Abstract
Corrugated cardboard is an ecological material, mainly because, in addition to virgin cellulose fibers also the fibers recovered during recycling process are used in its production. However, the use of recycled fibers causes slight deterioration of the mechanical properties of the corrugated board. In addition, converting processes such as printing, die-cutting, lamination, etc. cause micro-damage in the corrugated cardboard layers. In this work, the focus is precisely on the crushing of corrugated cardboard. A series of laboratory experiments were conducted, in which the different types of single-walled corrugated cardboards were pressed in a fully controlled manner to check the impact of the crush on the basic material parameters. The amount of crushing (with a precision of 10 micrometers) was controlled by a precise FEMat device, for crushing the corrugated board in the range from 10 to 70% of its original thickness. In this study, the influence of crushing on bending, twisting and shear stiffness as well as a residual thickness and edge crush resistance of corrugated board was investigated. Then, a procedure based on a numerical homogenization, taking into account a partial delamination in the corrugated layers to determine the degraded material stiffness was proposed. Finally, using the empirical-numerical method, a simplified calculation model of corrugated cardboard was derived, which satisfactorily reflects the experimental results.
Highlights
Paper and cardboard are made of cellulose fibers that mainly come from trees
In the experimental part of our study, four corrugated boards of different grammage were selected and tested, namely, two B flutes: 285 g/m, (B‐285), 410 g/m (B‐410) and two C flutes: 340 g/m (C‐340), 440 g/m (C‐440). Those corrugated boards were subjected to a series of measurements and laboratory tests to check: (a) sample thickness before and after crushing—THK and THK2; (b) sample resistance to edge crushing–ECT; (c) bending stiffness in machine direction (BNT–MD) and in cross‐direction (BNT–cross direction (CD)); (d) shear stiff‐
In the experimental part of our study, four corrugated boards of different grammage were selected and tested, namely, two B flutes: 285 g/m2, (B-285), 410 g/m2 (B-410) and two C flutes: 340 g/m2 (C-340), 440 g/m2 (C-440). Those corrugated boards were subjected to a series of measurements and laboratory tests to check: (a) sample thickness before and after crushing—THK and THK2; (b) sample resistance to edge crushing–ECT; (c) bending stiffness in machine direction (BNT–MD) and in cross-direction (BNT–CD); (d) shear stiffness in machine direction (SST–MD) and in cross-direction (SST–CD); and (e) torsion stiffness in machine direction (TST–MD) and in cross-direction (TST–CD)
Summary
Paper and cardboard are made of cellulose fibers that mainly come from trees. Some of the fibers circulate repeatedly in the production-recycling loop. The material is, environmentally friendly, but the quality of the produced material from recycled fibers iteratively declines. This requires a deeper understanding if one wants to optimize the product and at the same time keep the material eco-friendly. The particular orientation of the fibers resulting from the cardboard production process causes the material to have different mechanical properties along the mutually perpendicular directions. Such materials are called orthotropic materials, as opposed to isotropic ones, which exhibit the same physical properties independent of the direction. The material orientation along the fibers that follow the direction of the web during production is called the machine direction (MD), the direction perpendicular to it is called the cross direction (CD)
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