PERFORMANCE OF A FINAL HYDROGEN PEROXIDE STAGE IN DIFFERENT ECF BLEACHING SEQUENCES

SUMMARY The performance of a final hydrogen peroxide stage (P), applied instead of the conventional chlorine dioxide stage (D) in the ECF bleaching of E. globulus kraft pulps, has been studied. Two industrial DED and OQ(PO)D bleached pulps were further bleached in the laboratory either with a D or a P stage until 90 ± 0.5% ISO brightness. The papermaking potential of the four fully bleached pulps was assessed with respect to pulp beatability and strength/optical properties of the produced handsheets. The decomposition of peroxide in the final P stage of the DEDP and OQ(PO)DP sequences was estimated. While chlorine dioxide charge was nearly the same for both sequences, a much higher peroxide charge was needed in DEDP. The differences on bleachability with a final P stage were related to bleaching history impact on the nature and content of transition metals, residual chromophores as well as on additives performance. Decomposition reactions contribute significantly to peroxide consumption, especially at higher temperatures. Depending on the bleaching history, autoxidation reactions could contribute to the brightness gain at the final P stage. The papermaking properties revealed the advantages of final peroxide bleaching regarding pulp brightness stability, beatability, tensile strength, air resistance, bulk and opacity.