Cross Machine Direction Research Articles

Digital Twin Model of Paper-Aluminum Laminates for Sustainable Packaging.

The proposed integrated experimental and simulation study focuses on the mechanical behavior and failure analysis of coupled paper-aluminum (paper-Al) laminates for sustainable packaging. The research employs an innovative experimental approach combining uniaxial loading with in situ visualization of sample deformation. The acquired experimental data are utilized to validate a simulation model, ensuring its accuracy and reliability. Parametric studies conducted through the finite element model further enhance our understanding of the mechanical behavior of the coupled laminates. Specifically, the study investigates microscopic mechanisms influencing the overall response of laminates in both the machine direction (MD) and the cross-machine direction (CD), presenting a comparative analysis with traditional aluminum-polyethylene (Al-PE) laminates, which is a prevalent choice in the packaging industry. The findings contribute to a better comprehension of key factors affecting the mechanical behavior of paper-Al laminates, enabling the design of more effective and sustainable solutions for the packaging industry. Results indicate the advantage of increasing the laminate thickness in the MD, demonstrating an enhanced strength. Conversely, the sensitivity of the thickness variation in the CD is found to be less pronounced. Additionally, our investigation highlights the substantial potential of paper-based materials as environmentally friendly alternatives, particularly in contrast to Al-PE laminates. Furthermore, integrating an innovative digital twin model, which combines experimental data and simulation, significantly advances our understanding and application of laminated in the context of paper packaging design.

Foam-laid extensible paper for improved extensibility and press-forming performance

This study was motivated by the recent raising interest for the sustainable plastic-free dry 3D formable materials. 3D forming processes are capable to produce large unit quantities, but the process conditions for packaging applications have been typically very demanding for cellulose-based materials. This study covers some of the key factors affecting the extensibility of cellulose fibre-based materials and presents a laboratory-scale development study of a press-formable material concept. The investigation focused on comparisons of two refining concepts for bleached softwood kraft (BSK) pulp and two sheet forming concepts, namely water-laid and foam-laid forming. Additionally, influence of thermoplastic additives on the extensibility and 3D forming performance were investigated. In-plane compaction was applied with Expanda® laboratory device. Performance of the materials was evaluated by tensile tests and depth of the 3D formed shapes. In this study, in-plane compaction at first in cross-machine direction (CD) and then in machine direction (MD) led to over 30% elongation with BSK-based laboratory sheets containing latex as a binder and foaming agent. In addition to high elongation, optimal strength was needed for the best press-forming performances. In-plane compaction was the most significant factor regarding the elongation, but it also decreased the strength of the materials. Similar press-forming performance was found with two materials with either highly anisotropic or more isotropic elongation. The elongation anisotropy was created by one-way and two-way in-plane compactions. The results indicate that a reasonable performance for BSK-based materials for 3D forming applications can be reached using the presented concept.

A novel in-situ micro-mechanical testing of paper fracture and its stochastic network model

Understanding and simulating the evolution of fracture in cellulose-based paper materials is vital for many eco-sustainable applications of packaging solutions. In this work, we conduct an integrated experimental-statistical mechanics analysis to elucidate how the microstructural mechanisms govern the fracture behavior of paper. We employ in-situ tensile tests combined with confocal microscopy to observe and analyze key microstructural phenomena, such as fibers’ activation and recruitment, and progressive tensile failure of unnotched paper samples under uniaxal loading. The developed stochastic mechanics critical cross-section model to treat the cellulose fiber network is able to decouple the stochastic morphological parameters from the constitutive model of the fibers. Notably, it robustly predicts the anisotropic properties of paper materials in the machine direction (MD) and cross-machine direction (CD) as a direct consequence of the different statistical distribution of fibers’ orientation, for the same fiber constitutive model. The proposed approach is finally employed to get an insight into the role of the main morphological parameters, local/non-local fibers’ strain redistribution, and finite elasticity of fibers on the whole mechanical behavior of paper.

