Bleaching of kraft pulp with commercial xylanases

The performance of commercial xylanases in totally chlorine-free bleaching of kraft pulp from conifer was tested with Pulpzyme HC (Novo Nordisk) and C artazyme NS-10 (Sandoz/Clariant), at 500 U/kg of dry pulp, respectively. Th e treatment with Pulpzyme (X-P) or Cartazyme (X-C) has been combined with s tages of bleaching using: oxygen (O), sulfuric acid (A), and extraction wit h hydrogen peroxide (E-OP). The following sequences have been tested: OXpAE (OP'), OXcAE(OP'), XpOAE(OP'), XcOAE(OP') and OAE(OP). Kraft pulp bleached at the Klabin industrial plant using the sequence, CEH (chlorine, alkaline extraction, and hypochlorination) was used for comparison The following ave rage values were obtained: 1. Kappa number: OX(P)AE(OP') 4.8; OX(C)AE(OP') 4.9; XpOAE(OP), 5.0; XcOAE(OP), 4.9; OAE(OP), 5.6, and CEH, 1.9; 2. Brightn ess (% ISO values): OX(P)AE(OP'), 68.4; OX(C)AE(OP'), 70.1; X(P)OAE I 67.9; X(C)OAE(OP') 68.8; OAE(OP') 63.8, and CEH, 63.6; and 3. Viscosity (cP):OX( P)AE(OP') 27.6;OX(C)AE(OP') 26.9; X(P)OAE(OP') 23.4; X(C)OAE 23.1; OAE(OP') 25.4, and CEH, 25.2. Pulps that were treated with xylanases, before ore or after the delignification with oxygen, have shown reduced kappa number and higher brightness than the pulp OAE(OP). Enzyme treatment before delignifi cation with oxygen reduces pulp viscosity. Brightness obtained for pulp pro duced with bleaching sequences containing the enzymatic treatment, when com pared with the control, CEH, shows that the xylanases enhance the action of the bleaching agents.