Coloration and Structural Characterization of Chrome Leather Using a Sulfonic Acid Group-Containing Imine-Based Azo Dye Polymer

The aim of this study is to investigate the applicability and performance of an imine-structured polymer-based dye in the coloration of chrome leather. For this aim, chrome-crust leather samples which were obtained from cattle hides were subjected to the standard stages of leather processing, namely back-wetting, neutralization, and dyeing. Dyeing was carried out using a solution containing 2% polymer dye and 1% formic acid (HCOOH) at pH 3.5, at 35 °C for 120 minutes. The dyed samples were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD) to evaluate their morphological and structural properties. SEM analysis showed that the dye was homogeneously distributed on the leather surface, resulting in a uniform coating. XRD analysis revealed the interaction sites of the dye with the skin matrix, the bonding regions, and the coating thickness. These results indicate that the imine-structured polymer dye not only forms a surface coating but also penetrates deeply into the skin matrix, creating a strong and permanent bond. They also show that the imine-structured polymer-based dye exhibits high efficiency in chrome leather dyeing, ensures homogeneous coloration, and is suitable for shoe upper leather production in terms of section-dyeing performance. These findings suggest that the polymer dye can be considered an innovative alternative for industrial leather dyeing.