modifications accounted for most of the observed brightness decrease of the GCC coated substrate, whereas the bulk scattering and absorption coefficients were not affected by calendering. It is also shown that the scattering coefficient is significantly dependent on the coat weight whereas the physical absorption coefficient is not.

  • 37.
    Botero, Carlos Alberto
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kvalitets- och maskinteknik.
    Koptyug, Andrey
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kvalitets- och maskinteknik.
    Jiménez-Piqué, Emilio
    Universitat Politècnica de Catalunya, Barcelona, Spain.
    Rännar, Lars-Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kvalitets- och maskinteknik.
    Microstructure and nanomechanical behavior of modified 316L-based materials fabricated using EBM2018Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Stainless steel 316L based materials modified by the additions of iron-based wear-resistant alloys (Colferoloy@ 103 and 139) used for thermal spray coatings applications were fabricated by EBM. Process parameters were tailored to fabricate compact specimens of 1cm3 in an Arcam A2 (Arcam AB, Mölndal, Sweden) at Mid Sweden University. Microstructural features of the materials obtained were characterized by OM and SEM in polished and etched samples. Nanoindentation tests carried out at different penetration depths were performed on selected areas of the polished specimens to evaluate the materials micro/nano mechanical behavior and to establish correlations with the observed microstructure.

  • 38.
    Botero Vega, Carlos Alberto
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kvalitets- och maskinteknik.
    Jiménez-Piqué, Emilio
    Universitat Politècnica de Catalunya, Barcelona.
    Roos, Stefan
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kvalitets- och maskinteknik.
    Skoglund, Per
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kvalitets- och maskinteknik.
    Koptioug, Andrei
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kvalitets- och maskinteknik.
    Rännar, Lars-Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kvalitets- och maskinteknik.
    Bäckström, Mikael
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kvalitets- och maskinteknik.
    Nanoindentation: a suitable tool in metal Additive Manufacturing2018Konferansepaper (Fagfellevurdert)
  • 39.
    Bujtar, Peter
    et al.
    Southern General Hospital, Glasgow.
    Simonovics, Janos
    Southern General Hospital, Glasgow.
    Koptyug, Andrey
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för ekoteknik och hållbart byggande.
    George, Sandor
    Southern General Hospital, Glasgow.
    Varadi, Karoly
    Southern General Hospital, Glasgow.
    Emerging manufacturing bioengineering technologies 2: Scaffold designing experiment using titanium scaffolds2014Inngår i: British Journal of Oral & Maxillofacial Surgery, ISSN 0266-4356, E-ISSN 1532-1940, Vol. 52, nr 8, s. e60-e61Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Substantial volume defects of the head and neck oftenrequire customized solutions to improve quality of life likefree flap transfers.Titanium and its alloys are versatile materialsproviding the feature of osteointegration. The conditionswhich facilitate the deposition of lamellar bone are underextensive research. Our project aimed to determine whethertitanium can function as a scaffold - unlike simple plates - toenhance bone regeneration for load bearing structures. Thereaction of stem cells to scaffolds with varying stiffness willbe presented.Additive manufacturing were used to produce a variety ofscaffolds to optimize titanium structures. Electric beam melting(EBM) manufacturing allowed us to optimize the elasticmodulus (Young) of the titanium to match with cadaveric 

    bone from a previous project. Multidirectional mechanicaltests were performed on the various designs of titanium cellstructures (n=80). The predictability and quality of manufacturingwas assessed statistically and also with scanningelectron microscope (SEM).The results demonstrated structures matching the mechanicalproperties of bone and even anisotropy as our resultssuggest 3GPa elasticity. This allows the possibility to buildregenerating bone with predictable properties. In addition,predictable patterning - unlike etching and sandblasting - ofmicroscopic (nano) features found to be significant and nonhomogenous simple repetitive patterns provide better cellularresponse.The benefit that tissue engineering techniques offer isdecreased morbidity, relative independence from donor site,with a highly specific and customized shape. Titanium basedreconstruction constructs seems to offer an alternative futurefor bony reconstruction.

