The Isotherms of Dyeing Wool with Cochineal Dye

Cochineal is a natural red dye extracted from an insect, and used worldwide as a textile and fabric dye. It an ideal red dye due to its brilliant carmine color, color strength and its colorfastness on many fabrics¹.  The dye permanently adheres to the fabric in the presence of a mordant - a metallic ion that forms a coordination complex with the dye and attaches it to the fabric.  Larger concentrations of mordant have been shown to improve colorfastness², but the thermodynamics of the process have not been investigated.

In this project, we studied the thermodynamics of cochineal dye adsorption on wool fabric.  Three mordants were selected: tin, alum, and copper.  Four different adsorption isotherm models were fit to the data:  Langmuir, Freundlich, Redlich-Peterson, and Temkin models.  Initial results show that the Langmuir, Freundlich, and Temkin models fit the data.  As more data is collected, we will determine the effect of mordant on the model parameters.

                                         

1. Velmurugan, P., TamilSelvi, A., Lakshmanaperumalsamy, P., Park, J. and Oh, B.-T. (2013), The use of cochineal and Monascus purpureus as dyes for cotton fabric. Coloration Technology, 129: 246–251. doi: 10.1111/cote.12032
2. Arroyo-Figueroa, G., Ruiz-Aguilar, G. M. L., Cuevas-Rodriguez, G. and Sanchez, G. G. (2011), Cotton fabric dyeing with cochineal extract: influence of mordant concentration. Coloration Technology, 127: 39–46. doi: 10.1111/j.1478-4408.2010.00276.x