① Destroy or modify the structure of chromophoric groups (delignification or alteration of lignin structure). ② Prevent or eliminate the combination between chromophoric groups and auxochromic groups. ③ Block the conjugation of chromophoric groups. ④ Inhibit the formation of new chromophoric groups.
① Sodium silicate: On one hand, sodium silicate buffers the pH value of H₂O₂ bleaching liquor; on the other hand, it inhibits the ineffective decomposition of H₂O₂. ② Oxygen: Introducing oxygen during H₂O₂ bleaching can strengthen the delignification process.
The basic principle of oxygen bleaching is to utilize the strong oxidizing property of molecular oxygen to oxidize and degrade lignin in pulp under alkaline medium, so as to dissolve out lignin.
During bleaching, H₂O₂ continuously releases HOO⁻ under alkaline action. HOO⁻ reacts with pigments continuously to achieve the bleaching effect.
H₂O₂ + NaOH → HOO⁻ + Na⁺ + H₂O The hydroperoxyl anion (OOH⁻) serves as the primary active bleaching component.
