Performance of a final hydrogen peroxide stage in the ECF bleaching of Eucalypt D0EOPD1 kraft pulps

The compromise between reaching pulp target brightness and guaranteeing a high-quality bleached pulp is often difficult to manage because of the nature of the last chromophores present. This study reports the performance of either hydrogen peroxide or chlorine dioxide in a final bleaching stage applied to three eucalypt D0EOPD1 kraft pulps to reach a target ISO brightness of 90±0.5%. The D1 pulps had ISO brightness values of 84.7%, 86.9%, and 88.7% (pulps A, B, and C, respectively). The experimental results revealed that while chlorine dioxide charge was linearly correlated with D1 brightness, a much higher hydrogen peroxide charge was needed to bleach pulp A compared with pulps B and C. All P pulps had lower brightness reversion and better beatability than D2 pulps. In addition, we observed better physical and optical papermaking properties in P pulps (except for tear index for pulp A), although these pulps exhibited lower intrinsic viscosity. Therefore, the best choice for completing that particular ECF sequence is to push chlorine-dioxide bleaching action in D1 until at least 87% ISO brightness is reached, with the purpose of degrading phenolic units as much as possible, and then to advance with peroxide to boost brightness at the cost of quinone destruction.