Heterogeneity characterization of commercial structural papers

Abstract Evaluation of physical and mechanical heterogeneity in commercial paperboards is needed to promote their use in structural applications, especially within the field of packaging. Understanding the range of their behaviors is needed to compete with other materials in the current marketplace and expand in others. This work describes the physical and stiffness heterogeneities of twelve commercial materials using tensile tests in the cross-machine direction and several inverse analyses. The effects of grammage, thickness, and apparent density on tensile stiffness were evaluated in both the linear elastic and nonlinear regimes. Thickness and density provided the best explanation for elastic heterogeneous behavior in most of the materials; local grammage was not the best descriptor for any material. The analyses used here were not able to provide a good explanation of the nonlinear behavior, which was attributed to the development of large shear strains within the materials as they neared failure. This work provides a methodology for additional heterogeneous behavior examinations.

Control of Meniscus Formation Using an Electrohydrodynamics Module in Roll-to-Roll Systems for the Stable Coating of Functional Layers.

In fabricating functional layers, including thin-film transistors and conductive electrodes, using roll-to-roll (R2R) processing on polymer-based PET film, the instability of the slot-die coating meniscus under a high-speed web impedes functional layer formation with the desired thickness and width. The thickness profiles of the functional layers significantly impact the performance of the final products. In this study, we introduce an electrohydrodynamic (EHD)-based voltage application module to a slot-die coater to ensure the uniformity of the cross-machine direction (CMD) thickness profile within the functional layer and enable a stable, high-speed R2R process. The module can effectively control the spreadability of the meniscus by utilizing variations in the surface tension of the ink. The effectiveness of the EHD module was experimentally verified by applying a high voltage to a slot-die coater while keeping other process variables constant. As the applied voltage increases, the CMD thickness deviation reduces by 64.5%, and the production rate significantly increases (up to 300%), owing to the formation of a stable coated layer. The introduction of the EHD-based application module to the slot-die coater effectively controlled the spreadability of the meniscus, producing large-area functional layers.

Modeling the flexural rigidity of spunlace nonwoven fabrics

Nonwoven fabrics, especially spunlace varieties, find application across diverse fields. This study presents an analytical model that utilizes the energy method, factoring in bending and torsion strain energies. This model is integrated with the dynamic recursive splitting (DYRES) algorithm to predict the flexural rigidity by estimating fiber-to-fiber contacts within spunlace nonwoven fabrics. The input parameters for this proposed model encompass the number of bending couples, the bending stiffness of fibers, and the orientation characteristics of spunlace nonwoven fabrics. To validate the predictive capability of the model, six samples with varying fiber types, basis weights, and thicknesses were fabricated. A comparison between experimental and theoretical values reveals a consistent trend but with overestimated values in both the machine direction (MD) and cross-machine direction (CD). Through the utilization of two coefficients (0.7854 and 0.7823) to refine the presented model, an average relative error of 4.22% and 8.92% was achieved for the MD and CD directions, respectively. This research proposes a theory that utilizes fewer parameters compared to other studies in the field of nonwoven textiles. The proposed approach offers a more convenient and accessible method for obtaining these parameters, as well as determining the bending stiffness of the fabric. Moreover, advanced and more suitable techniques, including knot theory and image processing, have been employed to obtain accurate parameter measurements. This work is believed to lay the foundation for future investigations into the mechanical behavior of nonwoven fabrics.

