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  • 1.
    Alimadadi, Majid
    et al.
    Department of Natural Sciences, Mid Sweden University, Sweden.
    Lindström, Stefan B
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    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 networks2018In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 14, p. 8945-8955Article in journal (Refereed)
    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, weare 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.

  • 2.
    Andric, Jelena
    et al.
    Chalmers University of Technology.
    Fredriksson, Sam T.
    Chalmers University of Technology.
    Lindström, Stefan B
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Sasic, Srdjan
    Chalmers University of Technology.
    Nilsson, Håkan
    Chalmers University of Technology.
    A study of a flexible fiber model and its behavior in DNS of turbulent channel flow2013In: Acta Mechanica, ISSN 0001-5970, E-ISSN 1619-6937, Vol. 224, no 10, p. 2359-2374Article in journal (Refereed)
    Abstract [en]

    The dynamics of individual flexible fibers in a turbulent flow field have been analyzed, varying their initial position, density and length. A particle-level fiber model has been integrated into a general-purpose, open source computational fluid dynamics code. The fibers are modeled as chains of cylindrical segments connected by ball and socket joints. The equations of motion of the fibers contain the inertia of the segments, the contributions from hydrodynamic forces and torques, and the connectivity forces at the joints. Direct numerical simulation of the incompressible Navier-Stokes equations is used to describe the fluid flow in a plane channel, and a one-way coupling is considered between the fibers and the fluid phase. We investigate the translational motion of fibers by considering the mean square displacement of their trajectories. We find that the fiber motion is primarily governed by velocity correlations of the flow fluctuations. In addition, we show that there is a clear tendency of the thread-like fibers to evolve into complex geometrical configurations in a turbulent flow field, in fashion similar to random conformations of polymer strands subjected to thermal fluctuations in a suspension. Finally, we show that fiber inertia has a significant impact on reorientation timescales of fibers suspended in a turbulent flow field.

  • 3.
    Andric, Jelena
    et al.
    Chalmers University of Technology, Göteborg, Sweden.
    Lindström, Stefan B
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Sasic, Srdjan
    Chalmers University of Technology, Göteborg, Sweden.
    Nilsson, Håkan
    Chalmers University of Technology, Göteborg, Sweden.
    Rheological properties of dilute suspensions of rigid and flexible fibers2014In: Journal of Non-Newtonian Fluid Mechanics, ISSN 0377-0257, E-ISSN 1873-2631, Vol. 212, p. 36-46Article in journal (Refereed)
    Abstract [en]

    Particle-level simulations are used to study the rheology of monodispersed suspensions of rigid and flexible fibers in a creeping, simple shear flow of a Newtonian fluid. We also investigate the influence of different equilibrium shapes (straight and curved) of the fibers on the behavior of the suspension. A parametric study of the impacts of fiber flexural rigidity and morphology on rheology quantifies the effects of these realistic fiber features on the experimentally accessible rheological properties. A fiber is modeled as a chain of rigid cylindrical segments, interacting through a two-way coupling with the fluid described by the incompressible three-dimensional Navier–Stokes equations. The initial fiber configuration is in the flow–gradient plane. We show that, when the shear rate is increased, straight flexible fibers undergo a buckling transition, leading to the development of finite first and second normal stress differences and a reduction of the viscosity. These effects, triggered by shape fluctuations, are dissimilar to the effects induced by the curvature of stiff, curved fibers, for which the viscosity increases with the curvature of the fiber. An analysis of the orbital drift of fibers initially oriented at an angle to the flow–gradient plane provides an estimate for the time-scale within which the prediction of the rheological behavior is valid. The information obtained in this work can be used in the experimental characterization of fiber morphology and mechanics through rheology.

  • 4.
    Benselfelt, Tobias
    et al.
    Department of Fiber Technology, KTH, Stockholm, Sweden.
    Nordenström, Malin
    Department of Fiber Technology, KTH, Stockholm, Sweden.
    Lindström, Stefan B
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Wågberg, Lars
    Department of Fiber Technology, KTH, Stockholm, Sweden.
    Explaining the Exceptional Wet Integrity of Transparent Cellulose Nanofibril Films in the Presence of Multivalent Ions: Suitable Substrates for Biointerfaces2019In: Advanced Materials Interfaces, ISSN 2196-7350, Vol. 13, no 6, article id 1900333Article in journal (Refereed)
    Abstract [en]

    Cellulose nanofibrils (CNFs) assemble into water‐resilient materials in the presence of multivalent counter‐ions. The essential mechanisms behind these assemblies are ion–ion correlation and specific ion effects. A network model shows that the interfibril attraction indirectly influences the wet modulus by a fourth power relationship to the solidity of the network (Ew ∝ φ4). Ions that induce both ion–ion correlation and specific ion effects significantly reduce the swelling of the films, and due to the nonlinear relationship dramatically increase the wet modulus. Herein, this network model is used to explain the elastoplastic behavior of wet films of 2,2,6,6‐tetramethylpiperidine‐1‐oxyl radical (TEMPO)‐oxidized, carboxymethylated, and phosphorylated CNFs in the presence of different counter‐ions. The main findings are that the aspect ratio of the CNFs influences the ductility of the assemblies, that the bivalency of phosphorylate ligands probably limits the formation of interfibril complexes with divalent ions, and that a higher charge density increases the friction between fibrils by increasing the short‐range attraction from ion–ion correlation and specific ion effects. These findings can be used to rationally design CNF materials for a variety of applications where wet strength, ductility, and transparency are important, such as biomaterials or substrates for bioelectronics.

