Bleaching of eucalypt kraft pulp with peracids -: the effect on pulp characteristics

Peracetic acid (Pa), peroxymonosulfuric acid (Px), and their mixture (Pxa) were used in the Elemental Chlorine Free (ECF) and Totally Chlorine Free (TCF) bleaching of an oxygen pre-delignified eucalypt kraft pulp (kraft-O). For ECF sequences, peracids were used to replace chlorine dioxide in the D-1 stage and for TCF sequences they were used to replace hydrogen peroxide in the Eop stage. ECF bleaching was carried out to 90% ISO brightness whereas TCF was carried. out to 86 to 88% ISO. ECF bleaching produced pulps with lower Kappa numbers in relation to TCF. The use of peracids increased brightness reversion in the ECF bleaching but decreased it in the TCF bleaching. Pulp viscosity was negatively affected by the peracids both in ECF and TCF bleaching. There were practically no differences in the physical-mechanical properties among pulps bleached by the various bleaching sequences, indicating that peracids were not harmful to cellulose fibres under the conditions used. These results indicated that Pa, Px and Pxa could be successfully used in ECF and TCF bleaching of kraft-O pulps, achieving acceptable brightness without damaging pulp quality.