Bagasse alkaline sulfite-anthraquinone (AS/AQ) pulping and totally chlorine free (TCF) bleaching

Alkaline sulfite/anthraquinone (AS/AQ) pulping and totally chlorine free (TCF) bleaching of bagasse was investigated. Depithed and wet cleaned bagasse was collected from the Pars Paper Company in southern Iran, dried and then pulped. The active alkali charge was chosen between 16 and 20% on oven-dry bagasse and the alkali ratio, Na₂SO₃/NaOH, was varied from 30/70 to 70/30. The AQ dose was kept constant. While keeping a constant cooking time at maximum temperature for 60 min, the maximum temperature was varied between 155 and 165°C. For bleaching, a pulp with a kappa number of 8.5 was produced under the following conditions: 18% active alkali, alkali ratio 30/70, 60 min cooking at 155°C. TCF bleaching was performed with oxygen and hydrogen peroxide. Oxygen delignification (O) with an alkali charge of 2% NaOH resulted in 50% degree of delignification. A brightness of 80% ISO was achieved with a chelating treatment (Q) and a subsequent oxygen reinforced peroxide bleaching stage (OP) under drastic conditions (4% H₂O₂, 2.75% NaOH, 90 min at 98°C). With an additional peroxide bleaching stage charging 2% H₂O₂, the brightness could be further improved to 83.5% ISO. Bleaching led to only small losses in tensile and burst strength at unchanged tear strength. Short beating in a Jokro mill was sufficient to attain good pulp strength. The results indicate that AS/AQ pulping and TCF bleaching can be successfully applied to bagasse to produce pulp for writing and printing paper.