Bleaching of Eucalyptus Kraft Pulps with Chlorine Dioxide: Factors Affecting the Efficiency of the Final D Stage, 2011 International Pulp Bleaching Conference

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The bleaching efficiency of the final D stage in the D₀(EP)D₁D₂ bleaching sequence was investigated focusing on the effect of pH in relation to the bleaching history of pulp samples. The pulps used were unbleached kraft Eucalyptus grandis pulps with a kappa number of 14.8, and the same pulp oxygen-delignified to kappa numbers 12 and 9.8. The samples were bleached according to the D₀(EP)D₁ sequence to a brightness of about 86 % ISO and then submitted to the final D2 stage under identical conditions. The target final brightness was 90.5 % ISO. Changes in the kappa number, brightness, viscosity and contents of hexenuronic acid (HexA), 4-O-methylglucuronic acid and the total amount of carboxylic acid groups in pulps were monitored during the bleaching sequence.