Oxidative enzymes for fibre modification

The modification of chemical and mechanical pulp fibres was studied by using laccase produced by Trametes hirsuta. The modifications obtained were found to depend on the substrate primarily oxidized by the enzyme; e.g. the type of fibres and the mediators used. The oxidation of the substrate was directly followed by measuring the oxygen consumption and the results evaluated by testing the technical properties of the modified fibres. The reactivities of chemical and mechanical pulps were found to depend on the amount, but apparently also on the location and type of lignin present in the fibres. A synergistic effect in the oxygen consumption of fibre substrates was observed, when the mediator was added. Thus, the oxygen consumption in the mediated oxidation was higher than the sum of the oxygen consumption in the fibre or mediator oxidation alone. In the mediated oxidation of chemical fibres, delignification was obtained by using either the well known mediator HBT or a biological mediator; siderophore. Without an added mediator, the laccase treatment polymerized lignins of lower molecular weight which, in the case of mechanical fibres, resulted in improved strength properties. Thus, by optimizing the reaction conditions, with or without a mediator for different fibre substrates, beneficial modification of fibre properties could be obtained.