Adsorption and Kinetic Study of Cochineal Dyeing on Wool Using Different Mordants

Cochineal or carmine is a natural red dye that is extracted from an insect, and used worldwide as a food and textile dye. The cochineal dye permanently sticks to the wool fabric in the presence of a mordant- a metallic ion that forms a coordination complex with the cochineal dye and binds the cochineal dye onto the wool fabric.

In this project, the adsorption kinetics and thermodynamics of cochineal dye on wool fabric were studied. Thermodynamic and kinetic parameters were determined by analyzing the dyeing process at different temperatures. Three mordants were used: tin, alum and copper to determine their effect on the model parameters. The mechanism of adsorption of cochineal dyeing onto wool was investigated using the pseudo first-order and pseudo second-order kinetic models. The adsorption kinetics were found to follow a pseudo first-order kinetic model for all the mordants. The adsorption data of cochineal dye on wool were analysed by the Langmuir and Freundlich models. The results indicate that Freundlich model provides the best correlation for all the mordants.