Bleaching of Eucalyptus grandis chemimechanical pulps

AREA, M.C.; BARBOZA O.M.; VALADE, J.L.

TAPPI JOURNAL

TECH ASSOC PULP PAPER IND INC

Año: 1997 vol. 80 p. 141 - 145

0734-1415

One-stage and two-stage bleaching trials were carried out to obtain high brightness levels in Eucalyptus grandis chemimechanical pulps of 49.5% (Elrepho) initial brightness. Peroxide bleaching was performed in standard conditions at five levels of two variables, hydrogen peroxide concentration and sodium hydroxide concentration. The maximum brightness found were 76.5 % in the one-stage trials and 78 % in the two-stage trials. Peroxide consumption in the one-stage process depended exclusively and linearly on the initial charge. Brightness reached a ceiling with higher charges of peroxide (approximately 78 % with 4% of initial H2O2. In the range studied, brightness and mechanical resistance increased linearly with the initial NaOH charge. In the two-stage process, brightness varied quadratically with the initial peroxide charge, indicating a maximum around the central point. Optimum conditions were found when an equal proportion of reagent loads was distributed in each stage.