Determination of dye uptake in leather coatings for waterless leather dyeing by ScCO2 impregnation

During leather finishing the surface of leather is coated with coloured binder systems. In conventional finishing, two to five grams of dyestuff are used per square foot of leather. Due to so-called overspray, 40-60 % of dyestuff is lost. To increase resource efficiency, we examine the impregnation of dyestuff-free leather coatings using supercritical CO2 at 100 bar and 40 °C as a solvent for Solvent Red 111. The focus of the investigation is the effect of the layer thickness on the colour intensity. Furthermore, the dyestuff absorption capacity of the binder layer is determined. As result, a layer thickness of 23 µm allows the maximum achievable colour intensity. The dyestuff absorption capacity at this thickness is 35 mg of dyestuff per square foot of leather. This results in a saving potential for dyestuff of over 95 %.