MODELLING THE PAPER SHEET STRUCTURE ACCORDING TO THE EQUIVALENT PORE CONCEPT

Paper is basically a spatial network consisting of fibres, fines and possibly fillers with partly connected voids in between. The three-dimensional paper structure controls most of the actual paper properties directly or indirectly. However, little is known of the paper structures three-dimensional features at a microscopic level and how this in detail influences the macroscopic paper properties. With present microscopy techniques, image analysis and paper structure modelling theories, it is possible to investigate the microscale paper structure and its influence on the physical laws governing the macroscopic behaviour. Phase-contrast x-ray microtomography followed by complex image processing are used for acquiring binary three-dimensional images of paper with a resolution around 1 µm. Information is retrieved from the paper structure applying image analysis for determining the mean pore secant in several directions (θ,ϕ) and the equivalent pore theory to represent the average microscopic features into a macroscopic model. Results show that the proposed ellipsoidal shape representing the homogenised macroscopic pore-fibre interface can be found from the binary three-dimensional paper structure. Having established the ellipsoidal geometry, the equivalent pore concept is applied for modellin