Effect of natural aging on the oxidative and reductive bleaching of the deinked Pulp

The present study was aimed to investigate the effect of natural aging on the optical (brightness, yellowness, opacity) and strength properties (tensile index, burst index, tear index) of the mixed Old Newspaper (ONP)/ Old Magazine (OMG) deinked pulps, bleached with oxidative and reductive bleaching agents. In this research local Offset-printed ONP and OMG (especially derived from Mechanical pulp or Chemical-Mechaical pulp) were naturally aged for five months, then deinked by flotation and bleached with Hydrogen Peroxide (H2O2) and Formamidine Sulfinic acid (FAS) in both single-stage and two-stages bleaching operations. Result showed that natural aging caused the brightness value and all strength indices to decrease and the opacity and yellowness values to increase, compared to those of the newly recycled papers without aging. Therefore, it should be avoided as far as possible. In addition, reductive bleaching (using FAS) was found more effective than oxidative bleaching (using H2O2) in improving all optical and strength properties of the hand-sheets. Also, in two stages bleaching sequences, it was observed to be most appropriate to use FAS as the latter bleaching chemical after H2O2. Thus, it can be totally concluded that application of the reductive bleaching system (by FAS) is apparently more effective and efficient than oxidative bleaching system (by H2O2) in both single-stage and two-stages bleaching operations of the deinked pulps from Offset-printed wood-containing recycled papers in terms of the optical and mechanical properties.