  • 5.
    Chen, Zhe
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Hörnqvist Colliander, Magnus
    Department of Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Sundell, Gustav
    Department of Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Zhou, Jinming
    Division of Production and Materials Engineering, Lund University, Sweden.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Nano-scale characterization of white layer in broached Inconel 7182017In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 684, p. 373-384Article in journal (Refereed)
    Abstract [sv]

    The formation mechanism of white layers during broaching and their mechanical properties are not well investigated and understood to date. In the present study, multiple advanced characterization techniques with nano-scale resolution, including transmission electron microscopy (TEM), transmission Kikuchi diffraction (TKD), atom probe tomography (APT) as well as nano-indentation, have been used to systematically examine the microstructural evolution and corresponding mechanical properties of a surface white layer formed when broaching the nickel-based superalloy Inconel 718.

    TEM observations showed that the broached white layer consists of nano-sized grains, mostly in the range of 20–50 nm. The crystallographic texture detected by TKD further revealed that the refined microstructure is primarily caused by strong shear deformation. Co-located Al-rich and Nb-rich fine clusters have been identified by APT, which are most likely to be γ′ and γ′′ clusters in a form of co-precipitates, where the clusters showed elongated and aligned appearance associated with the severe shearing history. The microstructural characteristics and crystallography of the broached white layer suggest that it was essentially formed by adiabatic shear localization in which the dominant metallurgical process is rotational dynamic recrystallization based on mechanically-driven subgrain rotations. The grain refinement within the white layer led to an increase of the surface nano-hardness by 14% and a reduction in elastic modulus by nearly 10% compared to that of the bulk material. This is primarily due to the greatly increased volume fraction of grain boundaries, when the grain size was reduced down to the nanoscale.

  • 6.
    Denoyelle, Thibaud
    et al.
    Solid Mechanics, KTH.
    Kulachenko, Artem
    Solid Mechanics, KTH.
    Galland, Sylvain
    Wallenberg Wood Science Center, KTH.
    Lindström, Stefan B
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Elastic properties of cellulose nanopaper versus conventional paper2011In: / [ed] Ulrich Hirn, Graz, Austria: TU , 2011, p. 131-134Conference paper (Other academic)
  • 7.
    Ekstrand, Eva-Maria
    Linköping University, Department of Thematic Studies, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences.
    Anaerobic digestion in the kraft pulp and paper industry: Challenges and possibilities for implementation2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The pulp and paper industry is a large producer of wastewater and sludge, putting high pressure on waste treatment. In addition, more rigorous environmental legislation for pollution control and demands to increase the use of renewable energy have put further pressure on the pulp and paper industry’s waste treatment, where anaerobic digestion (AD) and the production of methane could pose a solution. Kraft pulping makes up 80% of the world production of virgin wood pulp, thus, the wastewaters from this sector represent a large unused potential for methane production.

    There are three main types of substrates available for AD at pulp and paper mills, the wastewaters, the primary sludge/fibre sludge, and the waste activated sludge. AD treatment of these streams has been associated with several challenges, such as the presence of inhibiting compounds or low degradability during AD. The aim of this thesis was to experimentally address these challenges and potentials, focusing on wastes from kraft mills.

    Methane potential batch tests showed that many wastewater streams still posed challenges to AD, but the alkaline elemental chlorine-free bleaching stream and the condensate effluents had good methane potentials. Further, the methane potential of kraft mill fibre sludge was high, and co-digestion of kraft mill fibre sludge and waste activated sludge was feasible in stirred tank reactors with sludge recirculation. By increasing the organic loading in a pilot-scale activated sludge facility and thereby lowering the sludge age, the degradability of the waste activated sludge was improved. The higher wastewater treatment capacity achieved by this method provides an opportunity for the mills to increase their pulp and paper production. Further, by dewatering the digestate after AD and returning the liquid to the activated sludge treatment, costs for nutrient supplementation can be reduced.

    In conclusion, the thesis shows that AD of wastes from the kraft pulp and paper industry was feasible and carried many benefits regarding the generation of methane as a renewable energy carrier, improved wastewater treatment and reduced costs. Different strategies on how AD may be implemented in the kraft pulp and paper industry were formulated and discussed.

    List of papers
    1. Methane potentials of the Swedish pulp and paper industry - A screening of wastewater effluents
    Open this publication in new window or tab >>Methane potentials of the Swedish pulp and paper industry - A screening of wastewater effluents
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    2013 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 112, p. 507-517Article in journal (Refereed) Published
    Abstract [en]

    With the final aim of reducing the energy consumption and increase the methane production at Swedish pulp and paper mills, the methane potential of 62 wastewater effluents from 10 processes at seven pulp and/or paper mills (A-G) was determined in anaerobic batch digestion assays. This mapping is a first step towards an energy efficient and more sustainable utilization of the effluents by anaerobic digestion, and will be followed up by tests in lab-scale and pilot-scale reactors. Five of the mills produce kraft pulp (KP), one thermo-mechanical pulp (TMP), two chemical thermo-mechanical pulp (CTMP) and two neutral sulfite semi-chemical (NSSC) pulp. Both elementary and total chlorine free (ECF and TCF, respectively) bleaching processes were included. The effluents included material from wood rooms, cooking and oxygen delignification, bleaching (often both acid- and alkali effluents), drying and paper/board machinery as well as total effluents before and after sedimentation. The results from the screening showed a large variation in methane yields (percent of theoretical methane potential assuming 940 NmL CH4 per g TOC) among the effluents. For the KP-mills, methane yields above 50% were obtained for the cooking effluents from mills D and F, paper machine wastewater from mill D, condensate streams from mills B, E and F and the composite pre-sedimentation effluent from mill D. The acidic ECF-effluents were shown to be the most toxic to the AD-flora and also seemed to have a negative effect on the yields of composite effluents downstream while three of the alkaline ECF-bleaching effluents gave positive methane yields. ECF bleaching streams gave higher methane yields when hardwood was processed. All TCF-bleaching effluents at the KP mills gave similar degradation patterns with final yields of 10-15% of the theoretical methane potential for four of the five effluents. The composite effluents from the two NSSC-processes gave methane yields of 60% of the theoretical potential. The TMP mill (A) gave the best average yield with all six effluents ranging 40-65% of the theoretical potential. The three samples from the CTMP process at mill B showed potentials around 40% while three of the six effluents at mill G (CTMP) yielded 45-50%.

