Treatment of Douglas‐Fir Heartwood Thermomechanical Pulp with Laccases: Effect of Treatment Conditions on Peroxide Bleaching

Abstract

Douglas‐fir heartwood thermomechanical pulp was treated with laccase enzymes at 25 and 50°C with and without added oxygen. The treated pulps were bleached with hydrogen peroxide at increasing alkali charges. Laccase treatments without added oxygen increased bleached brightness by 1.5–2.5 pts ISO, and decreased hydrogen peroxide consumption by 15–20%. The enzyme treatments were not enhanced when supplemented with oxygen. When the effectiveness of four different laccase enzymes was compared for the treatment of Douglas‐fir heartwood thermomechanical pulp, there were no significant differences found in the performance among the enzymes. Possible explanations for the observed results are given.

Keywords:

• Douglas‐fir
• thermomechanical pulp
• laccase
• hydrogen peroxide
• bleaching
• oxygen
• optimization
• quinones

We thank Science Council of British Columbia and NSERC for their financial support. We also thank Dr. Claus Felby and Dr. Lisa Viikari for donation of laccase enzymes for this work and the Pulp and Paper Research Institute of Canada for Preparation of Mechanical Pulps.