Sustainable ultrasound-assisted ultra-low liquor ratio dyeing of wool textiles with an acid dye

Conventional wool dyeing is an energy-hungry process as the dyeing is carried out at boil using a high liquor ratio. It can be energy efficient if dyeing can be carried out at low temperatures or if the liquor ratio can be reduced. Ultra-low liquor ratio dyeing (materials to liquor ratio 1:5) is advantageous as it considerably reduces consumption of auxiliary chemicals and energy in dyeing. However, at that low liquor ratio dye molecules form agglomerates causing low dye-uptake and uneven dying. In this work, the feasibility of using ultrasound in conjunction with a range of textile auxiliaries for the prevention from dye agglomeration has been investigated for the dyeing of wool with an acid dye. Three ultrasonic baths with different ultrasonic power were used to investigate the effect of ultrasonic power on dyeing performance. It was found that citric acid in conjunction with ultrasound prevented the formation of dye agglomeration in a dyebath, and also produced deeper shades and uniform dyeings compared to the dyeing without ultrasound. The depth of shade increased with an increase in ultrasound power. The application of ultrasound did not cause any loss in tensile strength of the fabric, suggesting there was no fiber breakdown. The developed technique could be used in textile industry to make wool dyeing even more sustainable than it is at present.