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You are here: Home > Technique > Processes > Scientific report of the LGP2 > Paper physics > Structural characterisation of fibrous materials           Update: February 26th 2007
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Researchers of the LGP2 (EFPG, INPG, CNRS, CTP)
(November 2006)
 
Documents taken from the
"Scientific Report of the Laboratory of Pulp and Paper Science and Graphic Arts - UMR 5518
Grenoble - France
January 2002-November 2005"

III - Paper physics

III - 2 - Structural characterisation of fibrous materials

Sabine Roland du Roscoat, Xavier Thibault, Yves Chave, Jean-Francis Bloch

The influence of unit operations involved in paper production on its fibrous structure allows the optimisation of the process and to improve the end use properties of paper and board.
Experimental technique have been developed in order to characterise the material structure at a fine scale. However, it is necessary to use a non destructive tool which will not modify the material.

The classical technique of cross cutting and the following observation on a microscope has to be used carefully, as the samples may have been damaged. We has recently the possibility to access a new experimental technique: X-Ray microtomography.

It allows the visualisation of the structure of a porous medium at a 1 micron resolution. 2 PhD thesis have been defended (N. Reverdy-Bruas and X. Thibault) obtaining the first results on the characterisation of paper and felt, respectively. The originality of these works was also to study the influence of the strain on the structural properties and specially on the fibrous distribution anisotropy. These evolutions were correlated to the measurement of permeability tensor, taking into account the deformation of the materials.

A PhD thesis (S. Rolland du Roscoat) started recently aiming to characterise the three dimensional structure of fibrous media, in collaboration with the European Synchrotron Radiation Facility (ESRF). The analyse at the microscale of the fibrous structures of papers and boards constitutes the main aim of this project. This work is motivated by the limitation of existing tool and the industrial interest for such information.

Furthermore, we may split using image analysis the fibres from fillers such as calcium carbonate. These original results leads to the profile of fillers in the bulk of the studied materials. Moreover, we obtained the ranulometry of the considered fillers. The quantitatives results have been validated both on handsheet and industrial papers.

Consequently, it allows the spatial repartition of fillers in the 3D structure and also the optimisation of the end use properties of papers. The objective is first to image the studied structure at the defined scale. Then, it is necessary to filter the raw data in order to weaken the experimental noice. Specific software have been necessary and developed in this context. Finally, a segmentation technique has been implemented on the obtained 3D images.

It is important to note that these mathematical techniques were carried out on 3D objects. Hence, the classical 2D treatments are not efficient in the studied cases. Consequently, objects (fibrous structure) may be extracted from the grey level images. Then, the identified fibrous structure is obtained and may be analysed. The results concerns for exmaple the two-sideness effect. The anisotropy gradient may also be obtained.
We were involved in a international long term project. Hence, we were able to access periodically to beam time at ESRF. Moreover, a project, in the framework of a collaboration with the Rhône-Alpes region, different laboratories and industrial partners, were put accross, aiming to the characterisation of papers. Moreover, the simulation of physical properties is developed concerning permeability or thermal properties, for example.
A PhDThesis (M. Decain) has begun in this context aiming to validate the simulation from the obtained 3D structures.

Reconstructed mono base felt   Reconstructed mono base felt
Figure 1 - Reconstructed mono base felt using X-SRmCT technique.
On left, the whole volume is 3.8 mm wide and 2 mm thick.
On right, the reconstructed base of the felt is 3.8 mm wide and 0.8 mm thick.
Example of segmentation   Example of segmentation
Figure 2 - Example of segmentation.
On left, grey levels
On right,  black (air) and white (fibres and yarns).
 
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