Filtration behaviour of staple fibre geotextiles under unequal biaxial tensile strains

Gradient ratio tests were conducted to investigate the filtration behaviour of staple fibre needle-punched nonwoven geotextiles subjected to unequal biaxial tensile strains. Three groups of biaxial tensile strains were designed, with the ratios of the strain in the machine direction to that in the cross-machine direction set to 1, 2, and 4, respectively. The strains in the machine direction in the three groups were the same, ranging from 10% to 30%. The tested filtration properties included the gradient ratio (GR), permeability of the soil-geotextile system, mass of soil loss, and permittivity of the pure geotextiles. Comparisons were made between the filtration properties of staple fibre (SN) geotextiles and continuous filament (CN) geotextiles. It is shown that for a certain strain ratio, the GR value at the time of test termination increases with increasing strain, and the permeability of the soil-geotextile system, soil loss, and permittivity of the pure geotextiles decrease with increasing strain. The soil loss and permittivity under equal biaxial tensile strains tend to be higher than those under unequal biaxial tensile strains. The CN geotextiles have better retention capability and more clogging potential for the tested soils than the SN geotextiles for a similar mass per unit area.

Hydrophobic modification of mesh spunlace nonwoven for medical dressing contact layer

The contact layer of traditional medical dressing is easy to adhere to the new wound granulation tissue, which brings the deficiency of secondary wound injury. This work assumed that low-cost and soft mesh spunlace nonwoven was used as medical dressing contact layer. After micro-nano SiO2 modification, polydimethylsiloxane (PDMS)/n-heptane were uniformly sprayed on the surface of materials. PDMS modification was studied by using the three-factor three-level orthogonal experiment. The results showed that when the PDMS concentration was 1%, the heat treatment temperature and time were 120°C and 12 h respectively, material possessed the optimal hydrophobicity and its water contact angle (CA) was 151.0 ± 1.1°. Meanwhile, the hydrophobicity, microstructure, thermogravimetry, composition, tensile mechanics, adhesion resistance and durability of materials with/without treatment were compared. It was proved that PDMS was indeed grafted onto the material and could effectively improve the hydrophobicity in coordination with micro-nano SiO2 without affecting the mesh structure of material. The machine direction (MD) and cross-machine direction (CD) strength of material decreased but the elongation increased slightly. The MD and CD peeling energy was 129.7 ± 33.9 J/m2 and 98.1 ± 38.3 J/m2, respectively. Moreover, the water CA of material modified by micro-nano SiO2/PDMS was still 139.4 ± 1.4° after 10 friction stroke tests, indicating that the modified material possessed the great durability. Overall, this study can provide the research basis for the development of anti-adhesion medical dressing contact layer.

Web Wrinkle Defects due to Temperature Profile in Roll-to-Roll Manufacturing Systems.

The roll-to-roll manufacturing system is extensively used for mass producing products made of plastic, paper, and fabric in several traditional industries. When flexible substrates, also known as webs, are heated and transported inside the dryer, an inconsistent temperature distribution occurs on the material in the machine direction (MD) and cross-machine direction (CMD). If rollers are not aligned in parallel on the same plane in the roll-to-roll web handling process, or if roller misalignment exists, strain deviation occurs in the web, resulting in lateral displacement and web wrinkles. Therefore, this study examined a wrinkle, which is a thermal deformation that occurs when an inconsistent web temperature distribution is formed on the material inside a dryer. The changes in the elastic modulus and thermal expansion of the web were also examined. Experiments were conducted using a PET film, and its elastic modulus and thermal expansion were examined. The results showed that the presence of a web wrinkle defect can cause a thickness deviation in the functional layer manufactured on the web. Moreover, an appropriate operating speed should be set to reduce the CMD temperature deviation, thereby reducing instances of wrinkle defects.

