The effect of wood supply and bleaching process on pulp brightness stability
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Universidade Federal de Viçosa
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One hundred different 5.5-year-old Eucalyptus grandis x Eucalyptus urophylla wood cloneswere cooked to kappa number 15-17.5 and the resulting kraft pulps oxygen-delignified to kappa 9.5-11.5under fixed conditions, except for chemical charges. Thirteen samples showing large variations in effectivealkali requirement, pulp yield and O-stage efficiency and selectivity were selected for brightness reversionstudies. These samples were bleached to 90-91% ISO by DEDD and DEDP sequences and their brightness stabilityand chemical characteristics determined. Heat reversion of the eucalyptus kraft pulps was strongly influencedby the wood supply, with brightness loss varying in the range of 2.1-3.6 and 0.8-1.7 %ISO for ODEDD andODEDP bleached pulps, respectively. Pulps bleached by the ODEDP sequence showed reversion values 1.3-1.9 % ISO lower than those bleached by the ODEDD sequence. Pulp carbonyl content decreased by 35-40%during the final peroxide bleaching stage. Carbonyl and carboxyl groups correlated positively with brightnessreversion, as did permanganate number and acid soluble lignin. Pulp final viscosity and metal and DCM extractivescontents showed no significant correlation with brightness reversion. Pulping, oxygen delignification andECF bleaching performances also showed no correlation with brightness reversion.
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