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The present study concentrates on a series of experiments and numerical analyses for understanding the effects of fiber volume fraction ( VF) and draw ratio ( DR) on the effective elastic properties of unidirectional composites made from an epoxy resin matrix with a continuous fiber reinforcement. Lyocell-type regenerated cellulose filaments (Ioncell) spun with DRs of 3, 6, and 9 were used. In accordance with the specimens in situ, the fibers were modeled as slender solid elements, for which the ratio between the diameter and length was taken to be much less than unity and deposited inside the matrix with the random sequential adsorption algorithm. The embedded element method was thereafter used in the numerical framework due to its computational advantages and reasonable predictions for continuous fiber reinforced composites. Experiments and numerical investigations were carried out, the results of which were compared, and positive trends for both fiber VFs and DRs on the effective properties were observed. The presented experimental and numerical results and models herein are believed to advance the state of the art in the mechanical characterization of composites with continuous fiber reinforcement.

Funding Information: The authors would like to acknowledge the material support by Elastopoli Oy, Finland. Both M.R. and R.A. had equal contributions; therefore, their co-authorship order should be equally assessed. A.K. gratefully acknowledges the funding through the Academy of Finland BESIMAL (Decision No. 334197). Publisher Copyright: © 2021 the Author(s), licensee AIMS Press. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0) In recent years, with the recent advancements in the field of additive manufacturing, the use of biobased thermoplastic polymers and their natural fiber-reinforced biocomposite filaments have been rapidly emerging. Compared to their oil-based counterparts, they provide several advantages with their low carbon footprints, ease of reusability and recyclability and abundancy, and comparable price ranges. In consideration of their increasing usage, the present study focused on the development and analysis of biocomposite material blends and filaments by merging state-of-the-art manufacturing and material technologies. A thorough suitability study for fused deposition modeling (FDM), which is used to manufacture samples by depositing the melt layer-by-layer, was carried out. The mechanical, thermal, and microstructural characterization of birch fiber reinforced PLA composite granules, in-house extruded filaments, and printed specimens were investigated. The results demonstrated the printability of biocomposite filaments. However, it was also concluded that the parameters still need to be optimized for generic and flawless filament extrusion and printing processes. Thus, minimal labor and end-products with better strength and resolutions can be achieved.

Using foam as a carrier fluid in papermaking gives interesting new opportunities. Foam as a more viscous fluid than water is expected to behave differently in a dynamic process. This study presents results obtained under dynamic forming conditions in a semi-pilot scale research environment. Effects of process configurations and running conditions on increased forming speed, web properties, and difference between water-laid and foam-laid processes are shown. The studies were carried out using a water-laid former and the same environment modified for foam forming. In order to achieve increased forming speed, the open headbox was replaced with a closed headbox, and the former geometry was updated. The process foam was boosted with an additional foam pulper. The foam pulper was used as a machine chest for improving the dispersion of fibers into the foam. A much broader tensile strength ratio range (~3 to 8) was achieved with foam forming than with water-laid forming. Foam-laid paper had a broader pore size distribution and higher mean pore size. Formation and the formation spectra of foam-laid sheets were more uniform, leading to improvements in the properties of the fiber network.

Funding Information: Funding: The authors gratefully acknowledge the funding from Academy of Finland BESIMAL project (decision number 334197). J.W. also acknowledges the funding from Jenny and Antti Wihuri Foundation. Publisher Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. Innovations in industrial automation, information and communication technology (ICT), renewable energy as well as monitoring and sensing fields have been paving the way for smart devices, which can acquire and convey information to the Internet. Since there is an ever-increasing demand for large yet affordable production volumes for such devices, printed electronics has been attracting attention of both industry and academia. In order to understand the potential and future prospects of the printed electronics, the present paper summarizes the basic principles and conventional approaches while providing the recent progresses in the fabrication and material technologies, applications and environmental impacts.

Innovations in industrial automation, information and communication technology (ICT), renewable energy, monitoring and sensing fields have been paving the way for smart devices, which can acquire and convey information to the internet, in every aspect of our lives. Since there is ever-increasing demand for large yet affordable production volumes for such devices, printed electronics has been attracting great attention in both industrial and academic research. In order to understand the potential and future prospects of the printed electronics, the present paper summarizes the basic principles and conventional approaches while providing the recent progresses in the fabrication and material technologies, applications and environmental impacts.

