Hydro-brightening pretreatment removes antioxidant lumen extractives to enhance CMP bleachability

The poor bleachability of eucalyptus chemi-mechanical pulp (CMP) is widely recognized as a major challenge in the industry. In order to overcome these challenges, a novel and eco-friendly Hydro-Brightening Pretreatment (HBP) strategy is proposed, with the objective of enhancing the brightness of eucalyptus through the removal of bioactive lumen extractives (LEs) using hot water. The majority compositions of LEs are characterised as ellagic acid, taxifolin and caffeic acid. The disruption of chromophore formation is evidenced by the removal of these LEs. During the bleaching reaction, ellagic acid is converted into quinonoid rings via elimination reactions, and taxifolin is oxidised to form trihydroxy benzoic acid and dicarboxylic acids, while caffeic acid undergoes esterification. In comparison with the LEs retained strategy, the implementation of HBP resulted in an enhancement of the brightness of 2.53% ISO for Eucalyptus grandis CMP, and reached a brightness of 80.85% ISO for Acacia crassicarpa Benth. CMP. Concurrently, the LEs of Eucalyptus grandis manifest notable antioxidative capacity (IC 50 =36.13 for DPPH radical). Consequently, this work provides a strategy that simultaneously enhances CMP bleachability and explores the possibility of extracting high-value antioxidant products from LEs, offering new insights on improving CMP bleachability and potential added-value co-products. • A novel HBP strategy boosts pulp brightness by suppressing key chromophores formation. • This method achieves over 80%ISO pulp brightness, and yields valuable antioxidants. • This strategy is effective for enhancing bleachability across major pulping hardwoods.