Effect of calendering on paper surface micro-structure: A multi-scale analysis

Paper is a complex composite material. Its structure and surface greatly influence its end use properties. Calendering is a finishing process applied to paper to provide a shiny surface and to improve the smoothness. Hence, the control of the efficiency of calendering and the characterization of the final product necessitate the measure of the surface modification. Furthermore the relationship between the surface and the obtained level of gloss has to be further developed. The main purpose of this study is to describe the modification of the micro-structure at various scales of the paper surface due to the calendering process (under various processing conditions). The characterization of the paper surface was carried out thanks to an optical device allowing the topographic measurement to be taken at various scales. The equipment combines topographical imaging with a high definition camera, allowing measurement on the exact same area of the sample after each pass in the nip. We therefore introduce a new way to perform multi-scale analysis of the paper surface modification based on fractal theory.