Single-Walled and Multiwalled Carbon Nanotubes in Polybutadiene/Natural Rubber Composites Containing Silica for Conductive Green-Tire Application

This study investigates the influence of commercial single-walled (SWCNT) and multiwalled carbon nanotubes (MWCNT) on the properties of natural rubber/polybutadiene composites containing silica for green tire applications. Composites were prepared on a laboratory scale using mixing protocols simulating conventional industrial methods, varying the nanotube content while keeping a fixed silica concentration of 55 phr. First, SWCNT and MWCNT were characterized in terms of atomic composition, number of defects, and morphology. Electrical conductivity measurements on nanocomposites indicate that SWCNT achieves the percolation threshold at lower concentrations (between 8 and 10 phr) compared to MWCNT (between 10 and 13.5 phr). Electrical conductivity in the range of antistatic properties (10–4 to 10–8 S·m–1) is achieved at 10 and 13.5 phr in both cases. Differences in nanotube dispersion were observed, with SWCNT forming long bundles and MWCNT exhibiting more entangled structures. Dynamic mechanical analysis shows that SWCNT increases the storage modulus and reduces the glass transition peak width more effectively than MWCNT, indicating superior reinforcement and reduced polymer mobility. Considering the sample with good dispersion and desired electrical conductivity (10 phr SWCNT and 13.5 phr MWCNT), dynamic mechanical analysis indicated that MWCNT leads to lower values of rolling resistance than SWCNT, while wet grip improves with the addition of SWCNT. The study concludes that SWCNT provides a more efficient conductive pathway and reinforcing effect than MWCNT at equivalent loadings, offering insights into optimizing conductive elastomer composites for energy-efficient tire technologies.