Chlorine dioxide bleaching of nineteen non-wood plant pulps

Bleaching of unbleached and oxygen delignifled pulps from nineteen non-wood plants has been evaluated in elemental chlorine free bleaching. Chlorine dioxide charge (kappa factor 0.15, 0.20 and 0.25) and temperature (70 and 85 degrees C) in the delignification stage (D) were varied. Chlorine dioxide (ClO2) charge and temperature exhibited lower kappa number and higher brightness after alkaline extraction (EP) stage. High temperature ClO2 delignification (D-HT) exhibited higher final pulp brightness. The final brightness of wheat straw pulp reached to 90 % after D-0/D-HT (EP)D-1 bleaching, while banana pseudo stem pulp showed the worst bleachability. Residual hexeneuronic acid contents in final pulp from most of the nonwood plants were lower and exhibited 1-2 % higher pulp brightness in D-HT process than D-0 process. Oxygen delignified pulp and D-HT process discharged lower COD load.