  • 40. Bäckström, Marie
    et al.
    Hammar, Lars-Åke
    Htun, Myat
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Beatability and runnability studies of ion-exchanged unbleached kraft pulps on a pilot scale2009Inngår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 24, nr 1, s. 94-100Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    It has earlier been shown that the counter-ion to the charged groups in the fibre has a significant effect on the beatability of fibres, but large-scale investigations of this effect are scarce in the literature. The objectives of the present study were therefore to develop a technique to ion-exchange large quantities of industrial pulp into the Na+-form using complexing agents and to study the effect of industrial-scale refining on pulp fibres in the Na+-form and how the fibres respond to industrial-like papermaking. The results show that ion-exchange can indeed be conducted on a pilot-scale using complexing agents such as DTPA. The study further indicates that an energy reduction of 50% at a given WRV or tensile index may be achieved if the fibres are converted to Na+-form prior to pilot-scale refining. By applying these techniques in full-scale production, it should thus be possible to save significant amount of energy, especially in the case of papers made from unbleached pulp that usually demands a higher degree of beating to achieve sufficient strength.

  • 41.
    Carlberg, Torbjorn
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Jarfors, Anders E. W.
    School of Engineering, Jönköping University, 55111 Jönköping, Sweden .
    On Vertical Drag Defects Formation During Direct Chill (DC) Casting of Aluminum Billets2014Inngår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 45, nr 1, s. 175-181Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    During air-slip direct chill casting of aluminum billets, one of the major defects occurring includes traces along the billet called vertical drags (VDs). If the VDs are too deep or too many, then they cause scraping of the billets. As in the subsequent extrusion process, the surface quality is known to impair both the productivity and quality of the profiles. In cast-house practice, many theories circulate about the causes of VD defects and how to avoid them, but in the literature, no thorough treatments have been made to explain this phenomenon. In the current study, the outer appearance, structure around, and compositions at the defects are analyzed. A theory for the formation of the defects, their cause, and how their appearance is coupled to different alloy types is presented. The segregation in the vicinity of the defects is discussed based on deformation of semisolid materials and coupled to Reynolds dilatancy in granular materials. The theory can explain differences between 6063 and 6005 alloys.

  • 42.
    Carlberg, Torbjörn
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    A Review of Radial Segregation in Crystal Growth during Microgravity2006Inngår i: Progress in crystal growth and characterization of materials, ISSN 0960-8974, E-ISSN 1878-4208, Vol. 52, nr 3, s. 213-222Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    This review describes radial segregation results from crystal growth experiments in microgravity, together with their corre-sponding theoretical treatments. The paper is structured in terms of the different factors influencing radial segregation during crystal growth, such as: curved growth interfaces, variations in boundary layer thicknesses, weak convection, facets and magnetic fields. In a number of experiments considerably stronger radial segregation occurs in space than is normally observed on earth. The theoretical treatments lead to a sound understanding of all of the results. Possible ways to avoid the problem, such as the application of magnetic fields, are outlined.

  • 43.
    Carlberg, Torbjörn
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Experimental Study of Radial Segregation Caused by Weak Convection2005Inngår i: Microgravity, science and technology, ISSN 0938-0108, E-ISSN 1875-0494, Vol. 15, nr 1, s. 35-39Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Under conditions of weak convection in the liquid during metal solidification and crystal growth, large chemical inhomogeneities can occur due to insufficient mixing of the melt. In this project a series of experiments with increasing melt flow, driven by thermo-capillary forces, have been performed in a Get Away Special flight. The level of convection was evaluated quantitatively from analysis of axial segregation profiles. As expected a significantly stronger radial segregation has occurred in the space grown material compared to ground based reference experiments. It was also found that there was a shift of the position of maximum concentration when the flow was increased. Unexpected axial solute maxima were also revealed in the space samples. A comparison was made to numerical simulations, and good correlations were found to first order effects.

  • 44.
    Carlberg, Torbjörn
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Radial Segregation during Microgravity Experiments: Presented at The International Conference on Advances in Solidification Processing, Stockholm, Sweden, June 20052005Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Under conditions of weak convection in the liquid during metal solidification and crystal growth, large chemical inhomogeneities can occur due to insuffi-cient mixing of the melt. In this project a series of experiments with increasing melt flow, driven by thermo-capillary forces, have been performed in a Get Away Special flight. The level of convection was evaluated quanti-tatively from analysis of axial segregation profiles. As expected a significantly stronger radial segre-gation has occurred in the space grown mate-rial compared to ground based reference experiments. It was also found that there was a shift of the position of max-imum concentration when the flow was in-creased. Unexpected axial solute maxima were also revealed in the space samples. A comparison was made to numerical simulations, and good correla-tions were found to first order effects.

