Recent advances in pitch control using the laccase-mediator system

Abstract

Lipophilic extractives from wood and nonwood fibers exert a negative impact in pulp and paper manufacture causing pitch deposits. We have shown the effectiveness of the laccase-mediator system in removing pulp lipids regardless the pulping process and the raw material used. The enzymatic treatments were performed using a fungal laccase from Pycnoporus cinnabarinus and 1-hydroxybenzotriazole (HBT) as mediator. Gas chromatography-mass spectrometry of extracts from the enzymatically-treated pulps revealed that most of the lipids (including free and conjugated sitosterol, fatty and resin acids, and triglycerides) were removed. Improved pulp brightness and decreased kappa number were also observed. Then, the chemistry of the reactions of lipophilic extractives with laccase-HBT was studied using model alkanes, fatty alcohols, fatty acids, resin acids, free sterols, sterol esters and triglycerides. The laccase alone modified some unsaturated lipids, however, the most rapid and extensive removal was obtained in the presence of mediator. Different degradation patterns were observed, and several oxidation products were identified. Lignin related phenols were tested as alternative to synthetic mediators for lipid removal from eucalypt pulp. Over 90% removal of free and conjugated sitosterol, similar to that attained with HBT, was obtained with some of them. A positive effect on pulp brightness and kappa number was also obtained, especially after a peroxide stage.