Fibrous materials such as paper, nonwovens, textiles, nanocellulose based-biomaterials, polymer networks and composites are widely used versatile engineering materials. Deformations at the fiber network scale have direct role in their effective mechanical behavior. However, computational description of the deformations is a challenge due to their stochastic characteristics. In consideration to this issue, the current study presents a computational homogenization framework at the fiber network scale to investigate how the fiber properties affect the mechanical properties at material scale. Methodology is based on (I) geometrical, spatial and mechanical modelling of fibers and fiber-to-fiber interactions, (II) formation of fiber network solution domain, boundary nodes on the solution domain and control nodes of the domain bounding the solution domain. The boundary value problem is then defined at the fiber network scale and solved with the proposed framework using the Euclidean bipartite matching coupling the boundary nodes and the control nodes represented in the form of corner, edge and surface nodes. The computed results show that the framework is good at capturing the fibrous material characteristics at different scales and applicable to the solution domains generated with stochastic modelling or image-reconstruction methods resulting in non-conformal meshes with non-matching boundary node distributions.

Image processing methods combined with scanning techniques - for example, microscopy or microtomography - are now frequently being used for constructing realistic microstructure models that can be used as representative volume elements (RVEs) to better characterize heterogeneous material behavior. As a complement to those efforts, the present study introduces a computational homogenization method that bridges the RVE and material-scale properties in situ. To define the boundary conditions properly, an assignment problem is solved using Euclidean bipartite matching through which the boundary nodes of the RVE are matched with the control nodes of the rectangular prism bounding the RVE. The objective is to minimize the distances between the control and boundary nodes, which, when achieved, enables the bridging of scale-based features of both virtually generated and image-reconstructed domains. Following the minimization process, periodic boundary conditions can be enforced at the control nodes, and the resultingboundary value problem can be solved to determine the local constitutive material behavior. To verify the proposed method, virtually generated domains of closed-cell porous, spherical particle-reinforced, and fiber-reinforced composite materials are analyzed, and the results are compared with analytical Hashin-Shtrikman and Halpin-Tsai methods. The percent errors are within the ranges from 0.04% to 3.3%, from 2.7% to 14.9%, and from 0.5% to 13.2% for porous, particle-reinforced, and fiber-reinforced composite materials, respectively, indicating that the method has promising potential in the fields of image-based material characterization and computational homogenization.

Abstract The use of aqueous foams as a carrier fluid for pulp fibers instead of water has re-emerged in the paper and board industry in recent years. In foam forming, a surfactant is needed to reduce the surface tension of the carrier liquid and to create foam as a process fluid and flowing medium. This presents the following questions: (1) How do the water forming and foam forming processes differ? (2) How do the obtained wet/dry fibre sheets differ after forming and after wet pressing? (3) Which differences in the process behavior and sheet properties are due to the surfactant, and which are due to the presence of air bubbles in the flowing medium? The answers to these questions were sought by using an experimental academic approach and by applying a special dynamic vacuum assisted sheet former. Although foams are much more viscous than water, dewatering times were found to be approximately equal in water and foam forming at higher vacuum levels. The hydrodynamic resistance of sheet was approximately constant during water forming, while in foam forming resistance was initially even smaller than in water forming but it increased with time, being substantially higher at the end of the forming process. In certain cases, surfactant alone was found to have a similar, albeit often lower, effect on the sheet properties of foam. Surfactant improved sheet dryness (both after forming and wet pressing), lowered density, and lowered strength properties also in water forming. Foam, on the other hand, had a crucial effect particularly on certain structural properties such as formation and porosity. The difference between water and foam-laid sheets typically reduced in line with higher wet pressing pressure. This suggests that the role of surface tension and foam bubbles in controlling interfiber contact is overridden by wet pressing pressure. Thus applying foam as a carrier fluid has characteristic effects both on the papermaking process and the end product properties. The main features of foam forming can be explained by the chemical effects caused by the surfactant, and the structural effects caused by the foam bubbles. Graphic abstract

For fibrous materials such as nonwoven fabrics, paper and paperboards, inter-fiber bonds play a critical role by holding fibers, thus providing internal cohesion. Being a physical phenomenon, inter-fiber bonds occur at every fiber crossing and can be also geometrically detected. In relation to the idea, a statistical geometrical model was developed to investigate the effects of fiber geometry, (i.e. length and cross-sectional properties), spatial distribution, (i.e. location and orientation), and specimen size on fiber network connectivity, which refers to inter-fiber bonds at fiber crossings. In order to generate the fiber network, a geometrical fiber deposition technique was coded in Mathematica technical computing software, which is based on the planar projections and intersections of fibers and provided as supplementary material to the present article. According to this technique, fiber geometries in discrete rectangular prismatic segments were generated by using uniform distributions of the geometrical and spatial parameters and projected onto the transverse plane. Then, projected geometries were trimmed within the transverse boundaries of the specified specimen shape, rectangular prism in this particular study. After this step, fiber crossings were determined through a search algorithm, which was also used as the basis for the fiber spatial regeneration. Thereafter, fibers were accumulated on top of each other by taking fiber crossings into account and eventually fiber networks based on selected properties were formed. By means of the proposed technique, a series of simulation experiments were conducted on paper fiber networks to investigate the correlation between the fiber network connectivity and fiber length, cross-sectional properties, orientation and specimen length, width and thickness.

