Synergistic improvement of bleachability for poplar chemi-thermomechanical pulp in weakly-alkaline hydrogen peroxide...

The pulp and paper industry faces the challenges of fiber shortages and environmental concerns, with high-yield pulping emerging as one of significant solutions. However, high-yield pulp (HYP)'s high lignin content limits the brightness itself. While conventional alkaline hydrogen peroxide (H₂O₂) bleaching is effective, it causes the fiber yield loss and anionic trash, whereas weakly-alkaline H₂O₂ bleaching struggles with brightness. Enzymatic pre-treatment provides a precise fiber modification. However, most previous studies have been conducted either under strongly alkaline conditions or using single-enzyme systems such as xylanase. This work addresses this gap by proposing a synergistic enzyme pre-treatment strategy to improve the bleachability of poplar chemi-thermomechanical pulp (CTMP) in weakly-alkaline hydrogen peroxide bleaching. A systematic evaluation of enzymes revealed that the xylanase-pectinase combination exhibited remarkable synergistic effects, surpassing the performance of individual enzyme pre-treatments. Specifically, the brightness of bleached poplar CTMP reached 74.05 % ISO, compared to 70.72 % ISO of the untreated one, while maintaining a favorable bulk (2.40 cm³/g). This xylanase-pectinase pre-treatment effectively disrupted lignin-carbohydrate complex linkages, enabling deeper penetration of bleaching agents into the fiber cell wall, thereby enhancing pulp brightness. These findings offer a molecular-level understanding of how enzymatic synergy disrupts lignin-carbohydrate complex linkages and facilitates more effective bleaching.