Green approach to denim waste recycling using N-methylmorpholine N-oxide and deep eutectic solvent for regenerated cellulose

Denim, primarily composed of cotton-based cellulosic fibres, represents a major textile waste stream. Efficient, eco-friendly dissolution and regeneration methods are essential for sustainable recycling. This study investigates a novel ternary solvent system (NCM) comprising N-methyl morpholine-N-oxide monohydrate (NMMO), choline chloride ([Cho]Cl), and malic acid (MA) for its ability to dissolve denim waste and regenerate cellulose. Molecular dynamics (MD) simulations showed that the deep eutectic solvent (DES) component ([Cho]Cl-MA) enhances cellulose solubility by disrupting its native hydrogen-bond network and promoting solvent-cellulose interactions. Experimental characterisation confirmed these effects. FTIR spectroscopy showed preserved cellulose functional groups with subtle changes in hydrogen bonding. Rheological testing revealed increased viscosity in the NCM system, suggesting stronger intermolecular interactions. SEM images indicated greater surface roughness and porosity in regenerated films, consistent with reduced crystallinity. TGA showed a slight decrease in thermal stability, likely due to residual DES. XRD confirmed a more complete transformation from cellulose I to cellulose II and lower crystallinity, supporting enhanced dissolution. Notably, denim dissolution occurred at 80 °C significantly lower than the 110 °C required for NMMO alone and without the need for stabilisers like propyl gallate, improving process sustainability. Solvent recovery exceeded 95%, with FTIR confirming the chemical integrity of the recycled solvent. These experimental results closely aligned with MD simulations, providing a comprehensive understanding of the NCM system’s role in cellulose dissolution and regeneration. Overall, the NCM solvent system offers a greener, more efficient alternative for recycling denim waste into regenerated cellulose materials. • Ternary NMMO/[Cho]Cl/MA solvent dissolves denim at lower temperature without stabilisers. • DES boosts cellulose dissolution by reshaping H-bond networks, confirmed by MD simulations. • Regenerated films exhibit novel porous morphology with 95% solvent recovery achieved.