The aim of this study was to compare different bleaching alternatives for oxygen delignified eucalyptus aimed at a low brightness reversion. Three eucalyptus pulps with different characteristics were included in the study. D (OP) Dn D, D
∗ (OP) Dn D, A
∗D (OP) Dn D and Z (OP) Dn D bleaching sequences were compared, and the corresponding sequences with a final P stage instead of a final D stage were also included. Brightness reversion in both dry and humid conditions before and after beating was evaluated. Other important parameters such as bleaching chemical demand, pulp viscosity and fiber strength potential were also considered.
When bleaching to 90.5% ISO brightness and compared to the standard D pre-bleaching, D
∗ gave 5-17% savings in OXE, A
∗D gave 16-24% savings, Z at a high ozone charge (about 5.0 kg⁄t) gave a small saving (4%) for the traditional E. globulus pulp but increased the OXE consumption with 13-31% for the two other pulps. A considerable increase in chemical demand was recorded at a low ozone charge where also the brightness target was difficult to meet. The standard D sequence gave the highest and the Z sequence the lowest viscosity. The standard D sequence also showed the highest fiber strength potential measured as rewetted zero span strength at 3000 PFI revolutions, and again the Z sequence gave the lowest value.
The different pre-bleaching alternatives gave only small differences in dry brightness reversion and the results after beating were different from those prior to beating. A final P stage always gave better dry brightness reversion than a final D stage. The standard D sequence gave higher humid brightness reversion values than the other sequences, but modifications to the D sequence showed promising results. Evaluation of brightness reversion in humid and dry atmospheres gave different results and there was no general correlation between the two evaluation methods.
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