Hydrated Deep Eutectic Solvents for the Sustainable Valorization of Textile Waste

A series of new deep eutectic solvents (DESs) was prepared to enable a greener approach to cellulose recovery from cotton products and textile waste. In this context, while choline-based binary DESs have been extensively investigated, alternative systems, especially metal-based hydrated DESs, have received less attention. In this work, four novel ternary DESs were synthesized using (i) ZnCl₂ or CaCl₂ and (ii) lactic acid or tartaric acid, (iii) with water added as a third component. By combining the hydrogen bond-disrupting capacity of traditional binary DESs with the lubricating-modifier and stabilizing effects of water, low-viscosity DESs, stable at room temperature, were obtained. These systems demonstrated remarkable versatility in processing cellulose from different sources, enabling complete dissolution of microcrystalline cellulose (MCC) and extensive structural disruption of cotton fibers to recover regenerated cellulose or nanocellulose (NC). The DES formulations were characterized through thermal and rheological analyses, including differential scanning calorimetry (DSC). The thermal stability, morphology, and structural changes of the processed cellulosic materials were investigated using thermogravimetric analysis (TGA), Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), polarized light microscopy (PLM), and electron microscopies (TEM and SEM/EDX). Overall, these results highlight the potential of earth-abundant, cost-effective metal-based DESs for the sustainable valorization of cotton-derived waste.