    Place, publisher, year, edition, pages
    Elsevier, 2013
    Keywords
    Biogas; Anaerobic digestion; Kraft pulp; Chemical thermo-mechanical pulp; Neutral sulfite semi-chemical pulp; Bleaching
    National Category
    Social Sciences
    Identifiers
    urn:nbn:se:liu:diva-104129 (URN)10.1016/j.apenergy.2012.12.072 (DOI)000329377800053 ()
    Available from: 2014-02-07 Created: 2014-02-07 Last updated: 2019-05-07
    2. High-rate anaerobic co-digestion of kraft mill fibre sludge and activated sludge by CSTRs with sludge recirculation
    Open this publication in new window or tab >>High-rate anaerobic co-digestion of kraft mill fibre sludge and activated sludge by CSTRs with sludge recirculation
    Show others...
    2016 (English)In: Waste Management, ISSN 0956-053X, E-ISSN 1879-2456, Vol. 56, p. 166-172Article in journal (Refereed) Published
    Abstract [en]

    Kraft fibre sludge from the pulp and paper industry constitutes a new, widely available substrate for thebiogas production industry, with high methane potential. In this study, anaerobic digestion of kraft fibresludge was examined by applying continuously stirred tank reactors (CSTR) with sludge recirculation.Two lab-scale reactors (4L) were run for 800 days, one on fibre sludge (R1), and the other on fibre sludgeand activated sludge (R2). Additions of Mg, K and S stabilized reactor performance. Furthermore, theCa:Mg ratio was important, and a stable process was achieved at a ratio below 16:1. Foaming was abatedby short but frequent mixing. Co-digestion of fibre sludge and activated sludge resulted in more robustconditions, and high-rate operation at stable conditions was achieved at an organic loading rate of 4 gvolatile solids (VS) L1 day1, a hydraulic retention time of 4 days and a methane production of230 ± 10 Nm L per g VS.

    Place, publisher, year, edition, pages
    Elsevier, 2016
    Keywords
    Pulp and paper Anaerobic digestion Sludge recirculation High-rate CSTR Fibre sludge Activated sludge
    National Category
    Renewable Bioenergy Research Production Engineering, Human Work Science and Ergonomics Production Engineering, Human Work Science and Ergonomics Water Engineering
    Identifiers
    urn:nbn:se:liu:diva-131780 (URN)10.1016/j.wasman.2016.06.034 (DOI)000383827700020 ()27453288 (PubMedID)
    Funder
    Swedish Energy Agency
    Note

    Funding agencies: Swedish Energy Agency [32802-1]; Scandinavian Biogas Fuels AB; Poyry AB; BillerudKorsnas AB; SCA; Fiskeby Board AB; Purac AB

    Available from: 2016-10-05 Created: 2016-10-05 Last updated: 2019-05-07Bibliographically approved
    3. Combining high-rate aerobic wastewater treatment with anaerobic digestion of waste activated sludge at a pulp and paper mill
    Open this publication in new window or tab >>Combining high-rate aerobic wastewater treatment with anaerobic digestion of waste activated sludge at a pulp and paper mill
    2018 (English)In: Water Science and Technology, ISSN 0273-1223, E-ISSN 1996-9732, Vol. 77, no 8, p. 2068-2076Article in journal (Refereed) Published
    Abstract [en]

    The activated sludge process within the pulp and paper industry is generally run to minimize the production of waste activated sludge (WAS), leading to high electricity costs from aeration and relatively large basin volumes. In this study, a pilot-scale activated sludge process was run to evaluate the concept of treating the wastewater at high rate with a low sludge age. Two 150 L containers were used, one for aeration and one for sedimentation and sludge return. The hydraulic retention time was decreased from 24 hours to 7 hours, and the sludge age was lowered from 12 days to 2–4 days. The methane potential of the WAS was evaluated using batch tests, as well as continuous anaerobic digestion (AD) in 4 L reactors in mesophilic and thermophilic conditions. Wastewater treatment capacity was increased almost four-fold at maintained degradation efficiency. The lower sludge age greatly improved the methane potential of the WAS in batch tests, reaching 170 NmL CH4/g VS at a sludge age of 2 days. In addition, the continuous AD showed a higher methane production at thermophilic conditions. Thus, the combination of high-rate wastewater treatment and AD of WAS is a promising option for the pulp and paper industry.

