Estimation of microstructural properties from synchrotron X-ray microtomography and determination of the REV in paper materials

The porosity and specific surface areas of four industrial paper materials were determined from synchrotron X-ray microtomography. The porosity profile within the thickness of each paper material shows that a paper sheet consists of three layers: two boundary layers, which present a strong gradient of porosity, and a 'bulk' layer in which the porosity is almost constant. The anisotropy and the heterogeneity scale of the microstructure in the 'bulk' layer was then analyzed by means of covariograms. It is shown that the microstructure of the four studied papers is transverse isotropic and that the anisotropy of papers containing fillers is less pronounced. Finally, the representative elementary volume (REV) for both studied microstructural properties was evaluated using two techniques: a systematic analysis of the influence of the volume size on the property measurement, and a statistical methodology. The REVs given by both methodologies are then compared