Abstract

The interaction of leather, prepared by the lime-free method, and a series of 1:2 metal complex dyes has been investigated by determining the distribution of the dyes at equilibrium. Kinetic and thermodynamic aspects such as the rate of dyeing, heat of dyeing, entropy, affinity of dyes on the lime-free and conventional leather have been studied. The diffusion coefficient was calculated by means of the Weisz pore and Krenk models.

It has been established that the sorption isotherms for these dyes on both types of leather fibres show a Langmuir type of behaviour. The dyeing system hydrophobic C.I. Acid Red 247/lime-free leather has a positive heat of dyeing: dyeing is an endothermic process in this case.

The change of entropy of interaction of hydrophobic C.I. Acid Red 247 and leather fibres is 24 cal/mol•K. An increased degree of freedom should be associated with water molecules such as those hydrating the dye and the fibre, and possibly, due to randomness in the fibre itself. This decreased degree of the order of water molecules results in a positive change of entropy, which then is the thermodynamic cause of the hydrophobic bonding.

The influence of factors such as, initial amount of dye, pH of leather and temperature on the dyeing process was established. The results have shown that lime-free leather absorbs lesser amounts of dye during dyeing but that, the dye penetrates more deeply compared with conventional leather. The amount of dye, pH and temperature has no influence on such a tendency.

On the other hand, the investigation has shown that the factors mentioned have a more marked influence on the progress of dyeing of lime-free leather compared with dyeing conventional leather. This means that inconsiderable deviation from determined parameters of dyeing can markedly deteriorate the quality of the dyed leather.

The data obtained have confirmed that the change in the method of liming considerably influences subsequent processes in leather processing.