In the original publication of the article, the sentences ‘‘Hirasaki and Lawson (1985) found a decrease by almost a factor of 104 occurring in the apparent viscosity of foam (air content 83%) in capillary tubes as the ratio of bubble radius to tube radius, , increased from 0.1 to 10. When was 10 they reported apparent foam viscosities as much as 60% below that of water.’’ appearing in fifth paragraph under the sub-section ‘‘Forming of water-laid and foam-laid structures’’ were published incorrectly.The correct one is provided below: Hirasaki and Lawson (1985) found a decrease by almost a factor of 104 occurring in the apparent viscosity of foam (air content 83%) in capillary tubes as the ratio of bubble radius to tube radius, rB=R, increased from 0.1 to 10. When rB=R was 10, they reported apparent foam viscosities as much as 60% below that of water.

We systematically investigated the effect of film-forming polyvinyl alcohol and crosslinkers, glyoxal and ammonium zirconium carbonate, on the optical and surface properties of films produced from TEMPO-oxidized cellulose nanofibers (TOCNFs). In this regard, UV-light transmittance, surface roughness and wetting behavior of the films were assessed. Optimization was carried out as a function of film composition following the “random forest” machine learning algorithm for regression analysis. As a result, the design of tailor-made TOCNF-based films can be achieved with reduced experimental expenditure. We envision this approach to be useful in facilitating adoption of TOCNF for the design of emerging flexible electronics, and related platforms.

Suspensions of mineral pigment and cellulose fibrillar derivatives are materials regularly found in the forest products industries, particularly in paper and board production. Many manufacturing processes, including forming and coating employ flow geometries incorporating extensional flow. Traditionally, colloidal mineral pigment suspensions have been considered to show little to no non-linear behaviour in extensional viscosity. Additionally, recently, nanofibrillar materials, such as microfibrillar (MFC) and nanofibrillar cellulose (NFC), collectively termed MNFC, have been confirmed by their failure to follow the Cox-Merz rule to behave more as particulate material rather than showing polymeric rheological properties when dispersed in water. Such suspensions and their mixtures are currently intensively investigated to enable them to generate likely enhanced composite material properties. The processes frequently involve exposure to increasing levels of ionic strength, coming either from the weak solubility of pigments, such as calcium carbonate, or retained salts arising from the feed fibre source processing. By taking the simple case of polyacrylate stabilised calcium carbonate suspension and comparing the extensional viscosity as a function of post extension capillary-induced Hencky strain on a CaBER extensional rheometer over a range of increasing salt concentration, it has been shown that the regime of constriction changes as the classic DLVO double layer is progressively suppressed. This change is seen to lead to a characteristic double (bimodal) measured viscosity response for flocculated systems. With this novel characteristic established, more complex mixed suspensions of calcium carbonate, clay and MNFC have been studied, and the effects of fibrils versus flocculation identified and where possible separated. This technique is suggested to enable a better understanding of the origin of viscoelasticity in these important emerging water-based suspensions.

The rheology-related effects of nozzle clogging in inkjet printing can seriously affect ink ejection rate and result in irregular droplet trajectory, resulting in poor printing results. In this study three different inkjet inks, used for functional printing with a Dimatix materials inkjet printer, are investigated rheologically. In connection with rheological observation a novel method of inkjet trajectory image analysis gives insight into the irregularity of directional deviation due to clogging of nozzles of the printer It is found that the type of solvent used in the ink formulation has an important influence on the rheological behaviour in the printing regime, which directly has an effect on ink-droplet trajectory and contact characteristic with the substrate.

