Ozone utilisation for discharge printing of reactive dyed cotton
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Environmental pollution is one of the major concerns of the textile finishing sector. The reduction or substitution of the harsh chemicals used during dyeing and printing processes is necessary. In this study, the use of ozone for the discharge printing process was examined in order to substitute the use of reductive agent and caustic soda by ozone gas. The reactive dyed cotton samples were wetted by water and some selected solutions at 25%, 40% and 60% pick up were used and subjected to ozone gas treatment. The gas flow rates were 5 and 10l/min for 5 and 10min treatment times, respectively. The results were compared with that of conventional discharge printed samples. Colour discharge (%), colour difference (E), strength, washing and rubbing fastness and chemical oxygen demand (COD) values were compared and reported. Colour discharge increased at higher gas flow rates and prolonged treatment times. Although ozone printing could not attain the contour sharpness of conventional discharge printing, the addition of selected chemicals affected colour discharge and the contour sharpness. Strength tests did not show a significant decrease when using ozone treatment. Fastness tests results (washing and rubbing) were slightly higher compared with conventional discharge printed samples. COD values were much lower for ozone treatment compared with conventional discharge printing effluent. Consequently, it was demonstrated that ozone may be an environmentally friendly substitute for discharge printing.