    Keywords
    Activated sludge, sludge age, anaerobic digestion, biochemical methane potential, CSTR, pulp and paper
    National Category
    Bioprocess Technology
    Identifiers
    urn:nbn:se:liu:diva-146089 (URN)10.2166/wst.2018.120 (DOI)000435663800011 ()29722692 (PubMedID)
    Note

    Funding agencies: Swedish Energy Agency [32802-2]; Scan-dinavian Biogas Fuels AB; Poyry AB; BillerudKorsnas AB; SCA; Fiskeby Board AB; Purac AB

    Available from: 2018-05-07 Created: 2018-05-07 Last updated: 2019-05-07Bibliographically approved
  • 8.
    Fall, Andreas B.
    et al.
    Department of Fiber Technology, KTH.
    Lindström, Stefan B
    Department of Fiber Technology, KTH.
    Sundman, Ola
    Department of Forest Products Technology, Aalto University, Aalto, Finland.
    Ödberg, Lars
    Department of Fiber Technology, KTH.
    Wågberg, Lars
    Department of Fiber Technology, KTH.
    Colloidal stability of aqueous nanofibrillated cellulose dispersions2011In: Langmuir, ISSN 0743-7463, Vol. 27, no 18, p. 11332-11338Article in journal (Refereed)
    Abstract [en]

    Cellulose nanofibrils constitute an attractive raw material for carbon neutral, biodegradable, nanostructured materials. In a aqueous suspensions, these nanofibrils are stabilized by electrostatic repulsion arising from deprotonated carboxyl groups at the fibril surface. In the present work, a new model is developed for colloidal stability by considering the deprotonation and electrostatic screening. This model predicts the fibril-fibril interaction potential in a given pH and ionic strength environment. Experiments support the model predictions that aggregation is induced by decreasing pH, thus reducing the surface charge, or by increasing salt concentration. It is shown that the primary aggregation mechanism for salt addition is the surface charge reduction through specific interactions of counter-ions with the deprotonated carboxyl groups, while the screening effect of the salt is of secondary importance.

  • 9.
    Fall, Andreas
    et al.
    Department of Fiber Technology, KTH.
    Lindström, Stefan B
    Department of Fiber Technology, KTH.
    Sprakel, Joris
    Löfroth, J. -E
    Wågberg, Lars
    Department of Fiber Technology, KTH.
    Shear-stiffening cellulose nanofiber gels with tuneable mechanical characteristics2011In: 241St National Meeting And Exposition Of The American Chemical Society (Acs), 2011, Vol. 241, p. 131--Conference paper (Refereed)
    Abstract [en]

    Gels have been synthesized from the renewable, strong and low cost cellulose nanofibres; nanofibrillated cellulose (NFC). The gels are shown to exhibit pronounced shear-stiffening properties and large extensibility (above 100%). The stiffening is due to strain induced orientation of the nanofibers, which is enabled by the free rotation at the particle-particle joints. The gels are synthesized from low concn. aq. NFC solns. By decreasing the electrostatic double-layer repulsion between the NFC fibrils, aggregation is initiated and a fluid-gel transition occurs. This transition can be detected within a range of vol. fractions. We characterize the gel microstructures using dynamic light scattering and the mech. properties using a rheometer. The mech. properties of these gels are tuneable; significantly different properties are seen if gels are formed by reducing pH or by increasing ionic strength. It is also obsd. that the properties of the gels depend on the type of counter-ion.

  • 10.
    Fenton, Paul David
    et al.
    Linköping University, Department of Management and Engineering, Environmental Technology and Management. Linköping University, Faculty of Science & Engineering.
    Hermelin, Brita
    Linköping University, Department for Studies of Social Change and Culture, Centre for Municipality Studies. Linköping University, Faculty of Arts and Sciences.
    Den attraktiva regionen: kommunens roll i nationella infrastruktur satsningar2015Conference paper (Refereed)
    Abstract [sv]

    Genom fallstudien av BanaVäg Motala-Mjölby undersöker detta paper hur kommunerna och lokala verksamheter genom planeringsinsatser, initiativ och samarbeten stärker effekterna och nyttan av tillgång till förstärkt fysisk infrastruktur för persontransporter. Studien avgränsas geografiskt till Motala och Mjölby centralorter, till Skänninge tätort, och till att belysa de lokalsamhälleliga effekterna. 

  • 11.
    Funkquist, John
    Linköping University, Department of Management and Engineering, Malmstens Linköping University.
    Att hitta och släppa kontroll: Hantverk i teori och praktik2019Independent thesis Basic level (degree of Bachelor), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [en]

    The aim of this thesis is to explore how theoretical studies on handicrafts may be rewarding and usefull for a craftsman. The aim is also to explore how quality is defined within crafts and to explore different aesthetic qualities that can be achieved within the craft of cabinetmaking. In addition, the aim is also to broaden the view on how skillfullnes may be expressed within the craft of cabinetmaking. The work begins with theoretical studies of two craft philosophers - David Pye and Soetsu Yanagi. Then, their ideas are applied practically through the making of two pieces of furniture. Aesthetic expressions characterized by randomness, imperfection and irregularity is specially sought after. The conclusions of the thesis shows that theoretical studies may be benefiting and rewarding for a craftsman.