Appropriate regularization algorithm is proposed for choosing the regularization parameter based on nosy immobilization viscosity data. Complex fluids as nanocelluose based high consistency suspensions have very complex rheological behavior. This paper describes Tikhonov regularization procedure for reducing the noise from immobilization rheograms of nanocellulose based furnishes, performed on immobilization cell at MCR 300 rheometer. Noise observed in immobilization rheograms can make evaluation of data very complicated and lead to wrong interpretation of rheological behavior observed. They are related to the change of consistency accompanied with rearrangement of the particles during shear induced dewatering accompanied with wall slip and boundary effects typical for gel like nanocellulose suspensions. Hereby we propose a model with regularization parameters suitable for applying to parallel disk data for flocculated gel like high consistency suspensions while consistency increasing mode upon shearing .

Nanotechnology allows development of new enabling technologies with broad commercial potential. Cellulose has also the potential to be the source for renewable materials, which can be made multifunctional and self-assembling at the same time displace many non-renewable materials including metal and ceramics. The potential application area includes high quality paper products, paper coatings, high-performance and sustainable composites.Research has focused on small scale testing odnanocellulosesuspensions and matrix of furnish materials in order to study new composite materials. Basic rheological and dewatering properties of nanocellulose based high consistency furnishes were evaluated. Two different grades of nanocellulose, microfibrillated cellulose (MFC) and nanofibrillated cellulose (NFC) with different swelling properties were used. Both types of nanocellulose have a common challenge, namely strong interactions between the particles resulting in aggregation of individual particles. These inter-particle interactions together with the physical entanglements cause high viscosities of nanocellulose suspensions and furnishes, which together with high water bonding property affects processability

An algorithm on geometrical data extraction, material reconstruction and numerical analysis is presented in order to reconstruct the actual wood-like cellular materials and investigate their linear elastic material behavior in the transverse plane under different loading conditions. The algorithm implemented by Mathematica technical computing software is used to read the pixel data of cellular material images with a wide range of material scales, e.g. from micro- to millimeter scale. As a result of this process, geometrical properties including cell wall thicknesses, cell connectivities, vertex and center coordinates are determined. Identified geometrical properties are transferred to Abaqus/CAE computer aided engineering software by using a Python script and also converted into stereolithography STL model format enabling prototype generation and visualization. As an application example, the reconstructed model by means of the algorithm was used to investigate the in-plane effective stiffness properties of Norway spruce earlywood specimens in the frameworks of homogenization and finite element analysis.

The micro-fi brillated cellulose (MFC) is a potential material which will at least partly substitute the synthetic co- binders, such as carboxymethyl cellulose (CMC), in paper coating color formulations. Co-binders play an important role in controlling both the fl ow properties and the dewatering rate of coating colors during the application process as well as during the subsequent fi lm immobilization [25, 19, 02]. In this study, MFC fi bers are used to substitute standard, synthetic co-binder material, CMC, affecting both dewatering and rheological properties of coating colors. This study was partly attempting to establish standard measurement procedures that can give overall picture of complex rheological behavior of MFC coating colors. Elastic effects of coating color in low shear rate infl uence both the fl ow and blade load [23]. By infl uencing leveling, elasticity, substitution of CMC with MFC infl uences coating color application and immobilization process, as well as the uniformity and optical properties of the coating fi lm [06] . It has been demonstrated that coating colors which contained MFC fi bers as a co-binder had pronounced shear-thinning characteristics which is a desirable property for paper coatings. However, a complete substitution of CMC with MFC fi bers in paper coatings induced low retention properties, longer shearrecovery time and fast immobilization of coating colors, which can have a negative infl uence on leveling and fi nal coating layer uniformity.Coating suspension rheology of the coating infl uences the coating performance at high speeds. The quality of the coated and printed papers is also affected by the rheology of the suspension [06,26]. Co-binders play an important role in controlling both the fl ow properties and the dewatering rate of coating colors during the application process as well as during the subsequent fi lm immobilization [23,06]. The micro fi brillated cellulose (MFC) is a potential material which will at least

Biocomposites were prepared by solvent casting from poly(vinyl) alcohol and mechanically microfibrillated (MFC) birch pulp. Preparations varied in concentration of polymer solution, mixing time of cellulose/PVA dispersion and were either degassed or not. In addition, specimens were tested in different levels of relative humidity at a constant temperature. The results show that the preparation method has a significant influence on mechanical properties. It was observed that aggregation of microfibrills was easier at lower concentrations of polymer solution leading to inferior properties of composites. Degassing provided increase in Young’s modulus and tensile strength at MFC loads below 10% (w/w). However, there was no significant change in composites density. Longer mixing time significantly deteriorated mechanical properties of biocomposites. The relative humidity proved to be very important factor. The properties of composites conditioned at 45% RH showed higher strength and stiffness properties than conditioned at 55 %RH. The experimental data were in a good agreement with percolation model.

