| 1. |
- Alzweighi, Mossab, et al.
(författare)
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Predicting moisture penetration dynamics in paper with machine learning approach
- 2024
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Ingår i: International Journal of Solids and Structures. - : Elsevier BV. - 0020-7683 .- 1879-2146. ; 288, s. 112602-
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we predicted the gradient of the deformational moisture dynamics in a sized commercial paper by observing the curl deformation in response to the one-sided water application. The deformational moisture is a part of the applied liquid which ends up in the fibers causing swelling and subsequent mechanical response of the entire fiber network structure. The adapted approach combines traditional experimental procedures, advanced machine learning techniques and continuum modeling to provide insights into the complex phenomenon relevant to ink-jet digital printing in which the sized and coated paper is often used, meaning that not all the applied moisture will reach the fibers. Key material properties including elasticity, plastic parameters, viscoelasticity, creep, moisture dependent behavior, along with hygroexpansion coefficients are identified through extensive testing, providing vital data for subsequent simulation using a continuum model. Two machine learning models, a Feedforward Neural Network (FNN) and a Recurrent Neural Network (RNN), are probed in this study. Both models are trained using exclusively numerically generated moisture profile histories, showcasing the value of such data in contexts where experimental data acquisition is challenging. These two models are subsequently utilized to predict moisture profile history based on curl experimental measurements, with the RNN demonstrating superior accuracy due to its ability to account for temporal dependencies. The predicted moisture profiles are used as inputs for the continuum model to simulate the associated curl response comparing it to the experiment representing “never seen” data. The result of comparison shows highly predictive capability of the RNN. This study melds traditional experimental methods and innovative machine learning techniques, providing a robust technique for predicting moisture gradient dynamics that can be used for both optimizing the ink solution and paper structure to achieve desirable printing quality with lowest curl propensities during printing.
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| 2. |
- Alzweighi, Mossab, et al.
(författare)
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The influence of structural variations on the constitutive response and strain variations in thin fibrous materials
- 2021
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 203
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Tidskriftsartikel (refereegranskat)abstract
- The stochastic variations in the structural properties of thin fiber networks govern to a great extent their mechanical performance. To assess the influence of local structural variability on the local strain and mechanical response of the network, we propose a multiscale approach combining modeling, numerical simulation and experimental measurements. Based on micro-mechanical fiber network simulations, a continuum model describing the response at the mesoscale level is first developed. Experimentally measured spatial fields of thickness, density, fiber orientation and anisotropy are thereafter used as input to a macroscale finite-element model. The latter is used to simulate the impact of spatial variability of each of the studied structural properties. In addition, this work brings novelty by including the influence of the drying condition during the production process on the fiber properties. The proposed approach is experimentally validated by comparison to measured strain fields and uniaxial responses. The results suggest that the spatial variability in density presents the highest impact on the local strain field followed by thickness and fiber orientation. Meanwhile, for the mechanical response, the fiber orientation angle with respect to the drying restraints is the key influencer and its contribution to the anisotropy of the mechanical properties is greater than the contribution of the fiber anisotropy developed during the fiber sheet-making.
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| 3. |
- Brandberg, August, 1990-, et al.
(författare)
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Characterization and impact of fiber size variability on the mechanical properties of fiber networks with an application to paper materials
- 2021
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Cellulose fibers exhibit a wide range of shapes and sizes. This variation influences the mechanical performance of paper and paperboard by affecting the stress distribution inside the network and the degree of fiber-to-fiber bonding which is possible at a given density. However, the methods used to characterize the distribution of fiber sizes in the pulp neglect that the characteristic features of a fiber are generally not independent. Here, we resolve this shortcoming by fitting the fiber population to a multivariate distribution without enforcing normality or independence between the properties. The high-dimensional multivariate function is recast as a set of univariate distribution functions and a series of bivariate distributions connected by a canonical vine. Using a micro-mechanical model of a paper sheet the influence of this improved characterization is investigated. Reasonable margins and a description of the dependency is shown to be superior to assuming independence even for perfectly preserved marginal distributions. This result demonstrates that micro-mechanical models of paper and paperboard cannot by assumption neglect the influence of the interdependence between the characteristic features of fibers.
