Lignin-Derived Chrome-Free Tanning Agent toward Efficient and Sustainable Leather Processing

As one of the earliest natural materials utilized by humans, leather demonstrates superior water vapor permeability, mechanical strength, and wearability, occupying a pivotal position in daily life. Tanning represents a core process in leather manufacturing. However, traditional chrome tanning agents can form chromium-containing wastewater and sludge, blocking the leather industry’s path to sustainability. Herein, using a renewable natural biomass material (Sodium lignosulfonate, LS) and an eco-conscious epoxy monomer (Triglycidyl isocyanurate, TGIC), a green lignin-derived chrome-free tanning agent (LST) was synthesized via a facile one-pot grafting reaction. Characterization by FTIR, 1 H NMR, and gel permeation chromatography (GPC) verified the successful grafting of TGIC onto the LS molecular chain, and the resultant LST maintained abundant terminal epoxy groups (epoxy value = 0.139 mol/100 g). The application outcomes revealed that the shrinkage temperature ( T s ) of leather tanned with LST reached 83.6 °C, which is higher than that of commercially available chrome-free tanning agent F-90 (81.6 °C) and substantially surpasses that of TWS (76.3 °C). Additionally, LST-tanned leather demonstrated superior physical and mechanical properties, anti-yellowing performance, and filling efficiency. Collectively, these results uncover that LST, a novel environmentally friendly chromium-free tanning agent, holds broad application prospects in reducing chromium and salt pollution while enhancing the comprehensive performance of leather. This study provides a promising direction for sustainable leather processing and aligns with the circular economy strategy under the “dual-carbon” goals.