  • 12.
    Holmvall, Martin
    et al.
    FSCN, Mid Sweden University.
    Drolet, Francois
    FPInnovations.
    Uesaka, Tetsu
    FSCN, Mid Sweden University.
    Lindström, Stefan B
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Microfluidics in printing nip-liquid transfer on random fiber network surface2011In: / [ed] Ulrich Hirn, Graz, Austria: TU , 2011, p. 67-68Conference paper (Other academic)
  • 13.
    Hämäläinen, J.
    et al.
    University of Technology, P.O, Lappeenranta, Finland .
    Lindström, Stefan B
    Department of Fiber Technology, KTH.
    Hämäläinen, T.
    University of Eastern Finland, P.O., Kuopio, Finland .
    Niskanen, H.
    University of Eastern Finland, P.O, Kuopio, Finland .
    Papermaking fiber suspension flow simulations at multiple scales2011In: Journal of Engineering Mathematics, ISSN 0022-0833, Vol. 71, no 1, p. 55-79Article in journal (Refereed)
    Abstract [en]

    Papermaking flows are extremely challenging for modeling and simulation, if one accepts their full complexity. A wide range of particles, including fibers, fiber fragments (fines) and fillers (non-organic particles), flow and interact with each other in a nondilute suspension, a complex geometry and at a high flow rate. Different simulation approaches are reviewed from particle-level simulations, through mesoscale simulations to the full flow geometry of the papermaking line. Their application to papermaking and potential to provide fundamental understanding as well as direct process-optimization support are discussed.

  • 14.
    Kulachenko, Artem
    et al.
    Solid Mechanics, KTH, Stockholm.
    Denoyelle, Thibaud
    Solid Mechanics, KTH, Stockholm.
    Galland, Sylvain
    Wallenberg Wood Science Centre, KTH, Stockholm.
    Lindström, Stefan B
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Elastic properties of cellulose nanopaper2012In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 19, no 3, p. 793-807Article in journal (Refereed)
    Abstract [en]

    Nanopaper is a transparent film made of network-forming nanocellulose fibers. These fibers are several micrometers long with a diameter of 4–50 nm. The reported elastic modulus of nanopaper often falls short of even conservative theoretical predictions based on the modulus of crystalline cellulose, although such predictions usually perform well for other fiber composite materials. We investigate this inconsistency and suggest explanations by identifying the critical factors affecting the stiffness of nanopaper. A similar inconsistency is found when predicting the stiffness of conventional paper, and it is usually explained by the effects introduced during drying. We found that the effect of the drying cannot solely explain the relatively low elastic modulus of nanopaper. Among the factors that showed the most influence are the presence of non-crystalline regions along the length of the nanofibers, initial strains and the three-dimensional structure of individual bonds

  • 15.
    Kulachenko, Artem
    et al.
    Solid Mechanics, KTH.
    Lindström, Stefan B
    Mid Sweden University.
    Uesaka, Tetsu
    Mid Sweden University.
    Strength of wet fiber networks: Size scaling2009In: Papermaking Research Symposium, 2009Conference paper (Refereed)
    Abstract [en]

    In this work we investigate the strength scaling of wet fiber networks with the help of particle level network simulations. The objective is to identify the factors that control wet strength distributions and the way it changes with the size. This question is relevant for wet strength runnability. The simulations show that if the mean values of network properties are kept constant by process conditions, the disordered structure of the network produces only small scatters in strength for a sufficiently big network. The strength distribution at small scales does not follow weakest-link scaling with neither change of length nor width, presumably, due to the fact that "damage" clusters are too big compared to the size of considered networks.

  • 16.
    Kulachenko, Artem
    et al.
    Solid Mechanics, KTH.
    Uesaka, T.
    Mid Sweden University.
    Lindström, Stefan B
    Mid Sweden University.
    Reinventing mechanics of fiber networks2008In: Progress in Paper Physics Seminar, 2008, p. 185-187Conference paper (Other academic)
  • 17.
    Lavrykov, Sergiy
    et al.
    State University of New York, Dept of Paper and Bioprocess Engineering.
    Lindström, Stefan B
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Singh, K. M.
    International Paper Co..
    Ramarao, Bandaru
    State University of New York, Dept of Paper and Bioprocess Engineering.
    3D network simulations of paper structurewith fines and fillers2012In: Nordic Pulp and Paper Research Journal, ISSN 0283-2631, Vol. 27, no 2, p. 256-263Article in journal (Refereed)
    Abstract [en]

    The structure of paper influences its properties and simulations of it are necessary to understand the impact of fiber and papermaking conditions on the sheet properties. We show a method to develop a representative structure of paper by merging different simulation techniques for the forming section and the pressing operation. The simulation follows the bending and drape of fibers over one another in the final structure and allows estimation of sheet properties without recourse to arbitrary bending rules or experimental measurements of density and/or RBA. Fibers are first modeled as jointed beams following the fluid mechanics in the forming section. The sheet structure obtained from this is representative of the wet sheet from the couch. The pressing simulation discretizes fibers into a number of solid elements around the lumen. Bonding between fibers is simulated using spring elements. The resulting fiber network was analyzed to determine its elastic modulus and deformation under small strains. The influence of fiber dimensions, namely fiber lengths, widths and thicknesses as well as bond stiffnesses on the elasticity of the network are studied. A brief account of inclusion of fines, represented by individual cubical elements is also shown.

  • 18.
    Lindström, Stefan B
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Modeling and simulation of paper structure development2008Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A numerical tool has been developed for particle-level simulations of fibre suspension flows, particularly forming of the fibre network structure of paper sheets in the paper machine. The model considers inert fibres of various equilibrium shapes, and finite stiffness, interacting with each other through normal, frictional, and lubrication forces, and with the surrounding fluid medium through hydrodynamic forces. Fibre–fluid interactions in the non-creeping flow regime are taken into account, and the two-way coupling between the solids and the fluid phases is included by enforcing momentum conservation between phases. The incompressible three-dimensional Navier–Stokes equations are employed tomodel themotion of the fluid medium.

