Sustainable devulcanization and detoxification of worn-out tires using a reusable green solvent

Deep Eutectic Solvents (DESs) have gained significance as a sustainable alternative to hazardous chemicals. This study focuses on the effective applicability and reusability of choline chloride and urea (ChCl/Urea) based DES, chosen for its non-toxicity, biodegradability, non-flammability, and economic viability, aligning with the principles of green chemistry, for the devulcanization and detoxification of waste tire rubber. Notably, this is the first ever study to characterize and demonstrate the reusability potential of a ChCl/Urea DES, thereby reducing the ecological footprint of the process without compromising its effectiveness in reducing sulphur and other additives without affecting the rubber polymeric chains. Extensive characterization techniques such as Nuclear Magnetic Resonance (NMR) spectroscopy, Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR), Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive Spectroscopy (EDS), Carbon, Hydrogen, Nitrogen and Sulphur (CHNS) analysis, crosslink density determination, thermogravimetric analysis (TGA), headspace autosampler gas chromatography-mass spectroscopy (HS-GC/MS), and pyrolysis- gas chromatography-mass spectroscopy (Py-GC/MS) confirm the efficiency of spent DES and effective removal of sulphur, zinc and other additives while maintaining the rubber polymeric structure. The results show 30.86% and 32.93% total sulphur reduction, 89.83% and 92.58% zinc reduction, and 85.32% and 66.67% vulcanization accelerator reduction from waste tire rubber (WTR) using ChCl/Urea DES and spent ChCl/Urea DES, respectively. Moreover, the study confirms the biocompatibility and biodegradability of the ChCl/Urea DES. The presented process offers a scalable and environmentally benign alternative to conventional methods.