ASSESSMENT OF VARIOUS COMMERCIAL ENZYMES IN THE BLEACHING OF RADIATA PINE KRAFT PULPS

Four xylanase preparations that are commercially available, namely Car tazyme from Sandoz, Ecopulp from Alko-ICI, Irgazyme from Ciba-Genencor and Pulpzyme HB from Novo Nordisk, were tested in bleaching experimen ts of kraft pulps from Pinus radiata. The main objective of this study was to optimize a reduction in the consumption of chlorine dioxide in the bleaching sequences C-90/D(10)E(o)DED, C-70/D(30)E(o)DED and D(10 0)EDED. Enzymatic treatments led to savings of ClO2 between 3.5 and 3. 9 kg per air-dried tons (ADT) in the three bleaching sequences, withou t affecting the target brightness of the pulps. In these assays, some minor although reproducible differences in the performance of the enzy mes were observed. In most cases, xylanase treatment partially affecte d the beatability of the pulps, measured as the number of revolutions in the PFI mill required to reach the same tensile index as the respec tive controls.