Implementing the "pulping black liquor utilization strategy for sustainable tanning": Establishment of waste...

Chromium pollution and the treatment challenges of pulping black liquor have severely restricted the development of the leather and pulp & paper industries. In the leather industry, the use of chromium-free tanning agents can avoid chromium pollution, but the current optimal substitute, the AlZr tanning agents, suffers from problems such as low tanning agent uptake rate, poor leather tanning performance, and low uptake rate of anionic wet-end materials due to the poor performance of ligands. In the pulp & paper industry, hemicellulose, as the second largest biomass resource in pulping black liquor, its high-value utilization can avoid resource waste and reduce the difficulty of black liquor treatment. Therefore, this study proposes a "pulping black liquor utilization strategy for sustainable tanning": Hemicellulose was extracted from pulping black liquor and oxidized with hydrogen peroxide to prepare a series of oxidized hemicellulose (OHC_(10-90)) with different oxidation degrees. After screening, OHC₇₀ (With aldehyde and carboxyl groups contents of 12.9% and 51.4%, and M_w = 1651 Da) demonstrated the optimal carboxylation effect on collagen fibers. Additionally, as a ligand, OHC₇₀ reacted with AlZr tanning agents to form novel complex tanning agent, which showed the best tanning effect. In the OHC₇₀-OHAZ₇₀ tanning system, the tanning agent uptake rate reached 98.3%, the shrinkage temperature of the tanned leather reached 96.8 °C and stable wash performance. Leathers' physical-mechanical properties, sensory characteristics, and uptake capacities for anionic fatliquors and dyes far exceeded those of leathers tanned with traditional AlZr agents and were comparable to those of Cr tanned leather.