Alkoxide-based solvent dyeing: a feasible strategy for pollution minimization and sustainable approach for the reactive dyeing of cellulosic materials

Abstract

This study aimed to evaluate the feasibility of substituting the conventional inorganic alkalis (Na2CO3) with different organic alkoxide5s to explore the potential of replacing aqueous dyeing medium with environmentally friendly solvents like ethanol (EtOH). The study aimed to assess the dyeing characteristics, such as exhaustion, fixation, fastness qualities, physical properties, and environmental implications when EtOH and water were present, while also examining the impact of alkoxides. Time-gated Raman spectra provide insights into the allomorphic forms of cellulose-II after the alkoxide pretreatment, which significantly influences the overall reactivity of cellulose fibers and their dye absorption capabilities. Notably, organic alkoxide pretreated dyeing demonstrated improved color strength, exhaustion, and fixation efficiency compared to Na2CO3 pretreatment, as one of the work’s key findings. For instance, the conventional dyed fabric exhibits 3.4 times lower color strength than alkoxide-based (RR239 + C2H5ONa 3 g/L + EtOH) dyeing, showing substantial potential for upscaling at commercial level as it requires no chemical auxiliaries (such as NaCl and Na2CO3). Importantly, the alkoxide pretreatment does not significantly alter the physical, mechanical and fastness properties of the fabrics, which are comparable to both the pristine and aqueous dyed fabrics, as confirmed by scanning electron microscopy experiments. The effluent’s color intensity resulting from dyeing with C2H5ONa + EtOH (3 g/L) is approximately 24 times lower (250 Pt/Co) in comparison to the aqueous dyeing using 40 g/L of NaCl and 20 g/L of Na2CO3 in an aqueous medium (6154 Pt/Co). Apart from the color intensity, alkoxide pretreatment and EtOH-based dyeing drastically reduce the COD, BOD, TDS, TSS and total hardness values, which could have cost-saving implications for wastewater treatment plants (WWTPs).