Optimization of closed loop wet ozone process for controlled bleaching of Indigo coloured apparels through central composite design

Fashion industry is confronting a deep criticism owing to profoundly environment detrimental processing. Sustainable practices can significantly alleviate fashion’s environmental impact. Raising demand of green processing has pushed researchers to use technologies such as aerosol processing, and ozonation. Ozone is an exceptional oxidant that returns to oxygen after reaction with redox potential of 2.07V. In this study, six different denim fabrics were systematically processed through ozone in air in combination with aerosol spray technology and studied for their fade-out effects. The bleaching of denim fabrics has been investigated by subjecting them to different runs of central composite design (to corelate the influencing key parameters for optimization) constituted on three process parameters: moisture content (wt.%) in the garment, ozone (g/h) feed rate, and treatment time (min). The process time is the most significant control parameter in color strength (K/S) reduction (i.e., 20min), and a moisture pickup of 70% is optimal for effective and uniform effect at the ozone feed rate of about 28g/h. Ozone saturation inside machine also greatly limit the effectiveness of ozone fading process. In parallel, the conventional hypochlorite bleaching of denim fabrics have been carried out. It has been inferred that ozone processing is equally efficient in bleaching process as conventional process but with better retention of mechanical properties and comfort characteristics. The ozone process offers far less use of water and chemicals with better chemical and biologicals oxygen demands. Ozone processed load exhibited approximately one order less values of COD and BOD than that of hypochlorite bleaching. This methodological study establishes the fact that ozone fading process has huge potential to redefine the denim garment wet processing industry by offering the saving of a significant load of water, reduction in chemical consumption and control over indigo washdown process with better repeatability and reproducibility.