Using machine learning to predict paperboard properties – a case study

Abstract This study aims to investigate the applicability and accuracy of different machine learning (ML) methods for predicting paperboard properties based on raw material and process data. The goal is not to find an ML method that can predict all properties simultaneously, but rather the most suitable method for a single property. The examined properties are bending stiffness and the curl. Furthermore, the focus is not on the most accurate prediction model, but on the best model to interpret. The results show that ML methods are applicable for predicting paperboard properties based on raw material and process data, e. g., bending stiffness and curl in machine direction (MD) and cross-machine direction (CD). The feature selection is crucial for the quality of the prediction. Therefore, domain knowledge is needed to select the right features. This selection improves the model and ensures its reliability, comprehensibility, and interpretability. The self-implemented recursive feature addition (RFA) takes the features specified by a domain expert for the feature selection into consideration. It requires less computation time in comparison to the common recursive feature elimination (RFE). The extremely randomized tree (ET) was chosen due to its high interpretability and good results. It achieves a mean absolute error (MAE) for the bending stiffness MD of 0.913 mN m; an MAE for curl MD of 0.058 m−1 (in a value range from 7 mN m to 100 mN m and −1 m−1 to 1 m−1, respectively); 0.474 mN m and 0.163 m−1 (in a value range from 5 mN m to 45 mN m and −1 m−1 to 2 m−1, respectively) for the respective CD properties.

Experimental Characterization of Anisotropic Mechanical and Thermal Properties of Gas Diffusion Layers

Gas diffusion layer (GDL) is a vital component in proton exchange membrane fuel cells (PEMFC) due its main functions to conduct electrons and heat between the adjacent fuel cell components, provide preferential pathways for product water removal and to provide uniform reactant gas flow distribution to the electrode surface. Because of the anisotropic GDL microstructure, the transport properties vary in the through-plane and in-plane direction. Furthermore, during fuel cell stack assembly pressures exerted on the flowfield land compress the GDL under land cause changes of the GDL microstructure. While moderate compression increases GDL thermal conductivity due to increased fiber-fiber contacts, excessive compression may impede diffusive and liquid water transport due to loss of GDL pore volume. Detailed knowledge of how thermal conductivity is affected by the anisotropic nature of gas diffusion layers under compression is imperative in order to provide a better understanding on how thermal gradients influence two-phase transport during PEMFC operation. Previous research efforts have focused on steady-state methods for measuring effective through-plane GDL thermal conductivity [1][2][3][4] and effective in-plane GDL thermal conductivity [5][6] but to the best of our knowledge no studies have been conducted to measure effective in-plane GDL thermal conductivity for a variety of different GDL types under compression.This study attempts to fill that gap by using specially designed in-house tools to characterize the influence of GDL anisotropy on effective thermal conductivity as a function compression for different GDL types. Furthermore, a comprehensive ex-situ mechanical study is conducted to characterize the compliance matrix for different GDL types. Early results indicate a highly non-linear compressive behaviour in the GDL through-plane direction with large variations for the different GDL types. Moreover, the flexural modulus is found to be highly anisotropic where stiffness in the GDL machine direction (MD) is consistently larger compared to stiffness in GDL cross machine direction (CMD). This work will provide a foundation for a numerical study to couple an anisotropic GDL structural model with a non-isothermal two-phase model to investigate the effects of inhomogenous compression on two-phase transport. Keywords: GDL, PEMFC, ex-situ, anisotropy, modulus, microstructure, mechanical, compression, characterization, MD, CMD, through-plane, in-plane, thermal conductivity[1] G. Karimi, X. Li, P. Teertstra, Electrochim. Acta (2010).[2] R. Bock, A.D. Shum, X. Xiao, H. Karoliussen, F. Seland, I. V. Zenyuk, O.S. Burheim, J. Electrochem. Soc. 165 (2018) F514–F525.[3] G. Unsworth, N. Zamel, X. Li, Int. J. Hydrogen Energy (2012).[4] E. Sadeghi, N. Djilali, M. Bahrami, J. Power Sources (2011).[5] E. Sadeghi, N. Djilali, M. Bahrami, J. Power Sources (2011).[6] N. Alhazmi, D.B. Ingham, M.S. Ismail, K.J. Hughes, L. Ma, M. Pourkashanian, Int. J. Hydrogen Energy (2013).

