Design and synthesis of novel ionic liquids for the dissolution and separation of waste poly-cotton fabrics

Ionic liquid (IL) serves as an eco-friendly solvent with significant potential to substitute toxic and environmentally harmful solvents used in the dissolution and separation of waste poly-cotton fabrics (WPCFs). Nonetheless, the inherent viscosity of ILs presents a challenge to the separation efficiency of WPCFs. To tackle this challenge, novel ILs with low viscosity were designed and synthesized in this study. Initially, the process of cellulose dissolution in five ILs was investigated by Molecular Dynamics (MD) simulations and in-situ polarized light microscope (PLM). The results demonstrated that the smaller the size of the anions and cations in ILs, the easier it is for them to penetrate the cellulose chain, interact with the hydroxyl groups on the cellulose chain, and form hydrogen bonds. Subsequently, the interaction mechanism between the five ILs and cellulose was further explored using the ¹H NMR and ¹³C NMR spectra analysis. Furthermore, rheological analysis was used to evaluate the viscosity of each ILs. The results revealed that [Mmim]MP exhibited the lowest viscosity at 25 °C, which was only 154.7 mPa s, and the wood pulp cellulose (WPC)/[Mmim]MP solution had the lowest viscosity than others. The degradation rate of [Mmim]MP-RCF was only 12 %, which was lower than some previously reported values. Ultimately, [Mmim]MP was employed for the dissolution and separation of WPCFs and the cotton dissolution rate reached 99 %, and the characterization results of the regenerated cellulose and polyester showed a superior separation of WPCFs. This research offered a potential novel solvent for WPCF recycling.