Institute of Solid State Physics
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Pore space extraction and characterization of sack paper using μ-CT Paper is a seemingly abundant material. The fact that paper is porous enables a vast number of commercial applications of paper. However, the experimental quantification of its porosity or its pore network properties is difficult and often highly indirect. For sack kraft paper, a direct quantification of the pore space is particularly desirable. By its high porosity and its additional mechanical strength, sack kraft paper often serves as a vital component for packing products, e.g., in cement bags. A non-destructive analysis of the 3D micro structure holds the promise to directly assess the pores. X-ray-microcomputer tomography (μ-CT), frequently with sub-μm resolution, has been established as a method to study the fiber and pore structure of paper. However, it is not established whether the sizes of previously measured paper samples can be considered large enough to account for the inherent inhomogeneity of paper sheets. Here we explore whether we can extract and analyze the pore structure of paper for larger sample areas at a correspondingly lower resolution. The lowered resolution poses a severe challenge for the reliable identification of data voxels as pores or as fibers, because the feature contrast due to X-ray absorption between the paper fibers (made of cellulose) and air is weak. We show that we can reliably assign each data voxel by using a method that relies on the intensity values of the data voxel and its local environment. With the such extracted pores, we can now calculate quantities that are related to the geometry of the pores and their connectivity properties. We address a paper-born challenge for such an analysis, i.e., we cannot always unambiguously tell whether a pore is located inside the paper sheet or at the surface of the paper. The way the paper surfaces are extracted from the microstructure determines decisively the final values of the predicted properties. We demonstrate that the qualitative comparison of the investigated sack kraft paper samples is robust with respect to the choice of the paper surfaces. A true distinction of the samples is only possible when comparing the properties of the pore network. |
