Exhaust reactive dyeing of lyocell fabric with ultrasonic energy

[Display omitted] •US energy employment significantly improved color yield (~7%) & dye fixations (~5%).•Significant in terms of NaCl 20 g/L, Na2CO3 2 g/L & 10 °C savings were obtained.•US process offered 33% higher production rate than CN exhaust dyeing process.•Chemical savings & higher production make process more economical and eco-friendly. Successful dyeing of lyocell, a biodegradable regenerated cellulose fiber, in fabric form is a challenging job. This article reports the successful reactive dyeing of lyocell fabrics with assistance of ultrasonic (US) energy via exhaust process, and compares the results with conventional (CN) exhaust dyeing process. Two commercial reactive dyes CI Reactive Red 195 and CI Reactive Blue 250 were used. Factors affecting dyeing such as fixation time, temperature and dyeing auxiliaries were compared for both processes. Under identical dyeing conditions, US dyed samples offered significantly much higher dyeing performance (i.e. color yield (>40%), dye fixation (>17%)) compared to CN process. Additionally, US exhaust process resulted in significant savings in terms of thermal energy (10 °C), capital (20 g/L NaCl and 2 g/L Na2CO3), and offered 33% higher production rate with yet improved dyeing performance (color yield up to ~7%, dye fixation up to ~5%) when compared under recommended conditions for two processes. Moreover, US dyeing poses considerably lower pollution (chemical oxygen demand 15–18% and total dissolved solids 32–36%) to the effluent in comparison to CN exhaust dyeing process. Furthermore, nearly identical colorfastness results and fiber surface morphology endorse use of US energy as a better, cost effective and relatively environment friendly technique for successful reactive dyeing of lyocell.