Development of novel and sustainable ozone based dyeing processes for cotton fabric

Textile industry uses large quantities of different dyes to fulfill the rapidly growing demand for the dyed textile products, resulting in more dye consumption, greater dye discharge as textile dyeing effluent, and higher cost. To decrease the dyes consumption, this research evaluates the performance of novel ozone-based dyeing processes for cotton fabric. So far, reported ozone-based processes for textile involve the usage of high ozone intensity for removing impurities, discoloration of solution, color fading in denim and other fabrics. This research is a first effort, which concentrates on the performance enhancement of the exhaust dyeing process for cotton fabrics through the application of controlled and lower amount of ozone. In this research, ozone dosage is controlled through ozone generator knob to only 0.5 g/h (10%), 1 g/h (20%), 1.5 g/h (30%), 2 g/h (40%), and 2.5 g/h (50%). In contrast, ozone dosage reaches up to 60 g/h in cotton bleaching. This research evaluates the four ozone-based dyeing processes for cotton fabrics using two primary reactive dyes and two primary direct dyes under different concentrations of ozone. Effect of ozonation was evaluated for both direct and reactive dyes at four stages, namely during dyeing, dry ozonation before dyeing, pre-wet ozonation before dyeing, and ozonation after dyeing. Results showed that K/S value of the optimized ozone-based processes was better than the conventional exhaust process. For instance, K/S value for benchmarked conventional dyed sample was 2.147 for reactive yellow, and it was 3.271 (33.5% higher) for the "ozonation after dyeing" process. Similar trends were observed for many other trials, resulting in higher K/S value. In addition, the fastness properties of the optimized processes were comparable with the conventional exhaust process. FTIR and SEM analysis were also performed on selective ozone dyed fabrics.