Use of tetra-sodium ehtylene diamine tetra-acetate in pad-steam dyeing of cotton with reactive dyes

Reactive dyeing of cotton textiles generates high levels of dissolved solids and oxygen demands in the disposed effluent due to the use of inorganic salt (sodium chloride or sodium sulphate) and alkali (sodium bicarbonate, sodium carbonate or sodium hydroxide). Considerable efforts are being undertaken within the textile industry to reduce effluent loads and to comply with environmental regulations. This paper presents results where the inorganic salt (sodium chloride) and alkali (sodium bicarbonate or sodium carbonate) are replaced by a biodegradable organic chemical, tetrasodium ethylene diamine tetra-acetate also known as sodium edate. The dyeing method selected for the study was pad-steam in which the solution containing the dye, the salt and the alkali is applied on cotton fabric by impregnating the fabric in the solution following squeezing the fabric to a designated pick-up of solution and steaming to achieve penetration and fixation of the dye to the fibres within the fabric. The study showed that the colour yield, dye fixation and ultimate colourfastness achieved by using sodium edate were closely comparable to those obtained using inorganic salt and alkali. An industrial trial produced the same findings where the dyeings made with sodium edate produced significant reductions in total dissolved solids; chemical oxygen demand and biochemical oxygen demand of the effluent.