ECF bleaching of eucalyptus camaldulensis kraft pulp with pressurized peroxide stage

The objective of this research was to study the efficiency of pressurized peroxide (PO) stage in ECF bleaching of eucalyptus kraft pulp and compare it with conventional ECF bleaching. Oxygen delignified Eucalyptus camaldulensis pulp was delignified in DE(p)Q (PO) sequence, where temperature, peroxide charge and alkali charge of pressurized per-oxide stage were variables. Brightness, viscosity and yield of bleached pulp and tensile and tear strength of paper made from selected pulps were determined. Results were compared to each other and to reference (DEDED bleached) pulp. All pulps reached full brightness (>88% ISO). Temperature had biggest impact on brightness. Increment of alkali charge at low alkali charge level increased brightness more than further increment of alkali charge or increment of peroxide charge. Lowest brightness from higher temperature and highest brightness from lower temperature were on same level with reference pulp. Reference pulp had higher viscosity and yield than (PO) -bleached pulp. High alkali charge with higher temperature reduced yield and viscosity more than increase in peroxide charge. Pulps bleached with (PO) stage were more difficult to beat than reference pulp. There was not essential difference in beatability among peroxide treated pulps. (PO) bleached pulps were not as strong as reference pulp measured as tear/tensile strength relationship. Higher temperature in (PO) stage increased strength slightly. Influence of chemical charges on strength was not clear.