Decoupling Interfacial Interactions from Crosslink Density Enables Simultaneously Low Hysteresis Loss and High Fatigue Resistance in Natural Rubber Composites

Abstract

Low hysteresis loss and high fatigue-crack resistance are simultaneously required for natural rubber/carbon black (NR/CB) composites, which directly govern fuel efficiency and service lifetime of tire products. However, they are fundamentally antagonistic dynamic properties. Current strategies to reduce the hysteresis loss mainly depend on interfacial manipulation to improve the CB dispersion. But such interfacial engineering is often coupled with an increase in crosslink density, which restricts chain mobility and inevitably compromises the fatigue-crack resistance. This coupling effect not only limits performance optimization but also obscures the intrinsic relationship between interfacial interactions and fatigue behavior. Herein, we report a molecularly tunable interfacial modulation approach that decouples interfacial interactions from crosslink density. A series of amino-functionalized polysulfides (APSs) with different amino contents but comparable sulfur ranks are synthesized via inverse vulcanization and adopted as interfacial modifiers in the NR/CB composites. The amino groups form chemical interactions with the carboxyl groups on the CB surface, and the polysulfides are covalently incorporated into the rubber chains, enabling precise regulation of the interfacial architecture without changing the crosslink density. Hence, when the amino groups increase, the CB dispersion and interfacial interactions are gradually improved, while the chain mobility is preserved, leading to a combination of markedly reduced hysteresis loss and improved fatigue resistance. More importantly, this single-variable molecular platform enables direct elucidation of how interfacial interactions control the composite microstructure and its dynamic performance. This work has thus established a generalizable framework for disentangling interfacial interactions from the network structure in filled elastomers and provided innovative molecular design principles for high-performance rubber composites.