    The validity of the model has been tested by comparing simulation results with experimental data from the literature. It was demonstrated that the model predicts well the motion of isolated fibres in shear flow over a wide range of fibre flexibilities. It was also shown that the model predicts details of the orientation distribution of multiple, straight, rigid fibres in a sheared suspension. Furthermore, model predictions of the shear viscosity and first normal stress difference were in fair agreement with experimental data found in the literature. Since the model is based solely on first principles physics, quantitative predictions could be made without any parameter fitting.

    Based on these validations, a series of simulations have been performed to investigate the basic mechanisms responsible for the development of the stress tensor components for monodispersed, non-Brownian fibres suspended in a Newtonian fluid in shear flow. The effects of fibre aspect ratio, concentration, and inter-particle friction, as well as the tendency of fibre agglomeration, were examined in the nonconcentrated regimes. For the case of well dispersed suspensions, semi-empirical relationships were found between the aforementioned fibre suspension properties, and the steady state apparent shear viscosity, and the first/second normal stress differences.

    Finally, simulations have been conducted for the development of paper structures in the forming section of the paper machine. The conditions used for the simulations were retrieved from pilot-scale forming trial data in the literature, and from real pulp fibre analyses. Dewatering was simulated by moving two forming fabrics toward each other through a fibre suspension. Effects of the jet-to-wire speed difference on the fibre orientation anisotropy, the mass density distribution, and three-dimensionality of the fibre network, were investigated. Simulation results showed that the model captures well the essential features of the forming effects on these paper structure parameters, and also posed newquestions on the conventional wisdom of the forming mechanics.

  • 19.
    Lindström, Stefan B
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Simulation of the dynamics of fiber suspension flows2007Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    A new model for simulating non-Brownian flexible fibres suspended in a Newtonian fluid has been developed. Special attention has been given to include realistic flow conditions found in the industrial papermaking process in the key features of the model; it is the intention of the author to employ the model in simulations of the forming section of the paper machine in future studies.

    The model considers inert fibres of various shapes and finite stiffness, interacting with each other through normal, frictional and lubrication forces, and with the surrounding fluid medium through hydrodynamic forces. Fibre-fluid interactions in the non-creeping flow regime are taken into account, and the two-way coupling between the solids and the fluid phase is included by enforcing momentum conservation between phases. The incompressible three-dimensional Navier-Stokes equations are employed to model the motion of the fluid medium.

    The validity of the model has been tested by comparing simulation results with experimental data from the literature. It was demonstrated that the model predicts the motion of isolated fibres in shear flow over a wide range of fibre flexibilities. It was also shown that the model predicts details of the orientation distribution of multiple straight, rigid fibres in a sheared suspension. Model predictions of the viscosity and first normal stress difference were in good agreement with experimental data found in the literature. Since the model is based solely on first-principles physics, quantitative predictions could be made without any parameter fitting.

  • 20.
    Lindström, Stefan B
    et al.
    Department of Fiber Technology, KTH.
    Cervin, N. T.
    Department of Fiber Technology, KTH.
    Wågberg, L.
    Department of Fiber Technology, KTH.
    Thermally activated capillary intrusion of water into cellulose fiber-based materials2011In: The proceedings of the Fundamental and Applied Pulp & Paper Modelling Symposium 2011: August 24-28 2011, Concordia University, Montréal, Canada / [ed] Roger Gaudreault; Sylvain Robert; M A Whitehead, PAPTAC , 2011, p. 13-26Chapter in book (Refereed)
    Abstract [en]

    The imbibition of water into cellulose fiber-based materials is studied with focus on the regime dominated by contact line dynamics rather than hydrodynamic drag of the bulk porous structure. Capillary rise is studied under the influence of gravity for different paper grades with a wide range of porosities. It is found that the capillary rise is logarithmic in time in the limit of long time-scales. This behavior is in excellent agreement with the Molecular Kinetics Theory (MKT) for contact line dynamics. For high-porosity paper grades, this previously neglected logarithmic regime starts already at about $5$\,cm of capillary intrusion, underscoring the critical importance of the contact line dynamics to the performance of cellulosic absorbents.

  • 21.
    Lindström, Stefan B
    et al.
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Karabulut, Erdem
    Department of Fiber Technology, KTH.
    Kulachenko, Artem
    Solid Mechanics, KTH.
    Sehaqui, Houssine
    Department of Fiber Technology, KTH.
    Wågberg, Lars
    Department of Fiber Technology, KTH.
    Mechanosorptive creep in nanocellulose materials2012In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 19, no 3, p. 809-819Article in journal (Refereed)
    Abstract [en]

    The creep behavior of nanocellulose films and aerogels are studied in a dynamic moisture environment, which is crucial to their performance in packaging applications. For these materials, the creep rate under cyclic humidity conditions exceeds any constant humidity creep rate within the cycling range, a phenomenon known as mechanosorptive creep. By varying the sample thickness and relative humidity ramp rate, it is shown that mechanosorptive creep is not significantly affected by the through-thickness moisture gradient. It is also shown that cellulose nanofibril aerogels with high porosity display the same accelerated creep as films. Microstructures larger than the fibril diameter thus appear to be of secondary importance to mechanosorptive creep in nanocellulose materials, suggesting that the governing mechanism is found between molecular scales and the length-scales of the fibril diameter.

