Characterisation of 3D porous macrostructure of hollow fibre membranes using X-ray tomography-effects of some spinning process conditions

The presence of pores larger than a micron, known as macrovoids, in polymeric membranes is particular lydetrimental for membrane structural integrity and mechanical properties. The theoretical modelling and physical understanding of the mechanisms of initiation and growth of the macrovoids, notably in order to determine processing conditions that would allow to make macrovoids free membranes, have been the subject of a vast literature and a restill controversial. However, experimental data on macrovoids, that could help to discriminate between several ideas are scarce and have been essentially obtained using 2D imaging systems. A very large number of observations are then needed to obtain statistically significant results and the limitation to 2D images does not permitto access to an accurate description of the macroporous structure. In this work, anX-raytomography system was used to image the 3D porous structure of hollow fibre membranes with a spatial resolution of one micron. Image analysis tools have been developed to accurately characterise them acrovoid shapes and spatial distribution on the membrane outer and inner skins as a function of some of the spinning process conditions (concentration of solvent into the bore and airgap length). The main purpose is there fore to quantify effects of some processing conditions on the macroporous structure of a hollow fibre membrane. Also, such an accurate characterisation of the macrovoids spatial distribution and 3D shape, as well as their variations with the process experimental conditions, help to shed light on macrovoids initiation and growth mechanisms

A comparative study of the effects of pulp fractionation, refining, and microfibrillated cellulose addition on tissue paper properties

International audienceEnvironmental and economic concerns are driving tissue paper manufacturers to improve understanding of the relationships between fibres, the networks they form, the forming process, and the final tissue paper properties. This work investigated how pulp fractionation, refining, or addition of microfibrillated cellulose (MFC) affect the compromise between absorbency and strength of 33 ± 2 g/m² model papers made of bleached eucalyptus kraft pulp. The results showed that the compromise of properties was better when fibres were refined than when MFC was added. The absorbency capacity of 2%wt MFC-paper was almost 20% lower than the capacity of the refined paper at the same dry strength. The calculated additional storage capacity due to water-induced deformations of the fibre network was 40% lower in the same range of bulk. By forming a high viscosity gel at inter-fibre contacts, MFC could limit the occurrence of major fibre and network deformation mechanisms when water was imbibing the paper

REINFORCING FOLDING BOARD BOXES BY PRINTING A PLA PATTERNED GRID ON THEIR PANELS: A NEW APPROCAH FOR LIGHTWEIGHTING STIFF PACKAGING

International audienceThe potential of printing stiffeners of polylactic acid (PLA) by Fused Deposition Modeling (FDM) on the panels of folding board boxes was investigated in view of reducing the board weight while maintaining the box resistance to vertical compression. Cyclic loading and unloading compression tests were performed under standard (50% RH) and humid (85% RH) environmental conditions on boxes printed with different grid patterns. By only adding 7% in weight of PLA to the whole packaging, the performance was improved by 29% under standard conditions and 60% under humid conditions when the inner surface of box panels was printed with an orthogonal-type grid. A comparison with a higher basis weight folding board suggested that 30% of raw materials could be saved. Results suggested that the grid mainly improved the elastic properties of the panels and could delay the buckling of panels and thus the box collapse. Furthermore, the grid pattern could affect the buckling shape that the panels took

Reinforcing folding board boxes by printing a PLA patterned grid on their panels: A new approach for lightweighting stiff packaging

The potential of printing stiffeners of polylactic acid (PLA) by fused deposition modelling (FDM) on the panels of folding board boxes was investigated in view of reducing the board weight while maintaining the box resistance to vertical compression. Cyclic loading and unloading compression tests were performed under standard (50% relative humidity [RH]) and humid (85% RH) environmental conditions on boxes printed with different grid patterns. By only adding 7% in weight of PLA to the whole packaging, the performance was improved by 29% under standard conditions and 60% under humid conditions when the inner surface of box panels was printed with an orthogonal-type grid. A comparison with a higher basis weight folding board suggested that 30% of raw materials could be saved. Results suggested that the grid mainly improved the stiffness of panels and could delay their buckling and thus the box collapse

Etude de l'hygroexpansion du carton plat par une méthode de corrélation d'images obtenues par MEB environnemental et microtomographie aux rayons X = Analysis of paperboard hygroexpansion by digital correlation of images obtained by ESEM and X-ray microtomography

National audienceLe carton plat est un matériau stratifié. Ses couches ont une structure anisotrope et sont formées par des fibres de bois issues de pâtes à papier de différents types. Au cours de sa transformation et de son utilisation, le carton plat est soumis à des variations d'humidité relative de l'air ambiant. Celles-ci peuvent occasionner des problèmes de stabilité dimensionnelle telles que des pertes de planéité du carton et une décohésion de ses couches. Ce phénomène est anisotrope. Assez bien décrit dans le plan, mais assez peu selon l'épaisseur du carton, il est ici étudié au moyen d'outils classiques donnant accès à des coefficients d'hygroexpansion macroscopiques selon les directions d'anisotropie du carton. Une analyse, plus fine, par méthode de corrélation d'images, obtenues par MEB environnemental ou microtomographie aux rayons X au cours desquels l'humidité relative a été contrôlée, a permis de déterminer les champs de déformation hygroscopiques au travers de l'épaisseur du carton. Ceux-ci présentent de fortes hétérogénéités qui peuvent être reliées à une évolution spécifique de la porosité de certaines couches. Par ailleurs, il est possible de distinguer un comportement différent des couches selon la nature de leurs fibres, fonction des caractéristiques des pâtes chimiques ou mécaniques dont elles proviennent

