Facile extraction and prospective application of indigenous Cassia fistula tannin in sustainable leather manufacture

Abstract

Vegetable tanning compounds have recently gathered attention as an environment-friendly, sustainable alternative to basic chromium sulfate in leather manufacturing. This study used different solvents such as water, methanol, and ethanol to extract tannins from Cassia fistula bark, a waste part of a tree. Ethanol proved the most effective solvent, yielding an extraction efficiency of 21.4 ± 0.61%. The bark extract was characterized with Fourier Transform Infrared Spectroscopy (FTIR), UV-Vis spectrophotometry, and Reverse Phase High Performance Liquid Chromatography (RP-HPLC). Gallic acid and rutin were discovered at high levels of tannins and polyphenolic compounds, including gallic acid (114.29 mg/100 g dry extract) and rutin (45.71 mg/100 g dry extract) whereas catechol and cinnamic were absent. The extracted bark exhibited a pH of 4.01 ± 0.04 and a moisture content of 4.89 ± 0.17%. Full vegetable, semi-chrome, and chrome re-tanned upper leathers were prepared using Cassia fistula bark extract to assess the tanning performance. Full vegetable leather displayed a reasonable shrinkage temperature of 85.77 ± 1.83 °C. All three types of upper leather met the United Nations Industrial Development Organization (UNIDO) standards of different parameters such as tensile, tear, and grain cracking strength, elongation, distention at grain crack, and flexing endurance. Field Emission Scanning Electron Microscope (FESEM) analysis revealed high fiber dispersion, indicating a higher cross-linking reaction within the leathers. Overall, the results suggested that Cassia fistula bark tannin may serve as a viable and renewable substitute for chrome tanning agents, providing a sustainable source of natural tanning material for leather manufacture.