ABSTRACT Natural rubber (NR) composites reinforced with silica, carbon black (CB), and graphite were prepared as single-filler and hybrid-filler systems to investigate how filler type and hybrid composition influence cure behavior, mechanical performance, electrical resistivity, and morphology before and after thermal aging. The compounds were prepared using a two-roll mill followed by vulcanization. Cure characteristics were evaluated by moving die rheometry using ML, MH, and the torque increment ΔM (MH − ML) as indicators of compound structuring and effective network development in filled systems. Mechanical properties were assessed through 100% modulus, tensile strength, elongation at break, hardness, and compression set, while volume resistivity measurements were used to evaluate insulating and conductive network formation. SEM observations were employed to examine filler dispersion and interfacial characteristics. Silica improved electrical insulation and maintained higher extensibility, whereas CB produced the strongest reinforcement with the highest modulus and hardness. Graphite alone provided limited reinforcement due to its larger particle size and weaker interfacial interaction; however, its performance improved in hybrid systems with CB or silica. Hybrid filler formulations, particularly silica/CB and CB/graphite systems, provided higher modulus and tunable electrical behavior compared with single fillers, especially at a total filler content of 45 phr. These results demonstrate that optimized hybrid filler systems can enhance the multifunctional performance of NR composites and provide formulation guidance for applications such as vibration isolators, conductive elastomers, and structural rubber components.
Watthanaphon et al. (2026) studied this question.