Facile synthesis of a new eco-friendly epoxy-modified oligomeric chitosan-based chrome-free tanning agent towards sustainable processing of functional leather

To reduce the contamination of Cr6+ and dyes from tannery wastewater, a chromium-free tanning agent with rich terminal epoxy groups (COS-GTE) was synthesized using oligomeric chitosan (COS) and glycerol triglycidyl ether (GTE). The structural characteristics and application performance of prepared COS-GTE were investigated by FTIR NMR, GPC, SEM, adsorption properties of fatliquor and dyes, and other analysis techniques. The application results indicated that the shrinkage temperature of finished leather tanned with COS-GTE can reach 83.5 degrees C. Compared with traditional tanning materials (F-90 and TWS), the finished leather had better mechanical properties (tear strength of 47.410 N/mm2) and yellowing resistance. Moreover, the natural skin modified with COS-GTE showed excellent antimicrobial properties against Escherichia coli, Staphylococcus aureus, Aspergillus flavus, and Aspergillus niger. Especially, the finished COS-GTE tanned leather had a high absorption rate of fatliquor (69.27 %) and dyes (X = 93.21 %), which is beneficial for reducing comprehensive wastewater pollution. The research revealed that the COS-GTE not only can be considered a new biomass material to solve the problem of chromium and dye contamination in the leather industry but also endows leathers with a unique antimicrobial function to extend product protection and service time.