Biobleaching of eucalypt kraft pulp with a two laccase-mediator stages sequence

A new biobleaching sequence, with two enzymatic stages based on the application of laccase-mediator systems, was tested (L1EL2QPo) in order to increase the effectiveness of enzyme delignification on eucalypt kraft pulp. Different synthetic – 1-hydroxybenzotriazole (HBT) and violuric acid (VA) – and natural – syringaldehyde (SyAl) – mediators were used in the laccase stages and the biobleached pulp were compared in terms of chemical, optical and physico-mechanical properties. The pulp bleached with HBT or VA showed similar delignification (64.1% and 65.9% respectively) and optical properties (86.4% and 86.1% ISO brightness respectively) than an industrial TCF pulp (68.3% delignification and 84.8% ISO brightness). SyAl improved these properties in a lower extent (56.71% delignification and 80.52% ISO brightness). Regarding physico-mechanical properties of pulp, the biobleaching sequence had no a negative effect, even some slight improvements were observed in very specific cases.