Oxidized sodium lignosulfonate: A biobased chrome-free tanning agent for sustainable eco-leather manufacture

Chrome-free eco-leather manufacture is inevitable in sustainable development of the leather industry. Herein, oxidized sodium lignosulfonate (OSL) was prepared using H2O2 and CuSO4 catalyst as a biomass-derived tanning agent. H2O2 oxidation of OSL breaks the aliphatic side-chain β-O-4′, β-5′, and β-β' linkages, transforms the adjacent phenolic hydroxyl group and methoxy group on the benzene ring into carboxyl groups and reduces the colority. OSL120 (120% H2O2, Mw 1498) containing moderate carboxyl (6.27 mmol/g) and phenolic hydroxyl (0.18 mmo/g) appropriately coordinates with aluminum–zirconium salts (AZ), thereby promoting the uniform penetration of OSL–AZ complexes into the leather matrix. Moreover, OSL120 provides essential hydrophobic and hydrogen bonds interactions with collagen to form a rigid multi-point crosslinking network among collagen fibers. Thus, chrome-free tanned leather shows natural flesh color and shrinkage temperature up to 89.5 ℃, and crust leather with satisfactory physical properties are achieved. This work gives new insights into the low-carbon leather manufacture with lignin-based tanning system and provides a novel approach for the resource utilization of sodium lignosulfonate.