THE EFFECT OF HYDROGEN PEROXIDE CONTAINING FILTRATES AND STORAGE ON UNBLEACHED AND BLEACHED PULP BRIGHTNESS

摘要

The correlation between unbleached and bleached brightness are not always good in the stone groundwood (SGW) hydrogen peroxide (H2O2) bleach line at the Kvarnsveden Mill. If the variation in unbleached brightness is a function of the wood raw material or the fiber separation/development process, the bleached brightness should correlate with the unbleached brightness. However, when recirculation of H2O2-containing filtrates influences the unbleached brightness, the correlation to bleached brightness might be lower. The effect of recirculation of H2O2-containing filtrates and pulp storage was therefore investigated in two studies using Norway spruce mechanical pulps. One study showed that the increase in unbleached brightness as a result of storage with residual H2O2 present resulted not in higher brightness after H2O2 bleaching, it was the opposite. Probably both darkening and bleaching reactions occurred during pulp storage with residual H2O2 present, resulting in a pulp that was more difficult to bleach. The other study showed further that approximately the same brightness was reached after H2O2 bleaching in spite of which liquor the pulp was diluted with before storage although the unbleached brightness was very different. The effect of residual hydrogen peroxide and storage on unbleached brightness is probably the reason for the poor correlation between unbleached and bleached brightness in this bleach line.