Sunt Bark (Acacia nilotica) Powder Combination Tanning for Manufacture of Upper Leather

Abdella M.H, Musa A.E, Ali S.B

When certain polyphenols and polycarboxyl group compounds are combined with metallic salts (not including chromium) a combination tanned leather is produced with good resistance to hydrothermal shrinkage and a “chemical effect” near to chrome tanned leather. The combination of vegetable tannins with metal salts has been used for thousands of years. The shrinkage temperature of semi-metal tanned leather is much higher than expected. This is an example of synergy, when the total effect is greater than the sum of the parts. In this study, combination tanning process based on Sunt (garad) bark – Aluminum tannage for the production of upper leathers is presented.  The bark powder of Acacia nilotica  (Sunt bark) from Sudan has been utilized in the combination tanning system with aluminum. Both tanning methodologies Sunt bark followed by Aluminum (Sunt bark -Al) and Aluminum followed by Sunt bark (Al- Sunt bark) have been attempted. All combinations tanning systems resulted in leathers with shrinkage temperature above 90oC. However, Al- Sunt bark leathers tanned using 2% Al2O3; followed by 20% Sunt bark resulted in shrinkage temperature of 96oC. It is seen that combination tanning using Sunt bark (20%) followed by Aluminum (2% Al2O3) resulted in leathers with shrinkage temperature of 100oC, which is 16oC more than the control (Sunt bark tanned) leathers.  The spent tan liquor analysis shows significant reduction in COD and TDS loads compared to a conventional vegetable tannage. Sunt bark -Al combination system resulted in leathers with good organoleptic and strength properties. The work presented in this paper established the use of Sunt bark - aluminum combination tanning system as a suitable alternative for chrome-free tanning system.