Study on a water-saving and salt-free reactive dyeing of cotton fabrics in non-aqueous medium of liquid paraffin system

Abstract

Aiming at solving the problems existed in conventional cotton dyeing with reactive dyes, such as low dye-uptake, high salt-consumption, and large wastewater-emission, a water-saving and salt-free reactive dyeing of cotton fabrics in non-aqueous medium system was studied. The effect of pickup rate, alkali concentration and fixation temperature on color yield (K/S value) and levelness of dyed fabric was investigated, and the dyeing mechanism in non-aqueous medium system was preliminarily studied. The results showed that, the optimal dyeing process for Reactive Black KN-B in the non-aqueous medium of liquid paraffin system was as follows: pickup rate, 120%; Na2CO3 concn., 30 g/L; fixation at 75 °C for 30 min. And relatively higher Na2CO3 concn. of 50 g/L and stronger fixation conditions of 85 °C for 40 min were required for Reactive Orange K-7G. In the non-aqueous medium system, the exhaustion rate achieved almost 100% with the absence of salt and the total fixation rate reached about 90% for both Reactive Black KN-B and Reactive Orange K-7G under their optimal dyeing conditions, respectively. The high dye-uptake rate might be ascribed to ‘pushing’ force originated from the interfacial tension between hydrophilic dyes and hydrophobic paraffin oil, while the high fixation rate could be mainly due to much less hydrolysis of reactive dyes in the non-aqueous medium system. Compared to conventional reactive dyeing of cotton fabrics in the water medium, this novel dyeing technology can significantly reduce the consumption of water, chemicals and dyes, which is beneficial to lower the burden of dyeing wastewater treatment and achieve an eco-dyeing approaching.