UV and thermal degradation of tire derivatives: A comparative study of unused tires, recycled tire chips, and tire and road wear particles

Tire derivatives pose emerging environmental risks due to widespread release and pollutant content. Tire and road wear particles (TRWP), generated by tire abrasion on roads, are major microplastic sources, yet their degradation behavior and environmental impacts remain poorly understood. This study compares representative materials of tire at different stages of transformation: unused tires (UT), recycled tire chips (RTC), and TRWP, to assess how material history, particle size, and aging influence degradation and pollutant leaching. Samples underwent thermal and UV aging, with physicochemical changes characterized by FTIR, 2D-COS, and SEM, while benzothiazole leaching was evaluated as a toxicity indicator. Mass loss was influenced by particle size and surface area; TRWP showed the highest loss (2.41 % thermal vs. 0.53 % UV), followed by UT (0.66 % vs. 0.54 %) and RTC (0.43 % vs. 0.38 %). Thermal aging caused greater size reductions in UT and RTC than UV, likely due to higher crosslink density and fewer surface defects. Oxidative aging depended on material history, with pristine UT and RTC showing higher reactivity. 2D-COS revealed early degradation of surface compounds and additives, followed by polymer backbone breakdown in UT and RTC, while TRWP showed sustained changes in main rubber functional groups. Benzothiazole, a major tire additive and reliable molecular marker of tire-derived microplastic pollution, was analyzed as a representative leachable compound. UT and RTC consistently exhibited higher benzothiazole leaching than TRWP, which showed a reduction of over 99 % after 30 days. These results provide mechanistic insights into the fate and risks of tire derivatives across environmental scenarios. • TRWP are major sources of microplastics and chemical contaminants. • Degradation of tire materials depends on material type and exposure conditions. • Thermal treatment primarily caused bulk oxidation, moderate mass loss, and particle compaction. • UV aging focused on surface-limited chemical changes. • Early degradation involved surface additive loss followed by gradual polymer matrix oxidation.