A “wrench-like” green amphoteric organic chrome-free tanning agent provides long-term and effective antibacterial protection for leather

Organic chrome-free tanning agents are an important part of the sustainable development in leather manufacturing industry. However, organic chrome-free tanning agents tanned leather have a low isoelectric point (pI < 5), which results in a low absorptivity of traditional anionic wet finishing materials; as a result, leather quality is poor, and tannery wastewater is difficult to treat. In addition, leather is easily eroded by bacteria and mold during its production, storage, and use, causing serious economic loss to enterprises and users. In this study, hexahydro-1,3,5-tris(hydroxyethyl)-s-triazine (HHTT), ethylene glycol glycidyl ether (EGDE), and collagen polypeptide (CP) were used as raw materials to prepare a wrench-like, antimicrobial, amphoteric, epoxy-terminated, organic chrome-free tanning agent (HHTT-EGDE-CP) with a pI of 5.21, and an epoxy value of 0.267 mol/100 g. HHTT-EHDE-CP can establish a stable covalent cross-linking with collagen fibers, thereby enhancing the physicochemical properties of leather, the absorptivity of anionic wet finishing materials, giving leather long-term and efficient antibacterial properties. Experimental results show, that the shrinkage temperature (78.8 °C) and the absorptivity of anionic fatliquors (93.1%) and dyes (97.5%) of HHTT-EGDE-CP-tanned leather surpassed those of leather tanned using commercial organic chrome-free tanning agents. Notably, the inhibition rates of HHTT-EGDE-CP-tanned leather against E. coli and S. aureus reached 99.93% and 99.99%, respectively. In addition, HHTT-EGDE-CP-tanned leather exhibited excellent inhibition against A. flavus and Asp. niger, with long-term and efficient antibacterial properties. This innovative technique offers new perspectives for designing and developing multifunctional green materials toward the sustainable development of industrial manufacturing.