Deep eutectic solvent-assisted bacterial devulcanization, detoxification, and degradation of waste tyre rubber

Abstract

The biodegradation of waste tyre rubber (WTR) is hindered by the presence of sulfur and additives, which limit microbial mineralization of the rubber polymers. To overcome this constraint, a hybrid chemi-biological approach is developed, wherein pretreatment with a reusable choline chloride/urea (ChCl/Ur) deep eutectic solvent (DES) is employed. Ground tyre rubber (GTR) is subjected to DES-assisted thermochemical pretreatment, followed by biological treatment using the Rhodococcus rhodochrous RPK1 bacterial strain in mineral salts medium for 28 days. The DES pretreatment significantly enhances biodegradation efficiency, resulting in a significant improvement over biological treatment alone. Structural, elemental, and thermal analyses confirm partial devulcanization, cleavage of sulfur crosslinks, removal of zinc additives, and reduced thermal stability. Crosslink density decreased by 43.6%, and Horikx analysis indicates a mixed degradation mechanism. The results demonstrate that DES pretreatment effectively reduces limiting factors, thereby improving rubber bioavailability. This hybrid strategy provides a viable framework for enhancing the biodegradation of WTR and supports a sustainable rubber recycling pathway.