Three Dimensional Localization and Visualization of Paper Fines in Sheets

Paper fines are fibrous cellulosic materials capable of passing a 200-mesh screen, grated by processing paper pulp from the extraction of cellulose to the sheet formation. The full impact of fines on paper properties, as e.g. an increase of paper strength, was proven in extensive studies1. However, their distribution inside the paper has not been unraveled s and remains elusive so far. In general, the distribution of smaller cellulose constituents (e.g. fines) was studied in several approaches in the literature but a satisfying model for the 3D distribution in hand sheets has not been established. In our approach, we labelled fines via an in-situ synthesis, coating the surface with iron-cobalt oxide nanoparticles. The coating forms a an almost continuous layer, but the bonding between the paper fibers is not influenced, since mechanical and physical properties of formed sheets do not reveal significant differences to those prepared through addition of non-labelled fines. The labelling affects the X-ray absorption of fines and the nanoparticles show a specific electromagnetic emission spectrum. These can be applied to localize and visualize fines with imaging techniques like X-ray microtomography or energy dispersive X-ray spectroscopy. According to these experiments, the fines are located in the pore walls as well as in between fiber bonds, as already speculated earlier in literature. These results contribute to a better understanding of the distribution of the fines fraction in paper and may lead to new products and applications for paper and board based products.