Abstract

The mechanism of the combination tannage of a rare earth (Ce) bound with tannic acid is described in the paper. Based on the potentiometric titration in aqueous solution of Ce, Gallic acid (Ga) and Glycyl Glycine (GG), we found that that the formation constant of the complex CeGa increased with increasing temp, from 9°C to 30°C, lgkCeGa rose from 11.55 to 11.92, while the formation constant of complex CeGG decreased with increasing temperature, from 6.35 to 3.08.

Complex CeGa and mixed ligand complexes CeGaGG in the solid state display a stronger resistance to thermal decomposition than uncombined CeCl3, Ga and GG. When reacting Ce(III) and tannic acid with hide powder or modified hide powder either together or separately, it was found that Ce coordinated on tannins, while tannic acid combined with collagen, and this manner of combination played a important role in the combination tannage. Based on these studies, the paper proposed the concept “Poly–Strut Firm Structure” to explain the synergistic effect in rare earth-vegetable tannins combination tannage.