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| 4. |
- Brandberg, August, 1990-, et al.
(författare)
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The Role of the Fiber and the Bond in the Hygroexpansion and Curl of Thin Freely Dried Paper Sheets
- 2019
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A computationally efficient method to study the in-plane and out-of-plane dimensional instability of thin paper sheets under the influence of moisture changes is presented. The method explicitly resolves the bonded and the free segments of fibers in the network, capturing the effect of anisotropic hygroexpansion at the fiber level. The method is verified against a volumetric model. The importance of longitudinal fiber hygroexpansion is demonstrated in spite of the absolute value of longitudinal hygroexpansion being an order of magnitude lower than the transverse hygroexpansion component. Finally, the method is used to demonstrate the formation of macroscopic sheet curl due to a moisture gradient in structurally uniform sheets in the absence of viscoelastic or plastic constitutive behavior and through-thickness residual stress profiles.
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| 5. |
- Czibula, Caterina, et al.
(författare)
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The transverse and longitudinal elastic constants of pulp fibers in paper sheets
- 2021
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Cellulose fibers are a major industrial input, but due to their irregular shape and anisotropic material response, accurate material characterization is difficult. Single fiber tensile testing is the most popular way to estimate the material properties of individual fibers. However, such tests only determine the longitudinal modulus of the fiber. Here, we compare sheet testing, micromechanical testing, and nanoindentation as methods to extract the elastic material properties of the individual fibers. We show that nanoindentation can be used to determine both the longitudinal and the transverse elastic modulus using only two indentations, additionally enabling the measurement of fiber properties in-situ inside a sheet of paper where the complete process history is captured. For the longitudinal modulus, the accuracy is comparable for larger indents, but with an increase of scatter of unknown origin as the probe size is decreased using an atomic force microscopy tip.
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| 6. |
- Czibula, Caterina, et al.
(författare)
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The transverse and longitudinal elastic constants of pulp fibers in paper sheets
- 2021
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Cellulose fibers are a major industrial input, but due to their irregular shape and anisotropic material response, accurate material characterization is difficult. Single fiber tensile testing is the most popular way to estimate the material properties of individual fibers. However, such tests can only be performed along the axis of the fiber and are associated with problems of enforcing restraints. Alternative indirect approaches, such as micro-mechanical modeling, can help but yield results that are not fully decoupled from the model assumptions. Here, we compare these methods with nanoindentation as a method to extract elastic material constants of the individual fibers. We show that both the longitudinal and the transverse elastic modulus can be determined, additionally enabling the measurement of fiber properties in-situ inside a sheet of paper such that the entire industrial process history is captured. The obtained longitudinal modulus is comparable to traditional methods for larger indents but with a strongly increased scatter as the size of the indentation is decreased further.
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| 7. |
- Godinho, Pedro Miguel J.S., et al.
(författare)
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A continuum micromechanics approach to the elasticity and strength of planar fiber networks : Theory and application to paper sheets
- 2019
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Ingår i: European journal of mechanics. A, Solids. - : Elsevier. - 0997-7538 .- 1873-7285. ; 75, s. 516-531
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Tidskriftsartikel (refereegranskat)abstract
- 2D materials such as planar fibrous networks exhibit several mechanical peculiarities, which we here decipher through a 3D-to-2D transition in the framework of continuum micromechanics or random mean-field homogenization theory. Network-to-fiber concentration (or “downscaling”) tensors are derived from Eshelby-Laws matrix-inclusion problems, specified for infinitely long, infinitely flat fibers, and for infinitely flat spheroidal pores of vanishing stiffness. Overall material failure is associated with microscopic shear failure orthogonal to the fiber direction. Corresponding structure-property relations between porosity on the one hand, and in-plane stiffness as well as strength on the other hand, appear as linear. This is in good agreement with mechanical experiments carried out on pulp fibers, on pulp fiber-to-pulp fiber bonds, and on corresponding paper sheets.
