Excellent dye fixation on cotton dyed in supercritical carbon dioxide using fluorotriazine reactive dyes

Abstract

Development of a water-free dyeing process for cotton is essential for the textile industry due to ecological and economical reasons. In this study, a dyeing method is described where cotton has been effectively dyed in supercritical carbon dioxide (scCO₂). Excellent dye fixation of 100%, and colour strength (K/S) values up to 30, were achieved in a small batch reactor and in a scale-up vessel. A series of non-polar reactive dyes with fluorotriazine as reactive group were synthesised at our laboratory. Fluorotriazines were found to be the best dyes for dyeing cotton and their reaction with cotton was improved by adding small quantities of acids to the reaction medium. H₃PO₄ and HAc were tested at different concentrations on cotton dyed with fluorotriazines. Evenly dyed pieces of cotton without any damage to the cotton fibres were observed in all experiments. An important step forward has been made for the future commercialization of a green process for industrially dying cotton in scCO₂. Elimination of water and its costly treatment can be now achieved in the cotton dyeing process.