TCF High-Brightness Bleaching NaOH-AQ Pulp of Fast-Growing Poplar with Low Kappa Number

Abstract

In the paper, technological conditions suitable for H2O2 strengthened oxygen delignification of fast growing poplar NaOH-AQ pulp with low kappa number (Kappa number 13.5, viscosity 851ml/g, brightness37%ISO) were investigated, based on which (Q/OP) QP Totally Chlorine Free (TCF) bleaching sequence was studied, and the TCF high-brightness bleaching of NaOH-AQ pulp with low kappa number was realized. Conditions better suitable for (Q/OP)QP bleaching of NaOH-AQ pulp with low kappa number are as follows: at the stage of H2O2 strengthened oxygen delignification: pulp consistency 10%, alkali dosage 2.5%, H2O2 dosage 3%, MgSO4 dosage 0.5%, oxygen pressure 0.6Mp, temperature 100°C, time 60min; at Q stage: pulp consistency 8%, DTPA 0.3%, initial pH value 4, temperature 70°C, time 120min; at P stage: pulp consistency 10%,H2O2 dosage 2%, MgSO4 dosage 0.5%, Na2SiO3 dosage 0.7％, temperature 70°C, pH value 12, time 120min. With this sequence, the pulp can be bleached with brightness of 82.0%ISO, viscosity 716ml/g, and the bleached pulp yield ratio 91.78％.