Based on the powerful non-destructive 3D microscopic imaging capability of X-ray CT scanning technology, and combined with the digital image processing method, this study developed the three-dimensional structural model of filled paper, visualized the distribution of filler, and conducted the permeability simulation of filled paper.

Initially, short cotton fiber and precipitated calcium carbonate (PCC) filler were used as raw materials, two types of fillers of PCC1 (4.15 µm) and PCC2 (5.45 µm, preflocculated PCC1) were applied respectively, and two kinds of hand-made paper sheets with the same basis weight (105±1 g/m²) were manufactured accordingly. After the scanning of X-ray CT equipment, the obtained CT images were pre-processed by Otsu algorithm to separate the parts of fiber, pore and filler in the images. Next, the three-dimensional structural models of the filled paper sheets were developed by the software of Avizo. The sizes of Representative Elementary Volume (REV) were determined preliminarily for decreasing computation load. Subsequently, the pore network models were established, and the parameters of porosity, tortuosity, filler particle size and the spatial distribution of pore space were extracted. Finally, based on the developed structural model, liquid permeation simulations were carried out on the horizontal and thickness directions of the filled paper, to study the effects of the particle size and spatial distribution of fillers on the three-dimensional pore structure and permeability of filled paper.