Effect of Pickling Materials on Leather Quality from a Hide Surface Charge Perspective

Abstract

Salt-free pickling technology has recently received increased attention because it produces much lower salt pollution than the conventional pickling technology using formic acid, sulfuric acid, and sodium chloride. However, the existing salt-free pickling materials, for instance, aromatic sulfonic acids (ASAs), lead to reduced leather quality and the reason behind this phenomenon is unclear. In this study, we explored how ASAs affect the properties of tannedleather. Results showed that typical ASAs, such as 5-sulfosalicylic acid, 1,5-naphthalenedisulfonic acid, and 2-naphthalenesulfonic acid, penetrated cattle hide more slowly compared with formic and sulfuric acids because of their large molecular weight and strong intermolecular interactions with hide collagen. ASAs decreased the positive charge of the pickled hide via interactions with their sulfonic acid groups, resulting in the increased adsorption rate of chrometanning agent to the hide surface. Rapid tanning agent adsorption could impede the deep penetration and uniform distribution of the agent in the ASA-pickled hide. Thus, the properties of wet blues and crust leathers pickled with ASAs are inferior to those of wet blue and crust leather pickled using conventional pickling materials. Our results indicate that a strongly positive charge of the pickled hide is vital to obtaining high-quality leather and provide insights into salt-free pickling materials from a hide surface charge perspective.