pH-Sensitive and Chromium-Loaded Mineralized Nanoparticles as a Tanning Agent for Cleaner Leather Production

Abstract

In this work, pH-sensitive and chromium-loaded mineralized nanoparticles (Cr-PPA NPs) were developed by self-assembly of poly (poly(ethylene glycol) methyl ether acrylate-co-acrylic acid) (poly(PEG-co-AA)) copolymers templated Cr(OH)3 mineralization. The Cr-PPA NPs exhibit excellent colloidal stability in water with high salt concentration, protein, and pH above 3.0. As a novel chrome tanning agent, such Cr-PPA NPs could effectively protect and deliver chromium into pickled pelt without reacting with collagen fibers during the penetration process, due to its antifouling PEG surface and nanosize. When the interior pH of the pickled pelt was lower than 2.5, the dissolution of the mineralized Cr(OH)3 core would cause disassembly of Cr-PPA NPs and rapid release of Cr3+ ions, leading to uniform chromium distribution in leather. After basifying, the released Cr3+ ions would cross-link the carboxyl groups both on collagen fibers and poly(PEG-co-AA) copolymers, resulting in chromium adsorption efficiency in leather higher than 90% and less chromium discharge in wastewater. Simultaneously, the resultant leather was given enhanced hydrothermal stability and physical properties based on above efficient chromium cross-linking. Compared with traditional chrome tanning agent, this pH-sensitive Cr-PPA NPs can really break through the existing balance limitation between chromium penetration and combination in the conventional tanning process and become a promising strategy for cleaner leather production.