Environmentally Friendly Processes for Bleaching of Secondary Fibers, 2002 Fall Technical Conference

This study was aimed at developing low environmental impact technologies for bleaching four secondary fiber samples, namely: (1) a sample of kappa 7.3 and 66% ISO brightness (2) a sample of kappa 14.4 and 55.1% ISO brightness, (3) a sample of kappa 26.6 and 70.4% ISO brightness and (4) a sample of kappa 69.8 and 42.4% ISO brightness. The samples (1) and (3) were bleached with TCF sequences (totally chlorine free) and samples (2) and (4) were bleached with TCF and ECF (elemental chlorine free) sequences. The results were interpreted on the basis of overall process yield, bleaching chemical requirements and costs to achieve 78-82% ISO brightness, and pulp quality measured by color coordiante b*, fluorescence, viscosity and kappa number. It was determined that the most suitable bleaching sequence for samples (1) and (3) is the (ZQ)(PO). This TCF sequence reached the brightness target at reasonable costs for sample (1) but at prohibitive costs for sample (3). The most suitable TCF sequence with ozone for sample (2) was the Q(PO)(ZQ)(PO). This sequence results in high brightness ceiling and bleached pulp of low color although of high fluorescence. On the other hand, the TCF sequence without ozone best suited for sample (2) was the Q(PO)Q(PO) which is of lower capital investment as compared to the TCF with ozone. The most attractive ECF sequence for sample (2) is the DEDD. This sequence results in high brightness and low cost besides eliminating pulp color and fluorescence. It was not possible to bleach sample (4) to the brightness target using TCF technologies, being the sequence AQ(PO)QPP the one of highest potential for this sample. Besides not reaching the brightness target this sequence shows low yield and do not remove pulp color. The target brightness was reached on sample (4) with the ECF sequence DEopDEDP but at the expense of high chemical costs and yield losses.