Vegetable tannin composition and its association with the leather tanning effect

The increasing environmentally friendly approach of using renewable materials has led to vegetable tannins having an important role as tanning agents in the leather industry. Tannins are complex phenolic structures, and the literature shows that a considerable amount of chemical parameters measured through analytical techniques can be associated with their tanning ability. In the present study, five types of vegetable tannins highly used in the tanning industry were chosen for the evaluation of some of their relevant chemical parameters and the correlation with their cross-sectional penetration in the hide. Black wattle (Acacia mearnsii), quebracho (Schinopsis lorentzii), chestnut (Castanea sativa), tara (Caesalpinia spinosa), and myrobalan (Terminalia chebula) were tested. The chemical properties of the total tannin polyphenols, non-tannin polyphenols, insoluble solids, soluble solids, total solids, total phenols, non-tannin polyphenols:total phenols ratio, and residual tanning float concentration were measured and associated with the leather cross-sectional penetration results. The statistical Mann–Whitney-U test showed that the insoluble solids, non-tannin polyphenols, soluble solids, and total tannin polyphenol percentages distinguished the groups of tannins that crossed the hide from those that did not well. Hence, since the analysis of insoluble solids is the simplest and the most direct among them, it would be recommended to use this parameter to define a cutoff to distinguish the performance of tannins for leather application.