3D synchrotron X-ray microtomography for paper structure characterization of z-structured paper by introducing micro nanofibrillated cellulose

International audience; A layer of Micro Nanofibrillated Cellulose (MNFC) was added during the formation of TMP paper to create a z-structured paper. A MNFC layer was added either on the top or in the middle of the thickness of a TMP sheet using a Dynamic Sheet Former. The MNFC layer basis weight was varied from 2 to 20 g.m-2 for a final paper basis weight of 60 g.m-2. 3D images of the paper structure were obtained by Synchrotron X-ray microtomography, showing that localized MNFC fibrils were retained in the paper structure. The small dimensions of CNF, particularly in width, and the presence of the calcium carbonate in the MNFC layer permit to clearly differentiate the TMP fibers from the MNFC fibrils. The porosity profiles for 100% TMP sheet and 100% MNFC film present a constant internal bulk porosity at about 75% and 38%, respectively. Porosity profiles of the z-structured paper display the presence of 2 or 3 different porosity zones in the internal bulk region. These results confirm the possibility to design papers with targeted porosity gradients in the z-direction without paper post treatment.