Cooks with high and low levels of hydroxide ions and hydrosulfide ions were carried out to two different kappa number levels.The pulps were bleached by two difference ECF sequences,OD(EOP)DnD and OD(EOP)DR A higher concentration of hydroxide ion was found to give a brighter unbleached pulp and a somewhat higher final brightness after each bleaching sequence.A higher level of hydrosulfide ion did not give a higher unbleached brightness,but it led to better brightness development during bleaching.The final kappa number was not critical for the final bleached brightness,but an increase in cooking kappa number from 16 to 22 gave a 17% increase in chlorine dioxide consumption in the OD(EOP)DnD sequence.The humid brightness reversion correlated with the HexA content after bleaching,but the dry brightness reversion did not correlate with any of the studied parameters.For the humid atmosphere,a final D stage gave less brightness reversion than a final P stage gave,but the reverse was true for the dry atmosphere.
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