On the Effect of Introducing Ozone in ECF Bleaching of Eucalyptus Kraft Pulp, 2011 International Pulp Bleaching Conference

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ZDED and DEDD sequences were applied on an oxygen delignified eucalyptus (mixture of E. Grandis and E. Saligna) kraft pulp from Brazil. When ZDED and DEDD were compared, the displacement ratio calculated as the quantity of pure ClO2 replaced by 1 kg ozone was found between 2.5 and 3.5 kg, as compared to 1.7 kg in theory. This indicates that less useless reactions occur in ZDED sequence. In ZDED, the cellulose viscosity decreased substantially with the increase in the ozone charge (down to 50% at 0.8% ozone) . Other typical characteristics of the ZDED pulps were the easier beating, the lower water retention value (WRV), the higher proportion of kinked fibres and the lower wet zero span breaking length (seen only at 0.8% ozone charge), as compared to DEDD. From a comparison with cellulase and TEMPO treatments it was concluded that the viscosity loss due to the introduction of ozone in an ECF sequence does not translate into a similar loss in strength because the cellulose attack must be rather homogeneous along the fibres. Moreover the appearance of more curls and kinks could be partly attributed to the lower content in carboxyl groups in the ZDED pulps.