EFFECT OF LAST STAGE BLEACHING WITH PERACETIC ACID ON BRIGHTNESS DEVELOPMENT AND PROPERTIES OF EUCALYPTUS PULP

Abstract

Investigation of last stage bleaching with peracetic acid is the main subject of this paper. Proper conditions were established to apply peracetic acid as the last bleaching stage of the D(Ep)D/Paa, DHT(Ep)D/Paa, A/D(Ep)D/Paa, DHT/Q(PO)Paa and Z/ED/Paa sequences. In addition, the impact of last stage bleaching with Paa on pulp refinability and strength properties was determined. Peracetic acid was consumed relatively fast when applied as the last stage of ECF bleaching sequences. A reaction time of 120 min at 75 oC and pH 5.0 is seemingly adequate regardless of the Paa dose, in the range of 1-5 kg/odt pulp and bleaching sequence. The optimum dose of Paa depends upon the sequence under investigation. In general the Paa application as last bleaching stage caused slight decrease in pulp viscosity, kappa number and HexA content but had no significant effect on pulp reversion and L*a*b* coordinates. The refinability and bonding strength properties of the pulps bleached with the sequences DHT(Ep)DD and DHT(Ep)D/Paa were quite similar when the pH of the last bleaching stage of both sequences were near 5. These properties improved slightly when Paa bleaching pH was raised to 8.5.

Keywords

• Peracetic acid
• Bleaching
• Eucalyptus pulp
• Physical-mechanical properties