TCF bleaching of eucalyptus kraft pulp: The selection of the sequence and the best conditions

Bleaching was conducted with conventionally oxygen-delignified pulp. The residual lignin was lowered either with an OAqZO or an OAqPeracidO treatment. Kappa numbers between 3 and 5 were achieved without any viscosity penalty. The bleachability was better after ozone activation. A concentration of 0.25% ozone was more effective than 1.5% peracetic acid Final brightness was above 90% ISO at similar strength properties. Final bleaching with hydrogen peroxide was made with only one stage. The addition of magnesium sulphate and sodium silicate improved the results. The lowest hydrogen peroxide demand resulted at temperatures below 100 degrees C with a retention time of up to 24 h. The 90% ISO brightness level needed an input of less than 2% H2O2. Bleaching at 110 degrees C accelerates the reaction, but yields inferior results in terms of peroxide consumption and viscosity.