A new strategy for biological enzyme bleaching: combined effects of laccase, xylanase, and mannanase in the bleaching of softwood kraft pulp – a synergistic effect of enzymes

Abstract Although highly efficient, conventional chemical bleaching is criticized for its high cost and environmental impact. In contrast, enzyme bleaching offers a sustainable and eco-friendly alternative, especially in elemental chlorine-free (ECF) and total chlorine-free (TCF) processes. This study investigates the synergy of laccase, xylanase, and mannanase in the ECF bleaching of softwood kraft pulp, focusing on their effects on fiber morphology and bleaching performance. The results demonstrate that laccase effectively oxidizes lignin, enhancing pulp brightness, while xylanase and mannanase improve bleaching efficiency by breaking down hemicellulose. The addition of mannanase during the enzymatic treatment increased the pulp brightness by 1.58 %ISO, with almost no negative impact on physical properties. The synergistic effect of the three enzymes increased the pulp brightness by 5.37 %ISO, reaching a maximum brightness of 92.35 %ISO. Furthermore, mannanase treatment significantly reduces the consumption of chemicals, cutting laccase and violuric acid usage by 38 % or decreasing total chlorine dioxide use by 13.26 %, while maintaining the same brightness level. These findings highlight the potential of using laccase, xylanase, and mannanase for efficient and eco-friendly pulp bleaching, contributing to resource conservation and environmental benefits. This study provides valuable insights into the industrial application of enzyme-based bleaching for sustainable paper production.