Effect of Enzyme on Chromed Leather Dyeing With Acidic Dyes

Leather dyeing is a difficult task due to its heterogeneity and complexity. Several studies are aimed at improving the effectiveness of dyeing, including process optimization, use of dye auxiliaries, ultrasound, liposomes, and enzymes. Enzymes are receiving more attention due to their selectivity and high activity under optimum conditions. They are already applied in pretanning; however, information about enzyme application in the dyeing process is very limited. The study is aimed at investigating dyeing using enzyme preparation in the process together with a dye or pretreating leather with enzyme preparation prior to dyeing and comparing it with conventional leather dyeing. The results of the leather dyeing showed better adsorption in a control compared to the experiments, and it was also observed that the process is temperature dependent. Dyeing experimental samples had different kinetics. Using low dye concentration, enzyme preparations together with dye at 40°C resulted in the lowest adsorption; however, with higher dye concentrations, the tendencies were different. Fiber dyeing showed that pore removal has influence on enzymatic dyeing processes; dyeing together with EP resulted in better dye adsorption compared to EP pretreatment. To assess adsorption isotherms, three equations were applied: Langmuir, Freundlich, and Redlich–Peterson. The correlation coefficient showed that a suitable model depended on the sample and dyeing conditions. In some cases, the more suitable isotherm was Langmuir; in the other, it was Redlich–Peterson. The Langmuir adsorption capacity Q L depended on the sample, the control had the highest values, and it increased with increasing temperature. Freundlich’s constant n indicated that all three processes are favorable. Although control dyeing had a higher dye exhaustion, better diffusion was observed with enzyme preparation. EP dyeing not only led to better dye diffusion into leather but also resulted in a darker shade compared to pretreated samples. Research results give new insight into the mechanism of the enzymatic dyeing process and its effect on dye penetration and color index values between samples.