Pad-steam dyeing of cotton with reactive dyes using biodegradable alkaline organic salts
Creators: name: Khatri, Awais
Publisher: name: RMIT University
Year: 2024

description: This thesis presents the results of studies into the effectiveness of biodegradable alkaline organic salts as alternatives to traditional nonbiodegradable inorganic electrolytes and alkalis used in pad-steam dyeing of cotton with reactive dyes. The primary objective of the study was to develop improved environmentally sustainable dyeing systems. A difluorochloropyrimidine and a bis(sulphatoethylsulphone) dye were used in this study.<br><br>After early encouraging results using alkaline polycarboxylic sodium salts, it became clear that current literature and dyeing theories on the role of the electrolyte cations and anions needed further explanation for pad dyeing methods. Accordingly, studies were carried out on a range of electrolytes of different cations and anions. These studies have resulted in a new theory for dyeing of cotton with anionic dyes using electrolytes. Traditionally, industry and dye research laboratories have determined the optimum concentration for an electrolyte, in grams per litre, via laboratory tests. This research has shown that for a given cation the required concentration of an alternative electrolyte can be determined by its ionic strength, i.e. µ = ½ ∑ [molar concentration of the salt x (ionic charge)<sup>2</sup>]. In other words, having determined the optimum concentration for, say, sodium chloride, the optimum concentration of any other sodium salt is the concentration required to give the same ionic strength. These findings also lead to an improved understanding of the use of electrolytes. The driving force for dye diffusion and also dye exhaustion (exhaust dyeings) is the dyebath ionic strength; i.e. it is independent of the type of electrolyte and alkali.<br><br>In pad dyeing of cotton, dye fixation and ultimate colour yield significantly depend on the dye diffusion and the subsequent uniformity of distribution of dye molecules throughout the fibre. A hypothesis for a new and simple method of determining the extent of dye diffusion in pad dyeing of cotton with reactive dyes was proven. The new method is based on reflectance measurements for quantifying the dye diffusion.<br><br>The new theory on the role of electrolyte cations and anions and the new method for determining the extent of dye diffusion were then used in the study on a range of biodegradable alkaline organic salts as alternatives to traditional nonbiodegradable inorganic electrolytes and alkalis for pad-steam of dyeing of cotton with reactive dyes. The research presents results where any of the three biodegradable alkaline polycarboxylic sodium salts, tetrasodium ethylene diamine tetra-acetate, trisodium nitrilo triacetate and tetrasodium N,N-bis(carboxylatomethyl)-L-glutamate can be used as alternatives to traditionally used inorganic electrolyte and alkali in the pad liquor. The optimum concentrations of the organic salts were determined for dye diffusion, dye fixation and colour yield. The dye fixation, colour yield and ultimate colourfastness achieved by using alkaline polycarboxylic salts were closely comparable to those obtained by using inorganic electrolyte and alkali. More interestingly, the dyeing effluent showed considerable reductions in total dissolved solids content with the organic salts. In order to examine the applicability of the alkaline polycarboxylic salt, an industrial trial was carried out using sodium edate which gave similar encouraging results.<br>