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, 1H 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 (Ts) 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.