Two slurries that consisted of precipitated calcium carbonate (CaCO3) nanoparticles and unbeaten hardwood bleached kraft pulp (HBKP) were prepared via ultrafine bubble and mixing methods. In the ultrafine bubble method, a CO2 gas flow was bubbled into a HBKP slurry that contained Ca(OH)2 to prepare a precipitated CaCO3/HBKP composite slurry. The HBKP/water and precipitated CaCO3/water slurries were prepared separately and mixed to prepare a precipitated CaCO3/HBKP mixture slurry. Each of the two CaCO3/HBKP slurries was separated into five fractions using a tube flow fractionation (TFF) system. The first and second fractions consisted of long HBKP fibers and fiber aggregates. The third fraction had the highest mass ratio of the components in the five fractions, and it had approximately 1-mm-long HBKP fibers. The fourth fraction contained primarily HBKP short fibers and CaCO3 aggregates. Thus, the CaCO3/HBKP components in the slurry were separated adequately by TFF, depending on their hydrodynamic sizes. The average width of each fraction in the CaCO3/HBKP composite slurry was always larger than that of the corresponding fraction from the CaCO3/HBKP mixture slurry, which indicated that precipitated CaCO3 nanoparticles and their aggregates attached stably to long and short pulp fiber surfaces in the composite slurry.
In recent years, the quality of recovered paper has been deteriorated due to an increase of materials to be avoided, such as prints with Ultra Violet(UV)curable ink. The aim of this paper is to develop a method which can easily and promptly distinguish those poor-recyclable prints from recovered paper, and to put the method into practical use in deinked pulp(DIP)mills. In order to achieve this purpose, first, the spectrum data of several kinds of prints were obtained by using the attenuated total reflection infrared spectroscopy (ATR-IR) . Second, the recyclability of those prints was evaluated by lab-experiments. Third, a database was made by correlating the spectrum data and their recyclability, so as to develop the ATR-IR method. Finally, the ATR-IR method was applied to inspection of bales in DIP mills. By examining each print with ATR-IR apparatus, characteristic peaks were detected which helped to determine the type of ink. From the results of lab-experiments, the numbers of dirt speckles in DIPs from UV, UV varnish over coated, and polystyrene over coated prints, respectively, were much higher than those of conventional prints(oil-based ink) . In case of using the ATR-IR method, those prints were distinguished more precisely compared with the conventional solvent detection method used in DIP mills. As for the application of the method for incoming inspection in the mills, it has turned out that there was a certain tendency to decrease incidence rate of dirt troubles in DIP production after the application.
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