Preparation of Sulfonated Carbohydrazide-Glyoxal Based Retanning Agent and its Use in Manufacture of Sustainable Leather

Amino resins used in leather processing are produced from formaldehyde which is a carcinogenic species. Such resins may tend to release free formaldehyde in leather thus making it objectionable. The current study is designed to produce formaldehyde-free retanning agents by using carbohydrazide as an amino moiety and glyoxal as a condensing agent. Moreover, hydrophilic properties were achieved by sulfonating the resins with sulfamic acid. A series of resin samples were synthesised by reacting these products at varied mole ratios. The synthesised resins were tested for their viscosity measurements and also characterised by FTIR, TGA and SEM analysis. Sulfonated carbohydrazide based resins produced in this study were comparatively evaluated for their retanning properties in comparison with a commercial amino resin as a control. The results for retanning properties showed that there was a significant improvement in the mechanical and organoleptic properties of leather produced by the experimental resins as compared to the control. SEM analysis of the retanned pieces of leather reflected the improved cross-linking of collagen fibres and uniform filling of experimental resin in grain and fibre structure. FTIR studies for functional group analysis were carried out and TGA was run to evaluate the thermal stability of experimental resins. Estimation of free formaldehyde content in leather confirmed its 100% reduction for experimental resins whereas 143mg/kg formaldehyde was noted for the control resin. Free formaldehyde was also absent in effluents of the experimental resin whereas 273mg/kg formaldehyde was detected in effluent received from control resin. Moreover, percentage reduction of pollution load like COD, TDS and TSS of retanning effluent was observed as 12.60, 10.71 and 8.82 respectively for the experimental resin. The carbohydrazide based resin produced in this study was formaldehyde-free and useful in making green leather with improved retanning properties.