Functional pectin-based chromium-free tanning agent with outstanding antimicrobial and yellowing resistance toward sustainable leather processing

Abstract In recent years, chromium-free tanning agents have gained widespread attention as eco-friendly and non-toxic alternatives in the leather industry. However, most commercially available options still suffer from poor stability under wet and heat conditions, lack of antimicrobial properties, and susceptibility to yellowing. Herein, pectin (P) was oxidized by sodium periodate (NaIO 4 ), green ethylene glycol diglycidyl ether (EGDE) was then used for graft modification, resulting in the successful synthesis of a multifunctional, green oxidized pectin-EGDE (OPE) as a chromium-free tanning agent. Characterization by FTIR, XPS, XRD, and 1 H NMR indicates that OPE has an oxidation value of 68%, epoxide value of 0.34 mol/100 g. Leather tanned with OPE demonstrates remarkably improved properties compared to traditional chromium-free tanning agents (F-90 and TWS), including high thermal stability (shrinkage temperature of 80.5 °C), superior softness (6.3 mm), tensile strength (13.3 MPa), and tear strength (57.3 N/mm). Moreover, the leather tanned with OPE also exhibits significant antimicrobial properties (inhibition zone diameters of 15 mm against S. aureus and 18 mm against E. coli ), resistance to yellowing, and biocompatibility. Notably, the biodegradability of the wastewater from OPE tanned leather (BOD₅/COD ≥ 0.3) and its life cycle assessment confirm its unique environmental advantages. Overall, this work uses natural polysaccharides as the raw material to develop a green functional tanning agent, offering an innovative and sustainable solution for advancing the leather industry toward greener development. Graphical Abstract