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The chrome tanning process is increasingly restricted due to severe health concerns and environmental hazards caused by chromium under certain environmental conditions. Heterocyclic derivatives evoke a huge array of interest as an alternative for the metal-free tanning process. Oxazolidine, one such saturated heterocyclic compound, is known for tanning; however, formaldehyde toxicity has been associated with it. In this current study, (3,5-dimethyl-1H,3H,5H-oxazolo­[3,4-c]­oxazol-7a­(7H)-yl) methanol and polyallylamine have been synthesized and their potential as chrome-free and formaldehyde-free tanning agents has been explored. The synthesized oxazolidine has been characterized by ultraviolet–visible spectroscopy, nuclear magnetic resonance spectroscopy, electronspray ionization–mass spectrometry, and attenuated total reflectance–Fourier transform infrared spectroscopy. Polyallylamine has been synthesized by solution polymerization and introduced alongside oxazolidine to create additional amine binding sites to improve the functional properties of the leather. 10% oxazolidine and 2% polyallylamine have been optimized to achieve 82 °C hydrothermal stability for leathers. The BOD/COD ratio of the oxazolidine tanning process is relatively less compared to the conventional chrome tanning process. The physical strength characteristics and organoleptic properties of the oxazolidine-tanned leather have been found to be better than those of the chrome-tanned leather. Thus, the current study paves way for an eco-friendly alternative to chrome- and metal-free tanning process as a greener and cleaner leather processing system.

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Organic tanning agents present a huge opportunity for developing tanning agents devoid of metals for sustainable and cleaner leather processing. An ideal tanning agent should be nontoxic, biocompatible, and cost-effective. Herein, we report an aromatic aldehyde-based modified vanillin synthesized by a singlestep substitution reaction that can be used in the tanning process. Also, multifunctional polymers with three groups (carboxyl, longchain hydrocarbon, and quaternary ammonium) are synthesized using hydroxyethyl methacrylate monomers, which can be used in the post-tanning process. The interaction of the modified vanillin derivative with collagen was studied at the molecular and fiber levels. Circular dichroism studies confirm no changes in the triplehelical conformation with increasing concentrations of modified vanillin. The crosslinking mechanism of collagen-modified vanillin by imine bond formation was confirmed through XPS. Further, the tanning input of modified vanillin was optimized, and 10% modified vanillin-tanned leather achieved 70 °C hydrothermal stability. For an integrated post-tanning process, the synthesized multifunctional polymer results in the increased uptake of dye and fatliquor. Further, the experimental leathers showed homogeneous pore size distribution, better fullness, and good mechanical strength. As expected, the pollution load of the experimental organic tanning process is significantly lesser than that of the chromium process. Thus, the present study overlays a greener metal-free leather-processing strategy.