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| 8. |
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| 9. |
- Hirn, Ulrich, et al.
(författare)
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The Area of Molecular Contact in Fiber-Fiber Bonds
- 2013
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Ingår i: Advances in Pulp and Paper Reserach, Cambridge 2013. - 9780992616304 ; , s. 201-223
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Konferensbidrag (refereegranskat)abstract
- We are presenting a coherent theoretical concept as well as empirical evidence suggesting that there is a high degree of molecular contact in fiberfiber bonds, the surfaces might even be in full contact.Fundamental theoretical relations from contact mechanics governing the area in molecular contact between surfaces are reviewed and proposed for the quantitative analysis of the area in molecular contact in fiber-fiber bonds.The key parameters determining the degree of molecular contact according to the theory are indentation hardness and elastic modulus of the wet pulp fibers, surface roughness of the wet fibers and the pressure applied to the fiber bonds during bond formation.We provide results for fiber indentation hardness and effective elastic modulus from nanoindentation measurements of fiber surfaces at varying relative humidity and in water. The fiber surface properties have been determined with an atomic force microscopy technique specifically designed to measure soft, viscoelastic materials. Also, surface roughness has been measured in the wet and dry state.Experiments with individual fiber-fiber joints show that the breaking strength of these joints is independent from the pressure during bond formation indicating that the surfaces in fiber-fiber bonds are in a high degree of molecular contact, maybe even full contact. This is the case even if they are formed without external pressure. Computer simulations of the degree of mechanical contact of fiber surfaces during drying were performed indicating that capillary adhesion is pulling the fiber surfaces into a high degree of molecular contact. These findings are discussed with respect to the literature considering FRET microscopy and Transmission Electron Microscopy of fiber-fiber bonds.
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| 10. |
- Kouko, Jarmo, et al.
(författare)
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Understanding extensibility of paper : Role of fiber elongation and fiber bonding
- 2020
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Ingår i: TAPPI Journal. - : TAPPI Press. - 0734-1415. ; 19:3, s. 125-135
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Tidskriftsartikel (refereegranskat)abstract
- The tensile tests of individual bleached softwood kraft pulp fibers and sheets, as well as the micromechanical simulation of the fiber network, suggest that only a part of the elongation potential of individual fibers is utilized in the elongation of the sheet. The stress-strain curves of two actual individual pulp fibers and one mimicked classic stress-strain behavior of fiber were applied to a micromechanical simulation of random fiber networks. Both the experimental results and the micromechanical simulations indicated that fiber bonding has an important role not only in determining the strength but also the elongation of fiber networks. Additionally, the results indicate that the shape of the stress-strain curve of individual pulp fibers may have a significant influence on the shape of the stress-strain curve of a paper sheet. A large increase in elongation and strength of paper can be reached only by strengthening fiber-fiber bonding, as demonstrated by the experimental handsheets containing starch and cellulose microfibrils and by the micromechanical simulations. The key conclusion related to this investigation was that simulated uniform inter-fiber bond strength does not influence the shape of the stress-strain curve of the fiber network until the bonds fail, whereas the number of bonds has an influence on the activation of the fiber network and on the shape of the whole stress-strain curve.
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| 11. |
- Kouko, Jarmo, et al.
(författare)
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Understanding extensibility of paper : Role of fiber elongation and fiber bonding
- 2019
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Ingår i: Paper Conference and Trade Show, PaperCon 2019. - : TAPPI Press. ; , s. 1354-1365
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Konferensbidrag (refereegranskat)abstract
- The tensile tests of individual bleached softwood kraft pulp fibers and sheets, and micromechanical simulation of fiber network suggest that only a part of the elongation potential of individual fibers is utilized in the elongation of sheet. The stress-strain curves of two actual individual pulp fibers and one classic fiber were applied to a micromechanical simulation of random fiber networks. Both the experimental results and the micromechanical simulations indicated that fiber bonding has an important role not only in determining the strength but also the elongation of fiber networks. Additionally, the results indicate that the shape of the stress-strain curve of individual pulp fibers may have significant influence on the shape of the stress-strain curve of a paper sheet. A large increase in elongation and strength of paper can be reached only by strengthening fiber-fiber bonding, as demonstrated by the experimental handsheets with starch and cellulose microfibrils and by the micromechanical simulations. The key conclusion related to this investigation was that simulated uniform inter-fiber bond strength does not influence the shape of the stress-strain curve of the fiber network until the bonds fail, whereas the number of bonds has an influence on activation of the fiber network and on the shape of stress-strain curve.
