Cold Pad-Batch dyeing method for cotton fabric dyeing with reactive dyes using ultrasonic energy

► Improved colour strength and % fixation of reactive dyes using ultrasonic energy in CPB method. ► A significant decrease of four hours in batching time (from 12 hours to 8 hours) is achieved. ► The reduced batching time provides one and half time more production in the given time. ► A one third decrease in concentrations of caustic soda and sodium carbonate has also been achieved. ► This would result into a reduced chemical cost as well as a subsequent environmental benefit. Reactive dyes are vastly used in dyeing and printing of cotton fibre. These dyes have a distinctive reactive nature due to active groups which form covalent bonds with –OH groups of cotton through substitution and/or addition mechanism. Among many methods used for dyeing cotton with reactive dyes, the Cold Pad Batch (CPB) method is relatively more environment friendly due to high dye fixation and non requirement of thermal energy. The dyed fabric production rate is low due to requirement of at least twelve hours batching time for dye fixation. The proposed CPB method for dyeing cotton involves ultrasonic energy resulting into a one third decrease in batching time. The dyeing of cotton fibre was carried out with CI reactive red 195 and CI reactive black 5 by conventional and ultrasonic (US) method. The study showed that the use of ultrasonic energy not only shortens the batching time but the alkalis concentrations can considerably be reduced. In this case, the colour strength ( K/ S) and dye fixation (%F) also enhances without any adverse effect on colour fastness of the dyed fabric. The appearance of dyed fibre surface using scanning electron microscope (SEM) showed relative straightening of fibre convolutions and significant swelling of the fibre upon ultrasonic application. The total colour difference values Δ E (CMC) for the proposed method, were found within close proximity to the conventionally dyed sample.