A Chitosan‐Modified Zeolite Chrome‐Free Tanning Agent: Interfacial Cross‐Linking Mechanism for Enhanced Collagen Stability

The development of chrome‐free tanning agents requires a fundamental understanding of the interfacial interactions between tanning agent particles and collagen matrices. Herein, the interfacial cross‐linking between collagen fibers and zeolite‐based tanning agents is investigated, focusing on the synergistic role of chitosan in modulating interfacial bonding. Acetic acid‐modified zeolite (HAc‐ZA) and chitosan‐synergistically modified zeolite (CSHAc‐ZA) were synthesized. Tanning trials show that CSHAc‐ZA exhibits improved dispersion within collagen. Solid‐state NMR and ATR‐FTIR reveal that Al species from zeolite convert from four‐coordinate to six‐coordinate upon interacting with collagen's carboxyl and amino groups, forming stable complexes. Small‐angle x‐ray scattering and DSC indicate enhanced thermal stability via an entropic suppression mechanism, reducing denaturation enthalpy while preserving fibrillar order. Zeta potential confirms the anionic character of zeolite‐tanned leather. CSHAc‐ZA‐tanned leather achieves a tensile strength of 20.4 MPa, a tear strength of 40.9 N/mm, and a dye uptake of 99.59%, surpassing commercial zeolite and conventional chromium agents. Wastewater analysis reveals significantly reduced COD and improved BOD/COD ratio. This work elucidates a synergistic “anionic coordination + hydrogen bonding + entropic suppression” mechanism at the zeolite–collagen interface, providing a theoretical foundation for eco‐friendly chrome‐free tanning agents.