Bleachability of Eucalypt Kraft Pulp Derived from Auto-Hydrolyzed Chips, 2011 International Pulp Bleaching Conference
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Optimum conditions for eucalypt chip auto-hydrolysis and further kraft pulping and ECF bleaching were established. The chip auto-hydrolysis (30 min, 170oC) treatment decreased subsequent kraft pulping yield (44.9%) in relation to the reference (50.9%). At constant conditions, the oxygen delignification efficiency was 75% for the pulp from the 30-min auto-hydrolyzed chips and only 43.3% for the reference one, resulting in a 24% lower bleaching chemical cost for the former. However, at constant kappa drop (~42%) across O-stage, the relative bleaching chemical cost was about 22% higher for the pulp from 30-min auto-hydrolyzed chips. Bleaching yield values of the pulps from pre-treated chips were quite adequate but their final viscosities were much lower than that of the reference pulp at fixed oxygen delignification conditions; viscosities were improved significantly with proper optimization of the O-stage. The auto-hydrolysis treatment of the chips produced bleached pulp with lower coarseness, higher fiber and fines count and also negatively affected beatability and the mechanical and optical properties of the pulp, compared to the reference. Optimization of the oxygen delignification stage to a fixed kappa drop across the O-stage improved strength properties and beatability only slightly.