IMPROVING PROPERTIES OF POPLAR APMP BY MODIFIED PULPING PROCESS

摘要

Changing conventional two stages chemical impregnations into one chemical impregnation before refining and one supplementary bleaching stage after refining in poplar APMP pulping process were studied. Through the comparison of physical properties and beating energy consumption of the pulp obtained from the conventional and the modified APMP pulping process, the optimal conditions of the modified process were: NaOH 4%, H2O2 2%, 50 min, 75°C and liquor ratio 1: 4 in chemical impregnation stage and NaOH 2%, H2O2 4%, 60 min, 70 °C and pulp concentration 10% in supplementary bleaching stage. 4% NaOH in the impregnation stage could soften fibers more effectively and 2% H2O2 could maintain the brightness of pulp and keep off pulp from alkali darkening. 2% NaOH was sufficient to provide alkali environment for peroxide bleaching, and 4% H2O2 enabled obtaining high brightness in the supplementary bleaching stage. The brightness of pulp obtained from the modified APMP process increased 4% ISO. Both the opacity and light scattering coefficient of pulp were improved. The breaking length, tearing index and bursting index of pulp obtained from the modified APMP process increased respectively by 0.5 km, 3% and 13.3%. The synergy of peroxide with alkali in the modified APMP pulping process not only improved the optical properties of pulps, but also enhanced the strength properties. The supplementary bleaching stage could prevent invalid decomposition of hydrogen peroxide in refining process and pulp yellowing, and promote fiber softening to be beaten and fibrillated more easily, reducing beating energy consumptions. Compared with the conventional process, at the same beating degree as 44 °SR, the beating energy consumption in the modified APMP process was reduced by 17%.