Thermal conductivity of paper coatings is increasingly important in the performance of many printing processes, including traditional heatset web offset and thermal papers, as well as digital processes, such as electrophotography. This work studies the extension of a Modified Lumped Parameter Model, previously used successfully to describe talc coatings, to model the thermal conductivity–coating structure relationships of calcium carbonate (gcc: 60 wt% < 2 μm) coatings. A series of compact tablets were used to provide experimental values of thermal diffusivity and conductivity. The samples studied covered a range of latex binder addition levels, namely 0–25 parts, based on 100 parts pigment, of 0.2 μm styrene acrylate latex. Combining the observed thermal properties with knowledge of the pore structure changes induced by the latex addition, it is possible to establish initial correlation with the model, in which the connectivity of the structure is increased at low latex dose illustrating the initial increase in effective thermal conductivity. The practically hard sphere properties of the latex used, combined with the broad size distribution of the gcc, produce a disruptive packing effect as the dose level increases, such that the conductivity reflects a competition between the increasing connectivity provided by the latex versus the increasing relative pore size in the network structure. It is recognized that the fixed pigment volume in the model unit cell diverts from a true representation of the residual porosity. At the highest latex dose levels, the intrinsically less conducting properties of the latex begin to dominate.

Polymeric and activated carbon composite membranes were prepared and their morphology quantitatively, tensile properties and performance (flux and cut-off) were characterized. Both types of membranes were prepared by using polysulfone and di-methyl formamide as polymer and solvent, respectively. In order to obtain a wide range of morphologies, two non-solvents were used (water and iso-propanol) and eight coagulation baths were produced by using the non-solvents alone, by mixing them and by mixing each one with the solvent. Numerical values for the main morphological properties of the membrane were determined from micrographs obtained by scanning electron microscopy, atomic force microscopy and IFME® software. The tensile properties were also determined. Finally, the performance of the membranes in terms of flux and cut-off was determined. Results show that varying the coagulation bath can lead to a wide range of morphologies and cut-off. In the range studied, the presence of activated carbon on the membranes does not significantly change the properties studied. Neither the morphology nor the tensile properties are significantly modified. Finally, the presence of water in the coagulation bath very clearly determines the tensile properties of membranes.

Darkening of the fines and fiber fraction of peroxide-bleached thermo-mechanical pulp (TMP) was studied on a laboratory scale using a device that simulates the short circulation of a paper machine. Selected chemicals were dissolved in the circulation water to study the effect of different cations and anions. Ferrous ions darkened the fines and fiber fraction by increasing the light absorption. It is very important to keep the iron content of the pulp and white water as low as possible because even low contents of iron have a negative effect on the brightness of produced paper. Also, chloride ions decreased the brightness by increasing the light absorption of the fines and fiber fraction. Calcium ions increased both the light absorption and light scattering of the fines fraction. The increased light absorption dominated and the brightness decreased. Calcium chloride is used very commonly as a model chemical for calcium ions in laboratory tests, but the use of it is not recommended, if the darkening phenomena are studied, because chloride ions decrease the brightness. Aluminum ions increased the brightness of the fines fraction by increasing the light scattering. Manganese, sodium, sulfate, or carbonate ions did not affect the optical properties.

The slow process in which the light absorbing dye molecules are adsorbed from solution on the nano-crystalline TiO2 photoelectrode film has been a handicap to the fast and cost-effective fabrication of dye-sensitized solar cells (DSSCs) using printing techniques. Here, we report a versatile dye sensitization process, achieved by inkjet printing a concentrated dye solution over the TiO2 film, which produces solar cells with equal performance and stability as obtained using the popular dye drop casting method. In addition to allowing precise control of dye loading required for dispensing just the right amount of dye to achieve uniform and full coloration of the TiO2 films without any need for washing off the excess dye, inkjet printing also makes it possible to freely adjust the amount and position of the dye to create DSSCs with tailored transparency, color density gradients, and patterns of one or more dyes on the same electrode. The method was confirmed to be applicable also for non-transparent, high-efficiency DSSC designs that employ a light scattering layer. The inkjet-dyed DSSCs exhibited high stability, retaining almost 100% of their conversion efficiency (eta = 6.4 +/- 0.2%) and short circuit current density (J(SC) = 14.2 +/- 0.6 mA cm(-2)) when subjected to a 1000 h accelerated aging test under 1 Sun illumination at 35 degrees C, followed by additional 1154 hours under 0.5 Sun at 60 degrees C. These results overcome one of the main hurdles in realizing fully printed DSSCs and open opportunities for entirely new DSSC designs.