Decoupling Hardness and Interfacial Interactions: Synergistic Origin of Wear Resistance in Natural Rubber/Carbon Black

Natural rubber (NR) suffers from inherently poor wear resistance, limiting its application in demanding environments. Conventional wisdom prioritizes filler hardness as the key determinant of wear performance. Here, we challenge this paradigm by revealing a critical synergy between filler hardness and interfacial interactions. We systematically investigated NR composites reinforced with fillers of varying hardness: Nano-Diamond (ND), Tungsten Carbide (WC), and four grades of Carbon Black (N115, N330, N550, N660). Quantitative nanomechanical mapping (PFQNM-AFM) established a hardness hierarchy of ND > WC> N115 > N330 > N550 > N660. Surprisingly, despite their superhardness, ND and WC composites exhibited inferior wear resistance. Conversely, N115, with moderate intrinsic hardness but high specific surface area, demonstrated superior wear performance. Interfacial analysis revealed that ND and WC failed to form an effective bound rubber layer. In contrast, N115 induced the formation of a robust, thick (19 nm) interfacial layer with a gradient modulus. Our findings confirm that high filler hardness alone is insufficient for reinforcement; exceptional wear resistance arises from the synergy between the filler’s structural hardness and the formation of a strong, energy-dissipating interfacial network. This work provides a theoretical basis for the rational design of next-generation abrasion-resistant elastomers.