Non degrading TCF bleaching sequences including an ozone stage for hardwood and softwood kraft

Various chemical pulps (hardwood, softwood, kraft and sulphite) were delignified by ozone. No difference in efficiency or in selectivity was observed, which suggested that no matter its chemical structure, lignin is far more reactive with ozone than carbohydrates. OZP sequences have been performed to reach full brightness. Most of the cellulose degradation took place during the P stage. Several ways were found to reduce this degradation: reduction of the carbonyl groups formed during Z, chelation of the metals before P and addition of Mg2+ in P, led, when performed together, to satisfactory protection of cellulose and maintained pulp quality. Some of these improvements were not necessary in the case of hardwood pulps.