Development of 100% bio-based and biodegradable women’s sanitary napkins from lignin-rich fibers

International audienc

Ultrasounds welding of nanocellulosic materials

International audienceThe interest for cellulose nanocrystals and nanofibrils is exponentially increased since last decade thanks to their industrialization. In addition to their low density, high aspect ratio, high stiffness and Young’s modulus and chemically reactive surface, this material is well known for its high specific surface. Thanks to these particular properties, cellulose nanomaterials can be used within a wide variety of applications. Coating is one of the promising applications for nanocellulose mainly for barrier applications in packaging. Indeed new bio-based but also high performance solutions are expected in food packaging. Unfortunately, up to now, high barrier solutions can be provided but they always require a layer of thermosealing polymer which is usually fossil based. These multilayer materials are also more complicate to handle when end of life is considered. One solution would be to propose cellulosic materials which could be welded easily. Except thermosealing, ultrasounds welding have been developed in plastic industry last years.This study is a proof of concept that nanocellulosic materials can be welded by ultrasounds. Several nanocellulosic materials were firstly designed and characterized, i.e. from classic cellulose nanocrystals and nanofibrils to functionalized CNC by esterification with lauric acid. Than model films were prepared and welded by ultrasounds. Process parameters were optimized and successful welding were obtained and mechanically characterized. These very positive results have been patented and open the doors for new solutions in welding of biobased materials

Ultrasounds welding of nanocellulosic materials

International audienceThe interest for cellulose nanocrystals and nanofibrils is exponentially increased since last decade thanks to their industrialization. In addition to their low density, high aspect ratio, high stiffness and Young’s modulus and chemically reactive surface, this material is well known for its high specific surface. Thanks to these particular properties, cellulose nanomaterials can be used within a wide variety of applications. Coating is one of the promising applications for nanocellulose mainly for barrier applications in packaging. Indeed new bio-based but also high performance solutions are expected in food packaging. Unfortunately, up to now, high barrier solutions can be provided but they always require a layer of thermosealing polymer which is usually fossil based. These multilayer materials are also more complicate to handle when end of life is considered. One solution would be to propose cellulosic materials which could be welded easily. Except thermosealing, ultrasounds welding have been developed in plastic industry last years.This study is a proof of concept that nanocellulosic materials can be welded by ultrasounds. Several nanocellulosic materials were firstly designed and characterized, i.e. from classic cellulose nanocrystals and nanofibrils to functionalized CNC by esterification with lauric acid. Than model films were prepared and welded by ultrasounds. Process parameters were optimized and successful welding were obtained and mechanically characterized. These very positive results have been patented and open the doors for new solutions in welding of biobased materials

Analysis of the strain and stress fields of cardboard box during compression by 3D digital image correlation.

International audienceCorrugated boards with small flutes appear as good alternatives to replace packaging folding boards or plastic materials due their small thickness, possibility of easy recycling and biodegradability. Boxes made up of these materials have to withstand significant compressive loading conditions during transport and storage. In order to evaluate their structural performance, the box compression test is the most currently performed experiment. It consists in compressing an empty container between two parallel plates at constant velocity. Usually it is observed that buckling phenomena are localized in the box panels, which bulge out during compression [1]. At the maximum recorded compression force, the deformation localises around the box corners where creases nucleate and propagate. This maximum force is defined as the quasi-static compression strength of the box. The prediction of such strength is the main topic of interest of past and current research works. For example, the box compression behaviour of boxes was studied by Mc Kee et al. [2] and Urbanik [3], who defined semi-empirical formula to predict the box compression strength, as well as by Beldie et al. [4] and Biancolini et al. [5] by finite element simulations. But comparisons of these models with experimental results remain rather scarce and limited

Surface stress and strain fields on compressed panels of corrugated board boxes. An experimental analysis by using Digital Image Stereocorrelation.

International audienceThe complex behaviour of corrugated board packages under compression loading is investigated in this work. Original experimental data are obtained by using a Digital Image Stereocorrelation technique for measuring the displacement and strain fields of the panels' outer liner of the tested boxes. The stress field is also estimated by accounting for the anisotropic mechanical behaviour of the outer liner, its residual stress state induced by the processing of the corrugated board and the effects of box manufacturing operations and compression. Results show that these fields are extremely heterogeneous on the panels' surface. Most stressed areas are located along the panels' edges. The elastic limit of the outer liner is reached quite soon during compression. Box geometry and panel flaps are of primary importance on the observed phenomena. This approach delivers useful information to improve kinematic and constitutive assumptions for buckling and post-buckling models of boxes or thin-walled sandwich structures