Towards the chemical upgrading of the recovered carbon black derived from pyrolysis of end-of-life tires

This work deals with the recovered carbon black derived from the industrial-scale pyrolysis of end-of-life tires, targeting at increasing the technical knowledge to be considered as alternative to the virgin carbon black. Accordingly, a demineralization process using HCl, HNO₃ and NaOH to improve the properties of the recovered carbon black is investigated. A fractional factorial design 2^k-2 showed that the acid concentration has the highest statistical influence on the ash reduction. At 5 M, the ash content was 6.12 wt% and 5.21 wt% for HCl and HNO₃, respectively. The demineralized recovered carbon black obtained from both acids together with a reference carbon black (N550) were characterized by elemental and proximate analyses, surface area, ash composition by XRF, and morphology by SEM and TEM. A comprehensive surface chemistry analysis by FTIR and TPD-NH₃ was also conducted. In addition to decreasing the ash content and to increasing the surface area, the recovered carbon black treated with HNO₃ led to the highest presence of acidic functional groups. In this regard, this upgraded recovered carbon black is expected to offer both better filler/polymer interaction and in-rubber performance, as compared to the non-treated recovered carbon black. The experience gained from this work provides important impetus to deem the recovered carbon black as alternative to virgin carbon black, and paves the way to close the end-of-life tire-recycling loop by both pyrolysis and chemical upgrading strategies.