Sulfur-Modified Carbon Nanotubes for the Development of Advanced Elastomeric Materials

Abstract

The outstanding properties of carbon nanotubes (CNTs) present some limitations when introduced into rubber matrices, especially when these nano-particles are applied in high-performance tire tread compounds. Their tendency to agglomerate into bundles due to van der Waals interactions, the strong influence of CNT on the vulcanization process, and the adsorptive nature of filler–rubber interactions contribute to increase the energy dissipation phenomena on rubber–CNT compounds. Consequently, their expected performance in terms of rolling resistance is limited. To overcome these three important issues, the CNT have been surface-modified with oxygen-bearing groups and sulfur, resulting in an improvement in the key properties of these rubber compounds for their use in tire tread applications. A deep characterization of these new materials using functionalized CNT as filler was carried out by using a combination of mechanical, equilibrium swelling and low-field NMR experiments. The outcome of this research revealed that the formation of covalent bonds between the rubber matrix and the nano-particles by the introduction of sulfur at the CNT surface has positive effects on the viscoelastic behavior and the network structure of the rubber compounds, by a decrease of both the loss factor at 60 °C (rolling resistance) and the non-elastic defects, while increasing the crosslink density of the new compounds.

Improved Heat Dissipation of NR/SBR-Based Tire Tread Compounds via Hybrid Fillers of Multi-Walled Carbon Nanotube and Carbon Black

“…A sudden decrease in the surface resistivity of samples was obtained as the MWCNT content increased to 3 phr. At a specific concentration of conductive particles, which is commonly referred to as the percolation threshold, a contiguous network of fillers is established throughout the matrix, thereby facilitating a marked transition from an insulating to a conducting state [19]. This critical threshold marks the stage at which the filler particles coalesce to form an interconnected network within the matrix.…”

“…The changes in mechanical properties are shown in Figure 7 and tabulated in Table 6. The reinforcing effect of fillers in rubber matrices is the result of several molecular mechanisms involved in this complex phenomenon: the rubber network, the hydrodynamic effect, the filler-filler interactions, and the filler-rubber interactions [19,[69][70][71]. In contrast to NR/SBR/MWCNT composites, the incorporation of carbon nanotubes has yielded a striking increase in the material properties of tensile strength within the rubber matrix.…”

“…The enhancement of properties in polymer/CNT composites primarily hinges on factors including the uniform dispersion of CNTs, interactions between the filler and the matrix, and the inherent attributes of the CNTs themselves. Due to relatively weak intermolecular forces such as van der Waals and π-π interactions that govern the assembly of CNTs, these nanotubes exhibit a propensity to intertwine, forming sizeable aggregations referred to as "bundles" [19][20][21]. The attainment of high-performance NR nanocomposites characterized by homogeneous dispersion of nanofillers necessitates the resolution of two prominent challenges: aggregation and inadequate matrix-filler interactions.…”

Elastomer Nanocomposites: Effect of Filler–Matrix and Filler–Filler Interactions

“…As mentioned by the authors, the strong dissipation of energy associated with the pronounced Payne effect displayed by CNT-based elastomeric composites prevents the large-scale use of CNTS for dynamic mechanical applications especially in the field of tires where it impacts the fuel consumption. In the work of Bernal-Ortega et al [80], MWCNTS were surface-modified with oxygen-bearing groups and sulfur in order to decrease the energy dissipation that affects the rolling resistance of tire tread compounds. A reduction in the energy dissipation and in the loss factor at 60 • C is effectively obtained in the functionalized CNTs with regard to the non-modified CNT-filled samples, but better electrical and tensile properties are displayed by pristine fillers.…”

From Nanoscale to Macroscale Characterization of Sulfur-Modified Oxidized Carbon Nanotubes in Styrene Butadiene Rubber Compounds

“…First, nanoparticles are oxidized to introduce oxygen-bearing groups on the surface using two different methods. The oxidized CNTs were then modified with sulfur . Both modified CNTs were incorporated into the SBR matrix and compared with the unmodified CNT-SBR composite with the same filler content.…”