TOTALLY CHLORINE FREE (TCF) BLEACHING OF WHEAT STRAW SODA-ANTHRAQUINONE PULP

摘要

Totally chlorine free (TCF) bleaching of wheat straw soda-anthraquinone (AQ) pulp was investigated. Previous pulping experiments,performed under different conditions had revealed that soda-AQ pulping with 16% active alkali for 90 minutes,at 160 °C,yields pulp suitable for bleaching experiments. TCF bleaching was performed in an O Q (OP) or O Q (OP) P sequence.Oxygen delignification with an alkali charge of 2.5 % NaOH at 90 °C and 90 min resulted in a delignification rate over 50 %.In the subsequent (OP) stage,drastic conditions (4% H2O2,2.75% NaOH,90 min at 98 °C) were required to exceed an 80% ISO brightness.With a final P stage,brightness could be improved to 84-85% ISO.Bleaching led to only small losses in tensile and burst strength for unchanged tear strength.Short beating in a Jokro mill was sufficient to attain a breaking length well above 7 km. The results of the study indicate that TCF bleaching can be successfully applied to wheat straw soda-AQ pulps to produce pulp for writing and printing paper without detrimentally affecting the environment.