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| 12. |
- Lindström, Stefan B, 1974-, et al.
(författare)
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Evolution of the paper structure along the length of a twin-wire former
- 2009
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Ingår i: ADVANCES IN PULP AND PAPER RESEARCH, OXFORD 2009, VOLS 1-3. - Bury, UK : Pulp Paper Fund. Res. Soc.. - 9780954527266 ; , s. 207-245, s. 207-245
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Konferensbidrag (refereegranskat)abstract
- 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 ofthe 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 onthe 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.
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| 13. |
- Magnusson, Mikael S., 1984-, et al.
(författare)
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Interfibre joint strength under peeling, shearing and tearing types of loading
- 2013
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Ingår i: Advances in Pulp and Paper Research, Cambridge 2013. - 9780992616304 ; , s. 103-124
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Konferensbidrag (refereegranskat)abstract
- The mechanical properties of interfibre joints are essential for the load carrying capacity of fibre network materials such as paper and board. Mechanical measurements of fibre–fibre crosses can been used to characterize the strength of these interfibre joints in order to obtain knowledge on how these hierarchical network materials behave at the micrometer scale. The general method for these interfibre joint strength experiments has been to pull one of the fibres of a fibre–fibre cross and attribute the force at rupture to the shear strength of the interfibre joint. However, without taking the geometry of the fibres and the resulting mixed mode of loading at the interfibre joints into account, limited information on the strength properties can be obtained using this technique. In this study, isolated fibre–fibre crosses have been tested mechanically using four distinctly different load cases; peeling, shearing, tearing and a biaxial type of loading, in order to gain more information on how interfibre joints behave in different modes of loading. The centerline geometry of the fibres, microfibril angles, initial twists as well as the wall thickness of each individual test piece was used to model each experiment using the finite element method, and from the simulation results, the local state of loading in the interfibre joints at failure was obtained for each specific experiment. The force–displacement curve for the experiments as well as the estimated local state of loading was also used to compare the different load cases and to evaluate the information that can be obtained on the strength properties of interfibre joints using these load cases.
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| 14. |
- Schaubeder, Jana B., et al.
(författare)
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Role of intrinsic and extrinsic xylan in softwood kraft pulp fiber networks
- 2024
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Ingår i: Carbohydrate Polymers. - 0144-8617. ; 323
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Tidskriftsartikel (refereegranskat)abstract
- Xylan is primarily found in the secondary cell wall of plants providing strength and integrity. To take advantage of the reinforcing effect of xylan in papermaking, it is crucial to understand its role in pulp fibers, as it undergoes substantial changes during pulping. However, the contributions of xylan that is added afterwards (extrinsic) and xylan present after pulping (intrinsic) remain largely unexplored. Here, we partially degraded xylan from refined bleached softwood kraft pulp (BSKP) and adsorbed xylan onto BSKP. Enzymatic degradation of 1 % xylan resulted in an open hand sheet structure, while adsorption of 3 % xylan created a denser fiber network. The mechanical properties improved with adsorbed xylan, but decreased more significantly after enzymatic treatment. We propose that the enhancement in mechanical properties by adsorbed extrinsic xylan is due to increased fiber-fiber bonds and sheet density, while the deterioration in mechanical properties of the enzyme treated pulp is caused by the opposite effect. These findings suggest that xylan is decisive for fiber network strength. However, intrinsic xylan is more critical, and the same properties cannot be achieved by readsorbing xylan onto the fibers. Therefore, pulping parameters should be selected to preserve intrinsic xylan within the fibers to maintain paper strength.
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