Comparative Study of Recovered Carbon Black Versus Conventional Carbon Black as a Reinforcing Filler in Isobutylene‐Isoprene Rubber

ABSTRACT Pyrolysis has emerged as a cost‐effective circular strategy for valorizing end‐of‐life tires, producing recovered carbon black (rCB) as a sustainable filler alternative. This study investigates rCB as a reinforcing filler in isobutylene–isoprene rubber (IIR) composites, comparing iso‐mass (CEII‐rCBm) and iso‐volume (CEII‐rCBv) replacement strategies against a conventional carbon black (CB) reference (CEII‐CB). Ash analysis revealed an inorganic content of 16.2% in rCB, along with a lower oil absorption number and a distinct micro‐porous surface morphology observed by scanning electron microscopy. X‐ray diffraction and X‐ray fluorescence confirmed the presence of zinc and silicon, while energy‐dispersive spectroscopy identified additional impurities including calcium, sodium, and iron. Fourier‐transform infrared spectroscopy detected polar surface groups on rCB, which impaired compatibility with the non‐polar IIR and weakened the filler network, as reflected by a threefold reduction in the Payne effect measured via the rubber process analyzer. CEII‐rCBv enhanced low‐strain modulus and Shore A hardness (+18%) compared to CEII‐rCBm, although its higher filler loading reduced tensile strength by 32%, likely due to poor interfacial adhesion and micro‐defects. Despite these drawbacks, rCB‐composites maintained comparable rheology (moving die rheometer and Mooney viscosity results), supporting the feasibility of partial rCB substitution in IIR formulations, in line with circular economy goals.