Relationship between the General Properties and Compression Strength of Commercial Linerboard and Corrugating Medium

Paper packaging is an important sector of the packaging industry. There are several advantages of paper packaging over other materials, such as the ease of obtaining raw materials, low price, high strength at low weight, easy conversion process, and environmentally friendly properties. Liner boards and mediums for corrugated board need adequate properties for end usage, and these properties change depending on the raw materials, production, and conversion processes.BRThe properties of 25 current commercial liner boards and mediums in the domestic market were analyzed for better understanding and utilization. The apparent density, air permeability, internal bond strength, tensile strength, and burst strength, were measured, and the ring crush test (RCT) and short-span compression test (SCT) were performed. The basis weights were changed from 115 to 300 g/㎡, and the air permeability was decreased with higher basis weight. The RCT and SCT compression strengths were increased as the tensile strengths at both of machine direction (MD) and cross-machine direction (CD). As the internal bond strength increased, the MD and CD tensile strengths increased, but a trend was not apparent. The burst strength was increased as the tensile strength increased. The tensile strength, burst strength, and compression strength were correlated very closely. The burst strength increased as the tensile strength increased, and the MD tensile strength had greater effect than the CD tensile strength on increasing the burst strength. Compression strength was improved to a greater degree by the MD tensile strength than by the CD tensile strength. The SCT compression strength with a 0.7 ㎜ span was higher than the RCT strength. The RCT and SCT compression strengths were higher in the MD than in the CD.

Strain Optimization of Tensioned Web through Computational Fluid Dynamics in the Roll-to-Roll Drying Process

Unpredictable web temperature distributions in the dryer and strain deviations in the cross-machine (CMD) and machine (MD) directions could hamper the manufacture of smooth functional layers on polymer-based webs through the roll-to-roll (R2R) continuous process system. However, research on this topic is limited. In this study, we developed a structural analysis model using the temperature distribution of the web as a boundary condition to analyze the drying mechanism of the dryer used in an R2R system. Based on the results of this model, we then applied structural modifications to the flow channel and hole density of the aluminum plate of the dryer. The model successfully predicted the temperature and strain distributions of the web inside the dryer in the CMD and MD by forming a tension according to the speed difference of the driven rolls at both ends of the span. Our structural improvements significantly reduced the temperature deviation of the moving web inside the dryer by up to 74% and decreased the strain deviation by up to 46%. The findings can help prevent web unevenness during the drying process of the R2R system, which is essential to minimize the formation of defects on functional layers built over polymer-based webs.

Relating papermaking process parameters to properties of paperboard with special attention to through-thickness design

A biaxial stress state has been proposed to formulate a failure criterion for paperboard during bending. About 100 paperboards have been splitted, such that top, middle, and bottom plies have been free-laid and tested in the machine direction, cross-machine direction as well as in out-of-plane direction (ZD). The purpose was to determine the failure stresses and its dependency of papermaking parameters: density, degree of orientation, and fiber length for each layer. A linear model to predict the geometrical strength of a plies was suggested. Analytically simulations of different paperboard structures behavior during bending were performed. The density of the middle ply affected the location of the failure position in ZD, as well as the maximum bending moment. The impact of orientation and degree of anisotropy was simulated, which can be used to optimize the ZD property gradient by tweaking the properties, and hence optimize paperboard performance.Graphical abstract

Evaluation of the hygroexpansion of Japanese papers by digital image correlation (3D-DIC) and application to the study of the impact of inlay mounting on the strain of an albumen photographic print

