Vegetable Tannins as Chrome-Free Leather Tanning

The purpose of this study is to replace chrome tannins with ecofriendly vegetable tannins as an alternative solution to prevent the public health and the environmental pollution. Vegetable tannin was extracted from Cassia singueana bark using an aqueous extraction method and applied on sheep pickle pelt. Optimum tannin extraction parameters were identified at powder concentration of 80 g/L, extraction temperature of 100°C, and extraction time of 120 mins. Chemical functionality of Cassia singueana extracted tannins was evaluated via FT-IR spectroscopy. Hence, the FT-IR spectrum confirmed the presence of wide band of phenolic hydroxyl (OH−) and carboxyl (C-O) groups connected with the aromatic ring. Moreover, physicochemical performance of the Cassia singueana extract tanned leather sample was scientifically examined and showed comparable results to conventional Mimosa tanned leather sample. The shrinkage temperature of Cassia singueana extract tanned leather recorded 83°C which is slightly higher than that of Mimosa extract (standard), 80°C. The results of mechanical properties such as tensile strength, tear strength, and elongation at break of Cassia singueana extract tanned leather sample are 15.6 N/mm2, 24.2 N/mm, and 45.3%, respectively, which are relatively higher than those of Mimosa extract tanned leather sample. A relatively higher reduction level of pollution load (BOD, COD, and TDS) was observed in the wastewater released from Cassia singueana bark extract compared to the Mimosa extract (standard). Finally, findings from this study revealed that Cassia singueana bark extract could be considered as an alternative source of vegetable tannins to reduce the consumption of chrome tanning in the leather tanning industry.