In the present work, uncured and cured properties of high-performance, sustainable Natural Rubber nanocomposites developed by leveraging the unique synergy between carbon black and fibrous nanofillers such as silicon carbide, carbon nanotubes, and aramid nanofibers were investigated. Reinforcement in these composites was analyzed using the properties of the unvulcanized compounds, which were then correlated with those of the vulcanized compounds. A 50% increment was recorded for the bound rubber content of the nanocomposites, which resulted in tremendous improvements in the reinforcement index and tensile strength of the unvulcanized nanocomposites. In contrast, the die swell index came down compared with the control compound. The formation of a percolating network due to the presence of high aspect ratio fibers resulted in a higher Payne effect in hybrid nanocomposites, which was confirmed from the scanning and transmission electron microscopy. The 100% modulus, 300% modulus, and tensile strength of the unvulcanized nanocomposites recorded an improvement of 80, 121, and 450%, respectively, by the incorporation of nanofibers. The molecular aspects of reinforcement were elucidated from theoretical calculations using Mooney-Rivlin plots. It was presumed that the improved reinforcing efficiency of the nanofibers resulted from restricted mobility of elastomer chains due to the presence of the dual filler system.

The specific geometry and distinct properties of one-dimensional nanostructures make them the most ideal candidates as reinforcing elements in composites and the dependence of physical, mechanical, thermal, and wear properties of polymer composites on their dimensionality, nature, and dispersion is interesting. The upsurging demands for high-performance elastomer composites require the application of such nanomaterials as reinforcing agents. Here, we offer a detailed characterization of some of the novel fibrous nanofillers such as silicon carbide nanofibers, aramid nanofibers, carbon nanotubes, and graphite nanofibers. Morphology, crystallinity, surface chemistry, polarity, and thermal stability of these nanofibers were analyzed using techniques such as electron microscopy, X-ray diffraction, infrared and Raman spectroscopy, and thermogravimetric analysis. Natural Rubber nanocomposites were developed using these fibrous nanofillers, and their rheometric, mechanical, dynamic mechanical, and thermal properties were studied. ANF-reinforced compounds gave the highest increment in 300% modulus while the highest tensile strength was obtained by CNT reinforced compounds at 4 phr filler loading. CNT and GNF-reinforced compounds improved the wear resistance simultaneously by 43% and 33% respectively, while SiC and ANF improved it by 10% and 8% respectively. Lower tan delta and better thermal stability were also recorded.Future exploration may involve the use of these nanofibers in conjunction with carbon black or silica to achieve high-performance elastomer compounds for real-life applications.

Hybrid nanocomposites were prepared by predispersion of new nanofibers such as aramid nanofibers, carbon nanotubes, silicon carbide nanofibers (SiC), cellulose nanofibers, and graphite nanofibers in natural rubber (NR) latex prior to melt mixing in an internal mixer to ensure the exquisite dispersion of nanofibers in NR. The competency of these nanofibers in reinforcing NR as well as enhancing its barrier properties has not been widely investigated. The fabricated nanocomposites showed enhanced curing as well as mechanical and dynamic mechanical properties. Morphology of the composites was analyzed through electron microscopy. The increase in tortuosity created by the presence of the hybrid filler system consisting of carbon black and nanofibers was studied using permeability models. At higher tearing energies, it was seen that the nanofiber-reinforced composites showed comparable crack growth properties; however, at lower energies, the fabricated composites exhibited higher crack propagation rates compared with the control compound when studied using a tear fatigue analyzer. The improved mechanical, dynamic mechanical, and barrier properties along with comparable fatigue crack growth properties offer an opportunity to apply these systems in high-end applications such as a thinner tire inner liner with a higher NR blend ratio, which can result in improved processability and reduced hysteresis, fuel consumption, and cost.

A substantial knowledge gap persists in the material development of smart tires for future self-driving automobiles, which can increase both the vehicles' performance as well as the safety of the passengers. Due to the very high stiffness of conventional strain sensors compared to the softer rubber compound used as the tire tread material, an inaccurate representation of tire deformation characteristics is anticipated. Here, a comprehensive characterization of the electrical conduction and strain sensing behavior of a natural rubber (NR)-based commercial tire tread composite combining the reinforcement of a carbon black-conductive nanofiber dual filler system was carried out for the very first time. The incorporation of as low as 2 wt.% of carbon nanotubes (CNT) and graphite nanofibers (GNF) could increase the electrical conductivity of the control compound by two orders of magnitude compared to the control compound. The gauge factor observed was much higher than the value reported for metallic or polyvinylidene difluoride (PVDF) based stain sensors developed for this application. A 25% enhancement in thermal conductivity was also observed. Thus, the developed composites have the potential to be used as in situ strain sensors so that the problems of debonding and heating differences in the sensor–rubber interfaces in tires can be avoided in future.

Reinforcement of rubber by nanofillers has been a topic of great interest in recent years. This work compares the reinforcing efficiency of nanofillers with different topologies such as spherical (carbon black and silica), fibrous (silicon carbide nanofibers and carbon nanotubes), and sheetlike (nanoclays, expanded graphite, and graphene) in two different diene rubbers (natural rubber [NR] and styrene–butadiene rubber [SBR]) at low loadings. Tensile strength improved by 88% in the case of NR and 57% in the case of SBR by the addition of just 3 phr of graphene nanoplatelets with high aspect ratio and surface area. An increase in the Mooney–Rivlin constant (C1) with filler loading variation was also observed for these filler systems in NR and SBR. The analysis of the composites using a tube model showed that the confinement of rubber chains due to the presence of fillers with a high aspect ratio gave rise to a lower tube diameter. The addition of nanofillers resulted in higher hysteresis losses, confirming their ability for higher energy dissipation. A higher Payne effect was observed in the composites due to the formation of a percolating filler network, which was accompanied by a weak strain overshoot in the loss modulus. Dynamical mechanical analysis of the composites showed a significant increase in the storage modulus of the composites at both low and room temperatures. The reduction observed in the tan δ was correlated with the crosslink density of the composites.