  • 45.
    Carlberg, Torbjörn
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Silicon crystal formation during DC casting of aluminium-silicon alloys2009Inngår i: TMS Light Metals 2009, Minerals, Metals & Materials Society, 2009, s. 837-841Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The formation of polyhedral silicon crystals in aluminium 7-8% silicon alloys has been studied in industrial ingots. It was found that the nucleation temperature and the cooling rate were important factors influencing the amount and size of the polyhedral crystals. To avoid large particles in the as cast material early nucleation have to be suppressed and the phosphorous content should be kept low. Modeling of diffusion-controlled growth of the silicon phase in this type of aluminium-silicon alloys shows how the nucleation temperature influences the morphology of the precipitated silicon.

  • 46.
    Carlberg, Torbjörn
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Silicon Particle Precipitation during DC Casting of Al-Si Clad Alloys2010Inngår i: Materials Science Forum, Trans Tech Publications Inc., 2010, s. 307-313Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The formation of polyhedral silicon crystals in aluminium 7-9% silicon alloys has been studied both in industrial ingots and in simulation experiments in a Bridgman furnace. It was found that the nucleation temperature and the cooling rate were important factors influencing the amount and size of the polyhedral crystals. To avoid large particles in the as cast material early nucleation have to be suppressed and the phosphorous content should be kept low. Modelling of diffusion-controlled growth of the silicon phase in this type of aluminium-silicon alloys shows how the nucleation temperature influences the morphology of the precipitated sili¬con.

  • 47.
    Carlberg, Torbjörn
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Bayat, Nazlin
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Erdegren, Mikael
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Surface Segregation and Surface Defect Formation During Aluminum Billet Casting2015Inngår i: Transactions of the Indian Institute of Metals, ISSN 0972-2815, E-ISSN 0975-1645, Vol. 68, nr 6, s. 1065-1069Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper the surface zone formation during direct chill casting of aluminum billets, produced by the air slip technology, is discussed. The shell zone depth and compositions have been quantitatively studied, and the surface microstructures of 6060, 6005 and 6082 alloys are compared and coupled to surface appearances. The understanding of the results is based on the exudation of liquid metal through the mushy zone and the fact that the exudate liquid is contained within a surface oxide skin, and the oxide skin movements are coupled to various surface appearances. The major defects that occur during billet castings are different kinds of vertical drags or horizontal bandings, also called lapping. The structures coupled to these defects and theories for their formation are discussed.

  • 48.
    Carlberg, Torbjörn
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Jaradeh, Majed
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Kamgou Kamga, H.
    Solidification Studies of Automotive Heat Exchanger Materials2006Inngår i: JOM: The Member Journal of TMS, ISSN 1047-4838, E-ISSN 1543-1851, Vol. 58, nr 11, s. 56-61Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Based on the aluminium alloy AA 3003 different modifications of that alloy family have been studied to improve and tailor the properties of the material for its applications in automotive heat exchangers. Laboratory techniques have been applied to simulate industrial DC-casting, together with some basic solidification studies. The results are coupled to structures observed in industrial size ingots and discussed in terms of structure property relations.

  • 49.
    Carlberg, Torbjörn
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Winkler, C.
    Amberg, G.
    Weak Convection Influencing Radial Segregation2000Inngår i: European Space Agency, (Special Publication) ESA SP, 2000, Vol. 454 I, s. 431-436Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    The influence of weak convection, caused by surface tension forces, on radial segregation occuring in crystals grown under microgravity conditions is studied in a project involving both numerical simulations and space experiments. The geometry studied is a Bridgman configuration with a partially coated surface. Small slots in the coating give free surface in a controlled way, and the free surface area is the parameter in the investigation. The experiments will be performed in a GAS module, which will be flown in the beginning of year 2001. The paper presents the experimental technique in detail as well as some results obtained during the development phase. Numerical simulations have been performed and results of how the radial segregation varies with the convection level will be presented. The project is the first phase of a research program, which will continue with experiments in the ISS.

  • 50.
    Carlsson, Peter
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Irreversibel termodynamik i trätorkningssammanhang1994Rapport (Annet vitenskapelig)
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