The aim of this work was to develop methods for describing the porosity, martens micro hardness and the surface roughness of ribbons. Ribbons were manufactured from different types of celluloses (microcrystalline celluloses, powder celluloses) and were produced on different roller compactors (Mini Pactor™, Macro Pactor™50, Macro Pactor™100; Gerteis AG, Switzerland) by using specific compaction forces from 2 to 20 kN/cm. Due to the irregular shape of ribbon pieces, a mathematical calculation of the density or porosity of a ribbon from its dimensions and weight is impracticable. Thus, following methods to determine the porosity were developed: 1. The application of a method which is based on the buoyancy principle (buoyancy method); 2. The application of a modified geometrically method which regards punched parts of a ribbon (punch method). 3. The application of a spectroscopic method which evaluates the absorption of NIR-light (NIRS method). For describing the properties of the ribbons concerning to their martens micro hardness and surface roughness, a micro hardness testing instrument (Fischerscope H 100) and a surface profile analyzing instrument (Hommeltester T2000) were objects of the interest. For each method the limitations and the application were discussed and compared regarding to their accuracy of statements, their reproducibility and their expenditure of material and time consumption. In general, the porosity within the ribbons varies regarding to the border areas in comparison to the ribbons middle parts. Thus, in dependence on the different principles of the methods, the results differ from each other. A directly comparison of the results is not possible. The buoyancy method offers the best possibility to comprehend the porosity as an integral property of the whole ribbon. In contrast, the punch method and the NIRS method ignore the outer areas of the borders. Therefore, the determined porosity values are lower than those obtained from the buoyancy method for the same ribbons. Their use is indicated when analyzing crumbling or breaking ribbons. All methods showed plausible results. When increasing the degree of densification all methods detected the decreasing of the porosity reproducibly. In the case of determining the surface roughness or the micro hardness, ribbons should be dedusted in all cases. The ribbons were investigated at different parts across and also along the ribbon. Thereby systematically dependencies on the profiles from used compaction forces were obtained in all cases. The results of surface roughness correlate with those of the micro hardness: a higher micro hardness corresponds with a smoother surface and in turn correlate with the used specific compaction force. All methods allowed the detection of inhomogeneity of ribbons, which is caused by the kind of used sealing system: Using the seal side inliner the middle parts of the ribbons showed a higher micro hardness and a more pronounced evenness than the border areas. In summary, it can be concluded, that now a characterization of ribbons become possible through the methods described in this work. |