The effect of seawater hardness on cotton fabric dyeing using reactive blue dye

Abstract Oceans are an abundant source of water; their economic potential has not yet been fully exploited. In this context, the current study aims to apply seawater in the dyeing of cotton fabrics, evaluating the influence that total hardness has on the process results. The experiments were carried out with the dye CI Reactive Blue 222 and by varying concentrations of seawater in the dyeing solution, from 0% to 100%, in increments of 10%. The results were compared with those for a conventional dyeing process with freshwater, and revealed that, even under conditions of high seawater hardness (until 6000 mg/L of total hardness), the dyeing process with seawater was able to achieve good levels of colour, only 6% lower than those obtained with freshwater. As for colour intensity, the best results were achieved when 70% or 50% seawater concentration was used in the dyeing solution. To optimise the results, a sequestering agent was added to the initial formulation with 50% seawater, with the objective of capturing the metal ions from the seawater and reducing their negative effect on the dyeing results. With the updated process recipe, the dyed samples exhibited colour uniformity, as well as excellent colour fastness indices concerning resistance to washing, seawater exposure, sweat and rubbing. Analysis by scanning electron microscopy and tensile tests was also carried out. Therefore, this research indicates that the inclusion of seawater in textile reactive dyeing processes is a real possibility. It can replace up to 50%‐70% of the freshwater used in the process, making textile dyeing more sustainable.