To investigate the effects of multistage ozone bleaching on strength characteristics of pulps, unbleached kraft pulps of red pine and beech were bleached at 30°C and 02°C by ozone with three times repetition of bleaching and subsequent water wash. The chemical properties and strength characteristics resulted were compared with those of the above pulps bleached by ozone in single-stage and CEHDED, respectively.
The zero span breaking length (m) imparted by three-stage ozone bleaching at 30°C and 02°C were 9, 560 and 11, 693 in unbleached red pine pulp with 310 ml in C. S. F. and 6, 900 and 8, 362 in unbleached beech pulp, respectively. In comparision, the corresponding values given by one-stage ozone bleaching and CEHDED were 5, 352 and 11, 103 in the former pulp and 5, 485 and 11, 110 in the latter one, respectively.
The effective results shown in the above example is likely due to lower degradation of both cellulose and hemicellulose in three-stage ozone bleaching at 02°C.
