Study on a cationic agent-based salt-free reactive dyeing process for cotton knit fabric and comparison with a traditional dyeing process

Since the majority of reactive dyes only have a moderate affinity for cotton, significant amounts of electrolytes are frequently needed to cause tiredness. As a result, wastewater contains significant amounts of salt and dye, and the increasing salinity of the rivers has an effect on the delicate biochemistry of aquatic life. The aim of the study was to find a sustainable dyeing process for cotton knit fabric using EPTMAC (2, 3-epoxypropyl trimethyl ammonium chloride) as a cationic agent and comparison of the cationic dyeing process (salt free dyeing) with the regular dyeing process (dyeing with salt). For this purpose, cotton knit fabric samples were dyed with reactive dyes following salt free process and with salt. Afterwards, color fastness (wash and rubbing), spectrophotometric evaluation, bursting strength test, analysis of dye bath discharge water and Scanning Electron Microscope (SEM) image of the dyed samples were carried out. Moreover, water consumption was also evaluated for the both cationic and regular dyeing process. In terms of color fastness, cationized dyed fabric showed no change to a slight loss in depth (rating of 4-5) for both wash and rubbing fastness. From the spectrophotometric evaluation, it was found that cationized dyed fabric appeared darker and less yellowish tone. Moreover, in case of bursting strength, cationized black, hot pink, and light pink colored fabrics possessed bursting strengths of 287 kPa, 337 kPa, and 440 kPa, correspondingly. After analysis of dye bath discharge water, Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Total Dissolved Solids (TDS) value of regular colored water samples were 45%, 39%, 54% greater than that of cationized dyed water samples respectively. Cationized dyed water value for Dissolved Oxygen (DO) was 6.39 mg/l, which was within the acceptable limit. The SEM image asserted that the cationized colored samples had consistent dye dispersion, greater adhesion, and no dye anomalies. Considering water consumption, it was found that 37%, 27% and 23% less amount of water required for dyeing dark, medium and light shade of cationized samples due to fewer washes after dyeing and elimination of fixing steps. In addition of that, total cost of cationic dyeing process was less due to less chemical consumption, less utility use, shorter process time and less amount of dyes needed. Cationic dyeing process is a sustainable practice of dyeing cotton fabric with reactive dyes that offers numerous advantages when compared to the regular dyeing process with less cost consumption and low amount of environmental pollution.