Study of neem bark tannins for the leather industry

Neem bark (Azadirachta indica) contains a mixture of complex chemical components identified as: One procyanidin trimer: C1: Epicatechin- [4a-8] -epicatechin. Four Dimers: B1: epicatechin. Epicatechin- [4p-8]-catechin B2 Epicatechin- [4p-8]-epicatechin B3 Catechin-[4a-8]-catechin B4 Catechin-[4a-8]-epicatechin. Four well known monomers (+)-Catechin, (-)-Epicatechin, (+)-Gallocatechin, (-)-Epigallocatechin. Other compounds Quercetin, Kaempferol, Fisetin and Gallic acid. These compounds were characterised by chromatographic and spectroscopic techniques, including by thiolytic degradation with toluene-a-thiol and using acetylated and methyl derivatives. Structural elucidation of the cleavage products was by -NMR. The backbone of the isolated compounds consisted mainly of a mixture of flavan-3-ol units with 2R- configuration. The purity of monomers, dimers and trimer was checked by HPLC on Lichrosorb RP- 8 column. The molecular weight distribution ranges between 250 and 5500 and the average molecular weight distribution was found to be 1550 by gel permeation chromatography. Gas chromatography-mass spectroscopy demonstrated the complex nature of NBT molecular masses consist of monomelic, dimeric and trimeric units of procyanidin B and C types respectively. IR and FT-IR spectroscopy results were consistent with the rest of the techniques used. The hydrothermal stability of neem bark tannin tanned and crosslinked hide powder and leathers was found to be paralleled to mimosa tannin extract. Studies of the physical properties of tanned and retanned leathers showed comparability of neem bark tannins with mimosa tannin extract.