The use of vegetable tanning materials in leather processing has drawn attention as an alternative to basic chromium sulphate for its natural abundance and environmental aspects. In this work, an attempt has been made to extract vegetable tannins from Xylocarpus granatum bark using different solvents (e.g., water, methanol, ethanol, and chloroform) and compare with conventional vegetable tanning agents such as mimosa and quebracho. The highest extraction efficiency was observed 31.22% by methanol. The presence of tannin content and polyphenolic compounds, e.g. (-)epicatechin (503 mg/100 g dry extract), catechin hydrate (218 mg/100 g dry extract), catechol (29 mg/100 g dry extract) were ensured by UV–Vis, FT-IR spectroscopy and HPLC. Again, condensed tannins, moisture content, and pH of the methanol extracted tannin were found 47.80%, 5.82%, and 3.97 respectively. The leather tanned by Xylocarpus granatum tannin showed a shrinkage temperature of 86.34 ± 1.52 °C. Other properties such as tensile strength, tear strength, grain cracking load, and distention at grain cracking were comparable to conventional vegetable-tanned leather. The cross-sectional morphology of the tanned leathers was also characterized by scanning electron microscopy (SEM) which revealed a compact structure of the leather fibers. In light of the findings from the study, X. granatum bark tannin could be a well alternative to chromium and a new source of vegetable tannin for the leather industry. Graphical Abstract

Environmental issues are nowadays the prime concern worldwide for leather industries due to chrome containing solid and liquid wastes generated from the tannery. Therefore, experts are being encouraged in exploring alternative tanning agents. This study aimed at applying a novel vegetable tanning agent extracted from Xylocarpus granatum barks for the production of semi-chrome (SC) and chrome retanned (CR) leathers to reduce chromium use. Characterization of the SC and CR leathers was performed by Fourier Transform Infrared (FTIR) spectroscopy which revealed prominent tanning activity of the extracted tannins. The tanned leathers exhibited shrinkage temperatures of 112˚C for SC and 103˚C for CR leathers. The physicomechanical properties were found as tensile strength >230 kg/cm2, tear strength >30 kg/cm, grain cracking load >20 kg, distention at grain crack >7 mm, ball bursting load >38 kg, and distention at ball bursting >12mm that was comparatively acceptable according to UNIDO standard for shoe upper leathers.