Supercritical carbon dioxide as a green media for simultaneous dyeing and functionalisation : A study on disperse dyeing and silicone functionalisation for water repellency of polyester fabric

Abstract: Textile processing methods such as conventional exhaustion dyeing, pre-treatments and printing consume high amounts of water and use partly toxic and hazardous chemicals which are non-degradable. These chemicals (e.g. excess amount of dye, additives and catalysts) remain partially in the waste-water which is drained out and ends up polluting the environment. The supercritical carbon dioxide dyeing technology presents an eco-friendly and water-free method with reduced use of chemicals and energy. The benefits of such technology are currently not overcoming the relative high investment costs which impede its full implementation into the textile industry. This study presents an approach to extent the application of the eco-friendly supercritical carbon dioxide technology. It combines the well-studied supercritical carbon dioxide dyeing process for polyester with the functionalisation process to obtain water repellent surface properties. As water repellent (substance) environmentally benign silicones are used. Results showed that the simultaneous dyeing and functionalisation process was feasible assessed by the compatibility of the dye and silicone in the system. Silicone and dye did not interfere in each other’s functionality (colour strength and water contact angle). Further the process temperature and silicone molecular weight showed no influence on the colour strength of the fabric whereas the water contact angle (water repellence) increased with increasing temperature. The resulting polyester fabric showed acceptable colour strength yet did not obtain sufficient water repellent properties despite the increase in water contact angle of the treated samples to the untreated reference sample. The poor water repellence is suggested to be caused by the hydrophobic functional groups of the silicones oriented towards each other rather than toward the outer fabric surface. Overall the thesis is promoting research which combines eco-friendly technologies including environmental benign chemicals for the textile industry. Silicones are widely used in textile processing not only as water repellents, but also as anti-foaming agents, lubricants and softeners. Therefore a water-free and eco-friendly application method can benefit a wide range of finishing processes.