Characterization and application of Acacia nilotica L. as an alternative vegetable tanning agent for leather processing

Tanning is a very important process in the leather industry as it brings out the required characteristics in the raw materials, which are essential for the quality of the finished product. However, intense pressure from local and international environmental regulations for the reduction or elimination of chrome-containing solid waste from tannery effluent, has forced the leather industry to search for alternative tanning agents. Although there is no satisfactory replacement for chromium salt as yet, the tendency is still towards chromium-free production, ideally from renewable plant sources, and the production of metal-free leathers. In this study, tannins of Acacia nilotica L. were extracted with distilled water from the fruit of Acacia nilotica L., composed of pods and seeds, using a Koch extractor at 75°C for 8h. The molecular weight of the spray-dried tannins was measured by gel permeation chromatography (GPC), and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) characterized by fourier transform infrared spectroscopy techniques (FTIR-ATR). Tannins isolated from the Acacia nilotica L. fruit were quantitatively analyzed and a qualitative analysis of the acacia-tanned leathers was carried out with regard to shrinkage temperature, tensile strength, elongation at break, tear strength, and grain crack. A color measurement of the tanned leather was also carried out. Tanning with 20% Acacia nilotica L. tannin, based on skin weight, provided the optimum physical-mechanical and hydrothermal stability properties. Tanning with extract of Acacia nilotica L. resulted in relatively light-colored leathers with acceptable properties, comparable to commonly-used vegetable tannins. These results demonstrate the potential feasibility of using renewable plants for tanning purposes and tannin extract of Acacia nilotica L. fruit as a viable vegetable tanning material for the production of chromium-free leathers from sustainable resources.