• Inlay-mounted albumen photographic prints become cockled during exhibition. • The mass and the in-plane and out-of-plane displacement of different papers were evaluated by DVS and 3D-DIC as the humidity fluctuated. • The Japanese papers tested have lower strain than the Western paper and, for some samples, very similar hygroexpansion in the machine and cross-machine direction. • The differences in hygroexpansion of the materials may explain the formation of cockles. • DIC can assist in the decision-making process when selecting materials and techniques for conservation treatment. During an exhibition of photographs, a temporary excess of humidity caused waviness to form on some inlay-mounted albumen prints, which persisted and required conservation treatment. In order to understand the origin of this phenomenon, dynamic water sorption (DVS) measurement and digital image correlation (DIC) have been applied to assess the weight and the mechanical behavior of the materials when the humidity varies. The 3D-DIC has been performed using common digital cameras and commercial software. The in-plane hygroexpansion and out-of-plane displacements of various paper samples and of a 19 th -century albumen photographic print, subjected to humidity fluctuation, made it possible to explain the origin and the persistence of waviness of the photograph in an inlay mount. This non-contact and multi-scale technique is therefore particularly useful for assessing the mechanical behavior of cultural heritage materials. It permitted the evaluation of the compatibility or incompatibility between materials depending on the climatic conditions, whether from the point of view of in-plane or out-of-plane displacements, and enabled potential risks linked to thermo-hygrometric variations to be foreseen.

Beverage Coaster Paper - A Protective Paper Grade Development

Beverage coaster paper represents a specialty paper grade, which has its origin in the late 1880s. Its primary function is to serve as a barrier between the beverage and the table surface by soaking up the condensing water of the cold beverage and protect the wooden table surface as well as the customer from droplets of the condensing water.
 A beverage coaster grade was developed utilizing thermos mechanical pulp, bleached softwood and bleached hardwood Kraft pulp. Manufactured on a 48-inch (1219 mm) wide small commercial Fourdrinier paper machine with an oven dry basis weight basis weight of 473.6, and thickness of 886 µm.
 The water absorbance achieved a value 784 g/m² for the top side and 693 g/m² for the wire side of the paper. The smoothness value was 2734 ml/min for the top and 2784 ml/min for the wire side
 The burst index was measured at 0.56 kPa*m²/g, a tear index of 14.68 mNm²/g for the machine direction and 10.78 mNm²/g for the cross machine direction.
 The manufactured beverage coaster paper had no visible signs of dirt and a yellowish white color, an opacity a value of 100%, a brightness of 79.14% and a whiteness of 54.76%. The yellowish white colour had an 95.24% value for the L*, -1.62 for the a*, and 7.23 for the b*.

Lay-Up Compound Matrices for Application of Medical Protective Clothing: Manufacturing Techniques and Property Evaluations.

Medical protective clothing is the first line of defense for medical staff, which makes the acquisition of protection and multiple function challenging. When it comes to contagious diseases, the physical properties of protective clothing are deemed the top priority and, subsequently, they have significant meaning for the structural design, production cost evaluation, convenient production, and innovation. In this study, nonwoven technology is employed to produce matrices in which mechanical properties are supported by Tencel fibers and recycled Kevlar fibers. Next, the electrostatic spinning is conducted to generate breathable and waterproof films. The nonwoven fabrics and membranes are combined to have diverse functions, forming lay-up compound matrices for medical protective clothing. Moreover, measurements are conducted to characterize the lay-up compound matrices in terms of the tensile strength, tearing strength, bursting strength, puncture resistance, stiffness, air-permeable property, surface resistance, comfort performance, sub-micron particulate filtration efficiency, and the penetration of synthetic blood. As for the nonwoven fabrics, the mechanical properties are significantly improved after Kevlar fibers are incorporated. The tensile strength is (62.6 ± 2.4) N along the machine direction (MD) and (50.1 ± 3.1) N along the cross machine direction (CD); the tearing strength is (29.5 ± 1.6) N along the MD and (43.0 ± 1.7) N along the CD; the bursting strength is (365.8 ± 5.0) kPa; and the puncture resistance is (22.6 ± 1.0) N. Moreover, the lay-up compound matrices exhibit a stiffness of (14.7 ± 0.2) cm along the MD and (14.6 ± 0.1) cm along the CD, a surface resistance of (2.85 × 109 ± 0.37 × 109) Ω, an air-permeable property of (45.4 ± 2.3) cm3/s/cm2, and sub-micron particulate filtration efficiency of over 98%. In the measurement for penetration of synthetic blood, the K40/PAN/TPU group prevents the synthetic blood from penetration. Hence, the incorporation of recycled Kevlar fibers and lay-up compound technique creates good physical properties, an appropriate comfort attribute, and functions, which suggests that this study provides a greater diversity and new concepts for the production of medical protective clothing.

