New possibilities of kraft pulp biobleaching with laccase and sulfonated mediators

Several phenolic sulfonated compounds, such as 1-phenol-4-sulfonic acid (PS), 1-naphtol-3-6-disulfonic salt hydrate (NDS) and 1-nitroso-2-naphtol-3,6-disulfonic acid (NNDS), were tested as laccase mediators in the biobleaching of eucalyptus kraft pulp. Laccase mediator systems oxidise the pulp lignin allowing its removal in subsequent alkaline extraction, but phenolic mediators can also couple to lignin by oxidative polymerisation reactions. Laccase NNDS system allowed a high delignification after alkaline extraction but also a significant coupling was produced. This coupling effect was employed for delignification by a subsequent acid treatment, suggesting the enzymatic formation of acid soluble lignin. A kappa number lower than 4 was obtained after a very simple totally chlorine free (TCF) biobleaching sequence based on this new approach. Both oxidation and coupling reactions could be used to perform pulp biobleaching: oxidised pulp could be alkaline solubilised, whereas the coupling reactions could help on solubilisation of lignin in different from alkaline mediums. (C) 2010 Elsevier Ltd. All rights reserved.