A Comparative Analysis of Recovered and Commercial Carbon Black in Natural Rubber Composites: Influence of Particle Dispersion and Ash Content on Mechanical Properties

Abstract

This study compares recovered carbon black (RCB) and commercial carbon black (CCB) as reinforcing fillers in natural rubber composites, focusing on how their physical and chemical properties affect mechanical performance. RCB, derived from pyrolyzed end-of-life tires, supports circular economy goals but shows inconsistent reinforcement compared to CCB. Experimental analyses-including FTIR, particle size and ash content characterization, rheometry, abrasion, and mechanical tests were conducted to explore these differences. While RCB and CCB have similar mean particle sizes, RCB exhibits a higher z-average diameter and polydispersity index, indicating more aggregation and poorer dispersion. RCB's significantly higher ash content reduces its reinforcing effectiveness. Mechanical testing showed that CCB-filled composites outperformed RCB filled composites in tensile strength, 300% modulus, and tear resistance, especially at higher loadings (20-25 phr). In contrast, RCB-filled composites matched or exceeded tensile strength at low loadings (5-10 phr) and showed greater elongation and resilience, suggesting higher elasticity but lower rigidity. At higher loadings, RCB performance declined due to filler-filler interactions and inert residues. Tear strength characteristics also worsened under these conditions. FTIR confirmed the presence of polar functional groups on both fillers, but RCB's structural limitations offset their potential reinforcing effect.