  • 22.
    Lindström, Stefan B
    et al.
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Karabulut, Erdem
    Department of Fiber Technology, KTH.
    Kulachenko, Artem
    Solid Mechanics, KTH.
    Wågberg, Lars
    Department of Fiber Technology, KTH.
    Discriminating between different mechanosorptive creep hypotheses2011In: / [ed] Ulrich Hirn, Graz, Austria: TU , 2011, p. 121-126Conference paper (Other academic)
  • 23.
    Lindström, Stefan B
    et al.
    Mid Sweden University.
    Kulachenko, Artem
    Espoo, Finland.
    Uesaka, Tetsu
    Quebec, Canada.
    New insights in paper forming using particle-level process simulation2009In: Papermaking Research Symposium, 2009, p. 1-4Conference paper (Other academic)
    Abstract [en]

    A numerical model for simulating forming at particle-level is presented, and the procedure for simulating modern forming equipment is outlined. Simulations were conducted using fiber furnishes composed from different shares of softwood kraft, softwood TMP, and hardwood kraft pulps, and the simulated sheets were analysed for wet strength and stiffness.

  • 24.
    Lindström, Stefan B
    et al.
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Lavrykov, Sergiy
    State University of New York, Dept of Paper and Bioprocess Engineering.
    Singh, K. M.
    International Paper Co..
    Ramarao, Bandaru
    State University of New York, Dept of Paper and Bioprocess Engineering.
    Forming of paper sheets: A numerical simulation based on hydrodynamics of fibrous suspensions2012Conference paper (Other academic)
    Abstract [en]

    A fiber-level simulation of paper forming in a twin-wire roll former is conducted with a furnish typical of fine paper. A mix of bleached kraft softwood and hardwood pulps was chosen, each refined to different levels.  The resultant web structure obtained from the couch roll was determined from these numerical experiments. This wet web structure is used as input to a simulation of wet pressing, which produces a consolidated sheet structure. Results regarding how the change in fiber mix (e.g. HW/SW ratio) and changes in pulp refining affect the structure of the web are shown. Important features such as sheet fiber orientations, anisotropy, retention of fibers, fines and fillers and sheet exit moisture are all predicted by the simulation.

  • 25.
    Lindström, Stefan B
    et al.
    Mid Sweden University, Sundsvall, Sweden.
    Uesaka, T.
    Mid Sweden University, Sundsvall, Sweden.
    Paper structure modeling with particle-level process simulation2006In: Progress in Paper Physics Seminar, 2006Conference paper (Other academic)
    Abstract [en]

    Print quality is highly dependent on the interactions of paper, ink and printing plate at the length scales of half-tone dot size and floc size. Knowledge of the details of the micro-structure is needed to predict these interactions, but it is difficult to obtain experimentally. One way to recreate the micro-structures of paper and to gain understanding of the mechanisms behind their formation is to systematically model each unit process of papermaking at particle level. The output of such simulations is numerical descriptions of the three-dimensional paper structure, from which any structural data can be accessed. Consequently, the simulations relate process parameters and particle properties directly to the micro-structures of paper. Many characteristics of the fiber network structure and the distribution of fillers and fines are determined in the headbox and during drainage in the forming section. A model for fiber suspensions, which couples the Navier-Stokes equations to a mechanical model of discretely represented flexible fibers, has been developed. Its performance allows for the study of large particle systems at very high Reynolds numbers (20000 particles at Re=40000), which is enough to model the conditions prevalent in the forming section of a modern paper machine.

  • 26.
    Lindström, Stefan B
    et al.
    Mid Sweden University.
    Uesaka, T.
    Mid Sweden University.
    Particle-level simulation of forming of the fiber network in papermaking2008In: International Journal of Engineering Science, ISSN 0020-7225, Vol. 46, no 9, p. 858-876Article in journal (Refereed)
    Abstract [en]

    A model for particle-level simulation of fiber suspensions has been used to simulate paper sheet forming on a roll-blade former. The fibers were modeled as chains of fiber segments, flowing and interacting with the medium and with each other. The incompressible three-dimensional Navier-Stokes equations were used to describe the fluid motion. Real pulps were analyzed to provide raw material data for the simulations. Dewatering was simulated by moving two model forming fabrics toward each other through a fiber suspension. Close examination of the dewatering process revealed that no large concentration gradients develop through the thickness of the pulp suspension. In this sense, twin-wire dewatering does not resemble a filtration process. The effects of the jet-to-wire speed difference on the network structure of the paper were investigated. The structural features of interest were fiber orientation anisotropy, mass density distribution and three-dimensionality of the fiber network. It was demonstrated that these simulated structural features were at least in qualitative agreement with experimental data found in the literature.

  • 27.
    Lindström, Stefan B
    et al.
    Mid Sweden University, Sundsvall, Sweden.
    Uesaka, T.
    Mid Sweden University, Sundsvall, Sweden.
    Suspensions of flexible fibers in flows of decaying turbulence2006In: Euromech, 2006Conference paper (Refereed)
  • 28.
    Lindström, Stefan B
    et al.
    Mid Sweden University.
    Uesaka, Tetsu
    A model for flexible fibers in viscous and inert fluid2007In: International Paper Physics Conference, 2007, p. 23-28Conference paper (Refereed)
    Abstract [en]

    A model is proposed for simulating the motion of flexible fibers in fluid flow. Care has been taken to include typical papermaking conditions into the validity range of the model. Fibres are modeled as chains of fiber segments, whose motion is governed by Newton’s second law. The fluid motion is calculated from the three-dimensional incompressible Navier-Stokes equations. By enforcing momentum conservation, the two-way coupling between the solids and fluid phase is taken into account. Fiber–fiber interactions as well as self-interactions include normal, frictional and lubrication forces. Furthermore, the model considers nonlaminar fiber–fluid interactions and particle inertia. Simulation results were compared with experimental data found in the literature. The model predicts very well the orbit period of rigid fiber motion in shear flow. Quantitative predictions were made for the amount of bending of flexible fibers in shear flow. It was also possible to reproduce the different regimes of motion of flexible fibers in shear flow, ranging from rigid motion to coiled motion and self-entanglement.

