Performance Evaluation and Sustainable Application of a Ternary Composite Non-Chromium Metal Tanning Agent for Breaking the Chrome Tanning Paradigm Wei Ding, Tengteng Zhang, Kanglei Wang and Haiteng Liu

Abstract

The environmental risks associated with chrome pollution in the leather industry are escalating. Developing easy-to-use chromium- free tanning technologies is imperative to ensure the sustainable development of the leather industry. Herein, a facile ternary composite non-chromium metal tanning agent (TCMT) was prepared by blending aluminum, zirconium, titanium salts, sodium citrate, and white zeolite powder. Then, the tanning performance of TCMT combined with an amphoteric phenol-based synthetic tannage (Shenotan JAN) was systematically evaluated through comparative analysis against a commercial zeolite tanning agent (ZLR-100). Results showed that the preferred tanning protocol involved initially treating the pickled sheep skin with JAN, followed by subsequent TCMT tanning in the same bath. The optimized dosages of JAN and TCMT were 2% and 8% based on twice the weight of pickled sheep skin, respectively. Under this condition, the tanned leather had a shrinkage temperature up to 83.4°C, along with a well-dispersed collagen fiber network, which was better than that of leather tanned by ZLR-100. Besides, the TCMT-JAN-tanned crust leather exerted much higher tensile (19.7 vs. 14.9 N/mm²) and tear strengths (49.3 vs. 41.3 N/mm) than ZLR-100-tanned crust leather, as well as comparable elongation at break (77.4% vs. 76.7%), softness (6.6 vs. 6.4 mm), fullness, and grain smoothness. Overall, this work provides innovative insights into developing user-friendly and facile chromium-free tanning agents, thereby contributing to the sustainable advancement of the leather industry through eco- efficient technological implementations.