| In attempt to reduce thermally induced and photo-induced brightness reversion (yellowing) of aspen BCTMP, chemical additives were sprayed on dry handsheets prior to photo-irradiation or exposure to high temperature and humidity. It was shown that a combination of inhibitors including a radical scavenger, chromophore modifier, UV absorber (UVA), and chelating agent were more effective than any single-component inhibitor. While combinations of UVAs, radical scavengers, and chromophore modifiers have been previously reported to give good brightness stability, the addition of a chelating agent was here shown to provide further benefit.; A novel application method for yellowing inhibitors is also presented in this study. Inhibitors were loaded on zeolite molecular sieves, which were then added to the pulp slurry. Inhibitors remained adsorbed to the zeolites and were thus retained by pulp fibers during sheet formation. This allows for convenient wet end addition of yellowing inhibitors, a universally applicable application method. |
