Chromium Footprint Reduction: Nanocomposites as Efficient Pretanning Agents for Cowhide Shoe Upper Leather

We report a green chemistry approach to synthesized nanocomposites as pretanning agents in the cowhide shoe upper leather tanning process. Nano ZnO, as-prepared polymer, and polymer/ZnO nanocomposites as pretanning agents were respectively taken for the controls. The amount of chrome tanning agents reduced from 6% (conventional process) to 4% was added in the tanning process as a control process. Chromium footprints in wastewater and chromium distribution in leather samples were mainly analyzed. The results showed that the chromium footprint in the shoe upper leather marking was minimized when using nanocomposites compared with the control process, and the chromium content in leather increased from 13480 to 15039 mg·kg–1. Additionally, thermal properties, mechanical properties, softness, and dyeing fastness of the leather pretreated with nanocomposites were close to those of leather treated with the conventional tanning process. Scanning electron microscopy analysis indicated that leather pretreated with nanocomposites can be endowed with expected grain smoothness, good softness, and separated fibers. Nanocomposites applied as pretanning agents can effectively enhance chromium uptake in bath and fix firmly in leather, which will reduce emissions of chromium footprint in leather making.