Simulation of Particle Packing for Modelling the Light Scattering Characteristicsof Paper

摘要

When an analysis of the optical properties of paper is needed, the mostfrequently used theory is the Kubelka-Munk theory. However, it fails to be useful when a separate analysis of the effects of the optical properties of a single particle and of the sheet structure is required. In this study a simulation model for calculating optical properties of paper is proposed. The simulation model introduces a new parameter i.e. the void probability, to be used for counting the number of voids in a cross section of paper. The results suggest that the number of voids indeed provide an adequate description of the sheet structure for optical calculations. In order to describe the scattering properties of a single particle, the simulation model uses the so called plate model. In the study theoretical considerations suggested that even though the plate model lacks the theoretical exactness, it is accurate enough to provide a way to relate the optical parameters of the particles to the optical properties of the sheet. In the simulation model then, paper structure is depicted by arranging model particles. The packing of these particles is controlled by using the void probability. To verify the concept of void probability, an image analysis technique was used to measure the number of voids in paper sheets. The good agreement between measured and calculated values suggests that the concepts of the model as well as the model approximations are valid. The thesis discusses the fact that the one-dimensional treatment used in the simulation model may not be an adequate description for a real three-dimensional light scattering phenomenon. It should, however, be recognized that as one-dimensional approximations the developed simulation model and the Kubelka-Munk theory are both equally accurate. This thesis reviews also two applications both illustrating how the simulation model provides new possibilities to a paper scientist to explain his optical observations based on the interpretations of the sheet structure.