Straw Paper for Art Applications – A Paper Development Study

Each paper grade, especially art papers have their own unique requirements by the artist using the paper in regard to mechanical integrity, surface topography, optical appearance and printability based on the unique artistic process applied during printing.
 Wheat straw fiber, a left over product from agricultural operations, can be used in many papermaking grades if properly processed prior to papermaking.
 A wheat straw containing art paper for artistic water color, oil, and encaustic (wax) painting applications was development and produced with a 10% and 15% northern bleached softwood content using a 12-inch (304 mm) wide laboratory scale paper machine, operated at a speed of 3.76 ft/min (1.14 m/min) with and without operating a calendar. The basis weight of the paper product was 350 g/m² with a caliper of 1050 μm to 1640 μm,
 The paper products burst load in psi ranged between 2.49 and 4.71. Tensile peak load measured in kilogram-force (kgf) per 15mm wide testing strip ranged from 4.08 to 9.32 for the machine direction and 1.96 to 4.74 for the cross machine direction.
 The roughness range of the wheat straw art paper was 2909 ml to 2963 ml for the top side and 2880 ml to 2954 ml for the bottom side of the paper.
 The ISO brightness and opacity of the yellowish wheat straw art paper was at 22.74% and 100.00%, The ISO color value was for the L*, a*, b* Hunter color scale 69.46%, 02.02, and 15.47 respectively.
 The finished art paper product met the expectations by the artists. The paper was used for several encaustic art studio projects.

Web lateral instability caused by nonuniform paper properties

Lateral or cross-machine direction (CD) web movement in printing or converting can cause problems such as misregistration, wrinkles, breaks, and folder issues. The role of paper properties in this problem was studied by measuring lateral web positions on commercial printing presses and on a pilot-scale roll testing facility (RTF). The findings clearly showed that CD profiles of machine direction (MD) tension were a key factor in web stability. Uneven tension profiles cause the web to move towards the low-tension side. Although extremely nonuniform tension profiles are visible as bagginess, more often, tension profiles must be detected by precision devices such as the RTF. Once detected, the profiles may be analyzed to determine the cause of web offset and weaving problems. Causes of tension profiles can originate from nonuniform paper properties. For example, by means of case studies, we show that an uneven moisture profile entering the dryer section can lead to a nonuniform tension profile and lateral web movement. Time-varying changes in basis weight or stiffness may also lead to oscillations in the web’s lateral position. These problems were corrected by identifying the root cause and making appropriate changes. In addition, we developed a mathematical model of lateral stability that explains the underlying mechanisms and can be used to understand and correct causes of lateral web instability

Experimental study of gas diffusion layers nonlinear orthotropic behavior

One of the most important components of PEMFC is the gas diffusion layer (GDL), owing to its key role in the reactant diffusion, water management, thermal and electron conductivity. Therefore, the GDL must have an optimal stiffness to ensure these transport functions during numerous hydrothermal cycles. The understanding of its behavior is still a remaining issue. Its orthotropic mechanical behavior requires a series of mechanical characterizations in the plane of the fibers and out of plane. In addition, there are different manufacturing processes for GDL in sheet or roll form to optimize its functional properties. A macro porous layer (MPL) or different PTFE contents might be added by different manufacturers to optimize its performance. In this study, we have performed several mechanical tests differentiating between in plane and out of plane properties in order to characterize different GDLs available on the market. All of the experimental work has been done in the machine (MD) and cross machine direction (CD) according to the fiber orientation. The different GDL types were then classified into categories presenting similar mechanical response.