Enzymatic delignification of kraft pulp using laccase and a mediator

Kraft and sulfite pulps were delignified using laccase and a mediator, ABTS [2,2'-azinobis-(3-ethylbenzthiazoline-6-sulfonate)]. Pulps were treated at 10% consistency under conditions (time, temperature, and pressure) compatible with industrial bleaching processes. Typical reaction conditions were 2 h at 60 degrees C, pH 5, O-2 pressure 300 kPa, 1% ABTS on pulp, and laccase at 5 U/g pulp. After one-stage treatment followed by alkaline extraction, the extent of delignification was 25-40% for kraft pulps and over 50% for a sulfite pulp. Repeating the treatment reduced the kappa number of a softwood kraft pulp by 55%. Pulp viscosity and strength following sequential enzyme treatment and alkaline extraction were comparable with those following alkaline extraction alone.