Efficient deep degradation of pulp lignin via a synergistic oxygen and high- proportion chlorine dioxide strategy

Bamboo is a fast-growing, high-biomass, and mechanically strong renewable resource. It shows great potential in cellulose-based materials and bio-based products. However, its complex tissue structure and unique lignin distribution limit the efficiency and applicability of conventional delignification processes. In this study, a synergistic lignin removal strategy combining high-proportion chlorine dioxide (ClO 2 ) pretreatment with oxygen delignification was developed. Two process sequences, O-D PI and D PI -O, were systematically compared in terms of reaction mechanisms during bamboo fiber lignin removal. Results showed that, in the D PI -O process, ClO 2 preferentially oxidized lignin to form quinone-type intermediates. These intermediates were then effectively degraded in the subsequent oxygen delignification stage. This led to a significantly higher lignin removal rate (84.90 %) and a notable reduction in kappa number (2.49) and AOX generation (0.267 kg/t pulp). Multidimensional characterization using 2D HSQC NMR and 31 P NMR confirmed more complete cleavage of S/G units and β-O-4 linkages in the D PI -O system. The carboxyl group content of residual lignin increased significantly to 1.194 mmol/g, revealing the critical role of quinone intermediates in deep oxidative degradation. Kinetic studies further showed that the lignin removal rate was highly sensitive to alkali concentration (a 1 = 0.6012), especially under low oxygen pressure. In low-alkali environments, oxygen pressure became more influential (b 1 = 0.1382). This study elucidates the reaction pathway and key controlling parameters of oxygen-assisted, high-proportion ClO 2 delignification. It provides both theoretical and practical support for efficient lignin degradation and high-purity cellulose fiber production.