Integrating laccase–mediator treatment into an industrial‐type sequence for totally chlorine‐free bleaching of eucalypt kraft pulp

Abstract

AbstractEnzymatic delignification using the high‐redox potential thermostable laccase from the fungus Pycnoporus cinnabarinus and a chemical mediator (1‐hydroxybenzotriazole) was investigated to improve totally chlorine‐free (TCF) bleaching of Eucalyptus globulus kraft pulps. Different points of incorporation of the enzyme treatment into an industrial‐type bleaching sequence (consisting of double oxygen, chelation and peroxide stages) were investigated in pressurized laboratory reactors. The best final pulp properties were obtained using an OOLQPoP sequence, where a laccase–mediator stage (L) was incorporated between double oxygen and chelation. The worse results, when the enzymatic and chelation treatments were combined in a unique stage, seemed related to partial inhibition of laccase‐mediator activity by the chelator. The new TCF sequence including the laccase stage permitted to improve eucalypt pulp delignification to values around kappa 5 (hexenuronic acid contribution over 50%) compared to kappa 7 using only TCF chemical reagents. In a similar way, the final brightness obtained, over 91% ISO, was 3–4 points higher than that obtained in the chemical sequences. Although technical and economic issues are to be solved, the results obtained show the feasibility of integrating a laccase–mediator treatment into a TCF sequence for bleaching eucalypt kraft pulp. Copyright © 2006 Society of Chemical Industry