Use of Ozone in a Last Bleaching Stage, 1996 Pulping Conference Proceedings

Christine Chirat

Technique du Papier

François Lambert & Dominique Lachenal

Ecole Française de Papeterie

Christian Coste

Degrémont

Ozone can be used as a “polishing” stage at the end of bleaching sequences. DEDEDZ, ODEDZ, OQP(PO)Z and OZPZ sequences were studied in this respect. Several points in brightness could be gained with charges in ozone comprised between 0.1 and 0.4% on pulp, with no significant loss in viscosity, nor in the strength properties, and with still a good brightness stability. The bleaching sequence preceding the final Z stage had an influence on the brightening ability of the Z stage which would be related to the nature of the remaining lignin or chromophores in the different pulps. The final Z stage did not necessarily have to be carried out in acidic conditions, which is of high practical interest. A comparison with other reagents in a final stage, such as chlorine dioxide and hydrogen peroxide, showed that ozone can be considered as a good brightening agent and may compete with them.