We explore the impact of carbon black on the structure–property relationships of natural rubber (NR) during thermo-oxidative aging. NR samples containing 27% mass of carbon black were subjected to aging in air at temperatures ranging from 70 to 115 °C for up to 270 days. The aging process was monitored in terms of oxygen consumption, swelling, and tensile testing. Results revealed a substantial reduction in crosslink density, highlighting chain scission as the dominant process. Tensile properties were significantly affected, showing decreases in modulus, elongation at break, and stress at break. A comparison with previous studies on unfilled NR shed light on the role of carbon black during oxidation. Our findings suggest that carbon black plays a minor role in macromolecular network modifications for similar exposure conditions. More specifically, we analyze the validity of structure–property relationships between the average crosslink density and mechanical properties during thermo-oxidative aging regardless of whether the elastomer contains carbon black filler. These results illustrate a new strategy for studying the aging of filled elastomers.

  • Carbon black does not affect macromolecular network changes during the thermo-oxidative aging of natural rubber.

  • Coupling the Medalia equation and classical rubber elasticity theory accurately captures changes in the modulus of carbon black–filled natural rubber.

  • Decrease in elongation at break is effectively described by established structure–property relationships.

  • Filler–matrix interactions remain unaffected by oxidation.

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