Synchrotron X-ray Nano-CT Reveals the Dynamic Reinforcement Structure of Pyrolytic Carbon Black from Sustainable Tire Recycling

Due to its considerable economic viability and environmental benefits, pyrolysis carbon black (CBp) from waste tire pyrolysis is receiving growing attention for sustainable resource management. However, its application is significantly hindered by its weak reinforcement. To investigate the factors contributing to its weak reinforcement compared to commercial CB, in this work, the dynamic structural evolutions of commercial N660, CBp, and CBp activated with bis[3-(triethoxysilyl) propyl] tetrasulfide (TESPT, denoted as aCBp) in natural rubber (NR) under strain were investigated in situ using synchrotron radiation X-ray nano-computed tomography (Nano-CT). Results showed that the aggregates of N660, with a rough surface and rich branches, sufficiently contacted each other to form a well-developed filler network, and underwent network deformation and low aggregate breakage under stretching. In contrast, CBp exhibited low surface activity and few branches due to its surface covering residues. The weak contacting branches that led to the formation of a fragile network underwent extensive breakage during stretching. For aCBp, the improved surface activity enhanced branch contacts. It experienced network deformation at low strains and serious breakage at high strains, which is consistent with the hypothesis that interfacial adhesion may be stronger than interparticle adhesion. The tangent modulus of aCBp increased by 9.1% at a strain of 0.5 compared to CBp, suggesting that the surface modification improved the tangent modulus by enhancing the interparticle and rubber–filler interactions. This finding provides a new insight for improving CBp surface modification, enhancing its reinforcing performance and advancing the circular economy of waste tires.