3D-oriented fiber networks made by foam forming
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In industrial applications, such as paper and nonwovens, cellulose fibers are used in the form of a network where the fibers are oriented more or less in the sheet-plane direction. However, in many biological systems, fibers are instead oriented in a three-dimensional (3D) space, creating a wide variety of functionalities. In this study we created a 3D-oriented fiber network on the laboratory scale and have identified some unique features of its structure and mechanical properties. The 3D fiber network sheets were prepared by using foam-forming as well as modifying consolidation and drying procedures. The fiber orientation and tensile/compression behavior were determined. The resulting sheets were extremely bulky (above 190 cm3/g) and had extremely low stiffness (or high softness) compared to the reference handsheets. Despite this high bulk, the sheets retained good structural integrity. We found that a 3D-oriented fiber network requires much less fiber-fiber contact to create a connected (“percolated”) network than a two-dimensionally oriented network. The compression behavior in the thickness direction was also unique, characterized by extreme compressibility because of its extreme bulk and a long initial increase in the compression load as well as high strain recovery after compression because of its fiber reorientation during compression.
Keywords3D fiber network Foam forming Percolation Compression
This study was partly financed by the European Regional Development Fund EU-Mål 2, and the authors acknowledge the financial support. The authors also acknowledge various support and help provided by Staffan K. Nyström, Håkan Norberg, and Jan Lövgren from Mittuniversitetet and by Rickard Boman from SCA R&D Centre, Sundsvall. Prof. Bo Westerlind of Mittuniversitetet and Kent Malmgren of SCA R&D are also acknowledged for stimulating discussions and suggestions during the course of this study.
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