A promising route to dye cotton by indigo with an ecological exhaustion process: A dyeing process optimization based on a response surface methodology

The present paper investigates a non conventional but eco-friendly exhaust dyeing process of cotton with indigo. During this process, indigo was converted to its water-soluble leuco form by a green reducing agent: the glucose, in presence of alkali and at high temperature.To improve the exhaust dyeing process, the dyeing step was carried out on modified cotton by several cationizing agents. Modified cotton fibres were characterized by Fourier transform infrared (FTIR) spectra and an X-ray diffraction analysis. The performances of the dyeing process were evaluated by measuring the bath exhaustion E (%), the colour yield (K/S), the brightness index BI (%) and the dyeing fastnesses of the coloured cotton. It was found that the colour yield and the brightness obtained from the exhaustion dyeing were improved when using cationized cotton giving fastness properties better than those obtained with untreated cotton dyed by the conventional process. The effect of the main operating conditions (cationizing agent nature and concentration, reducing temperature, dyeing duration, dyeing temperature) on the quality of this dyeing process were also studied. A surface design was employed for experimental design and optimization of results. Mathematical model equation and statistical analysis were derived by computer simulation programming applying the least squares method using Minitab 15.

► Improving the reducing power of glucose in reducing indigo.
► Study the effect of modified cotton on the dyeing process.
► Optimization of an exhaust green dyeing process with indigo.