Analysis of prewetting conditions for old magazine papers before pulping in deinking

Abstract

Recent research on deinking with an old newspaper (ONP)/old magazine (OMG) furnish and with a 100% ONP furnish demonstrates that the ink-substrate bond might not be sufficiently weakened within the short wetting time used in conventional pulping. If enough time for paper wetting is allowed before pulping, better ink detachment could be achieved when compared with conventional pulping. However, it has remained unclear how different prewetting conditions affect ink detachment and fragmentation when processing OMG-based furnish, such as supercalendered (SC) and lightweight coated (LWC) papers. In this study, we investigated the influence of prewetting time, temperature, and chemistry on the optical properties of rotogravure printed SC and heatset offset printed LWC-based pulps, when prewetting is performed without mechanical action before the actual pulping process. Different prewetting times (0-24 h) and temperatures (25°C-65°C) were tested with conventional alkaline soap chemistry and with reduced alkaline soap chemistry. The results for SC pulp support earlier findings and reveal that ink detachment can be improved by wetting SC paper with conventional deinking liquor before pulping. With SC paper, the longer the prewetting time, the lower the amount of attached ink after pulping. Ink that is printed on a coating (LWC paper) is easily detachable; therefore, its release cannot be improved by prewetting. Ink fragmentation was similar with and without prewetting treatment for SC- and LWC-based pulps.