  • 29.
    Lindström, Stefan B
    et al.
    Mid Sweden University.
    Uesaka, Tetsu
    Mid Sweden University.
    Effects of interparticle friction on the rheology of fiber suspensions2008In: 5th Euro. Congress Comput. Meth. Sci. Eng., 2008Conference paper (Other academic)
    Abstract [en]

    Controlling the rheology of fibre suspensions is of critical importance in papermaking and composites processing; the spatial distribution and orientation distribution of fibres are retained in the final structure of the produced materials, significantly affecting their performance in end-use.

  • 30.
    Lindström, Stefan B
    et al.
    Mid Sweden University.
    Uesaka, Tetsu
    Mid Sweden University.
    Simulation of paper structure development in a roll-blade former2008In: Progress in Paper Physics Seminar, 2008, p. 139-141Conference paper (Other academic)
    Abstract [en]

    Print quality is largely dependent on the variations of paper properties on the length scales of halftone dot size and floc size. By simulating forming of the paper sheet at a particle level, it is possible to extract detailed information about the fibre network at microand mesoscales. Moreover, simulations yield equally detailed information about the development of the fibre network structure, and may thus give new insights in the mechanisms governing its formation.

  • 31.
    Lindström, Stefan B
    et al.
    Mid Sweden University.
    Uesaka, Tetsu
    Mid Sweden University.
    Stochastic modeling of paper structure: Effects of forming section2005In: 5th Biennial Johan Gullichsen Colloquium, 2005, p. 25-35Conference paper (Other academic)
    Abstract [en]

    A new model for particle-level simulation of forming was developed. A set of process parameters and a statistical description of the stock were provided as inputs to the model and a three-dimensional model paper was produced. This allowed the analyses of the relations between process parameters and structural properties of the formed sheet. Numerical experiments were set up to study the effects of the yarns of the forming fabric on the surface distributions of fillers and fines and to investigate the fiber orientation anisotropy and specific formation as functions of the jet-to-wire speed ratio.

  • 32.
    Lindström, Stefan B
    et al.
    Mid Sweden University.
    Uesaka, Tetsu
    Mid Sweden University.
    Hirn, U.
    Graz, Austria.
    Evolution of the paper structure along the length of a twin-wire former2009In: 14th Fund. Res. Symp. / [ed] I’Anson, S. J., The Pulp and Paper Fundamental Research Society , 2009, Vol. 1, p. 207-245Chapter in book (Refereed)
    Abstract [en]

    A particle-level numerical model is used to simulate forming with a twin-wire former configuration. The development of the paper structure along the length of the former is observed to explain the effects of the dewatering elements on the paper structure at different jet-to-wire speed ratios, consistencies, and target basis weights. The simulations indicate that most of the structure development takes place in the initial part of forming (forming roll) and, in some instances, at the drop to atmospheric pressure after the forming roll. Dramatic effects on the through-thickness fibre orientation anisotropy are observed when the consistency is varied by changing the jet thickness, while changes in basis weight had less impact. The through-thickness concentration gradient was almost uniform throughout the forming process, except in the lower range of typical papermaking consistencies. This indicates that the dewatering mechanism is normally thickening, rather than filtration.

  • 33.
    Nygårds, Sofie
    Linköping University, Department of Physics, Chemistry and Biology.
    Nanocellulose in pigment coatings: Aspects of barrier properties and printability in offset2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Papers are coated in order to improve the properties of the surface, to improve printability and to include new functionalities like barriers properties. Typical coating formulation contains a high number of components, some are made from minerals and others are manufactured from petroleum. The barrier properties of today's paper based packages are plastics and/or aluminum             foil. Environmentally friendly substitutie of these nonrenewable materials are needed.  Nanocellulose is a promising material                 and of a growing interest as an alternative to petroleum-based materials, since nanocellulose films/coatings have been shown to have excellent mechanical and barrier properties.

     

    This project aimed to evaluate nanocellulose in combination with minerals in paper coatings. The project had two approaches. One was to evaluate the barrier properties of MFC coatings with mineral included. The second part was about coatings for           printing matters, and evaluation of the possibility to replace petroleum-based binders in the coating color with MFC. Barrier properties were evaluated by measuring the air permeability of the coatings. The properties of the coating affecting the         printability in offset printing examined was the surface energy, the gloss, the roughness of the coatings, the strength and the offset ink setting.

     

    Carboxymethylated nanocellulose formed denser films and had superior barrier properties compared with enzymatically pretreated nanocellulose. Adding of minerals did not affect the barrier properties of the MFC coatings to a significant extent.         Therefore, minerals cannot be added to enhance the barrier but it can be added to reduce the cost of the coating process without losing any barrier properties. 

     

                                 The print quality depends on how the ink interacts with the coating. These coatings did have a relatively high surface energy, which is preferable for printing with waterborne ink. It was also shown that the absorption abilities increased when the amount of MFC was increased. However, offset printing demands high surface strength and addition of MFC in the coating color                     drastically decreased the strength. This means that the coatings produced in this work are not strong enough and thereby not           suitable for offset printing. However other printing technologies put lower demand on surface strength and are still possible.   

     

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