Valorization of Pomegranate Peel Waste as Retanning Agent in Leather Industry and Investigation of Its Effect on Prevention of Cr(VI) Formation

Abstract

Although Cr(VI) is not used in any step of the manufacturing process, the entity of Cr(VI) in leather and leather products has become a concern in the leather industry. Formation of free radicals may bring about conditions for the oxidation of free Cr(III) (if exists in leather) to Cr(VI) and these oxidations are usually catalyzed by heat and UV radiation. Antioxidants have an important role in order to inhibit oxidant compound activity by donating an electron to compounds. There are many studies on the prevention of Cr(VI) formation in leather production. The inhibiting properties of Cr(VI) formation were usually investigated by using commercial vegetable tannins (polyphenols) together with other retanning agents in retanning process. However, no study has been conducted on the possible use of pomegranate peel tannins as an alternative retanning agent, which is known as an important source of antioxidants, in leather making and their ability to prevent Cr(VI) formation. In the present study, pomegranate peels were extracted in different solvents and total phenolic content and antioxidant power of the extracts were determined by Folin-Ciocalteu, FRAP (The Ferric Reducing Ability of Plasma) and TEAC/ABTS (Trolox-Equivalent Antioxidant Capacity/2,2’-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid)) methods. Furthermore, different amounts of pomegranate peel extracts were used in retanning processes and the leathers were investigated in terms of increases in thickness, color changes as well as effect on prevention of Cr(VI) formation. The results revealed that besides noticeable retanning performance, pomegranate peel extract has a spectacular effect on prevention of Cr(VI) formation as compatible with its antioxidant power.