Bleaching of kraft pulp with commercial xylanases

The perform ance of commercial xylanases in totally chlorine-free bleaching of kraft pulp from conifer was tested with Pulpzyme HC (Novo Nordisk) and Cartazyme NS-10 (Sandoz/Clariant), at 500 U/kg of dry pulp, respectively. The treatment with Pulpzyme (X_p) or Cartazyme (X_c) has been combined with stages of bleaching using: oxygen (O), sulfuric acid (A), and extraction with 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 extreaction, and hypochlorination) was, used for comparison. The following average values were obtained: 1. Kappa number: OX_pAE_op, 4.8; OX_cAE_op, 4.9; XpOAE_op, 5.0; XcOAE_op, 4.9; OAE_op, 5.6, and CEH, 1.9; 2. Brightness (% ISO values): OX_pAE_op, 68.4; OX_cAE_op, 70.1; X_pOAE_op, 67.9; X_cOAE_op, 26.9; X_pOAE_op, 23.4; X_cOAE_op, 23.1; OAE_op, 25.4, and CEH, 25.2. Pulps that were treated with xylanases, before or affer the delignification with oxygen, have shown reduced kappa number and higher brightness than the pulp OAE_op, Enzyme treatment before delignification with oxygen reduces pulp viscosity. Brightness obtained for pulp produced with bleaching sequences containing the enzymatic treatment, when compared with the control, CEH, shows that the xylanases enhance the action of the bleaching agents.