Challenges of Lab-Scale Study and the Influence of Wet-Finishing Agents in the Leather Dyeing Process

Abstract

The leather production process includes several interconnected steps. Dyeing is a critical step as it is responsible for the attractive visual appearance and quality properties that meet customer expectations. Obtaining homogeneous leather with effective dyeing is a challenge for tanneries, as leather is a complex and heterogeneous material. Effective dyeing depends on good execution of the process, raw materials and the performance of previous steps. To reduce costs and optimize processes, laboratory-scale tests precede industrial implementation. However, scaling-up from lab-scale to industrial scale production requires a deep understanding of critical variables that directly affect dyeing quality and efficiency. This work investigates factors that affect dyeing, aiming to understand the transition from the laboratory scale to the industrial scale. Bath exhaustion and dye penetration tests were used to evaluate the influence of the variables mass, retanning agent, dyeing auxiliary and type of agitation on leather dyeing. Results show that the influence of retanning, dyeing and fatliquoring agents on leather dyeing demonstrated that for small pieces of leather, the difference in thickness will affect more on the dye penetration than on the exhaustion of the bath due to the low mechanical action generated. While the exhaustion will be more affected by the products used. For leathers with different masses, the greater mass was more influenced by the products used, presenting a shorter penetration time when retanning, dyeing auxiliary and higher dye concentration were used, a behavior expected for leather. This improvement with the use of auxiliaries is associated with the mechanical action caused by the greater mass of the drum, which was not possible with the smaller mass.