Mechanochemical Sulfur Functionalization of Carbon Nanotubes for Partial Replacement of Carbon Black in Tire Tread Rubber

ABSTRACT This study investigates the effects of partial replacement of carbon black (CB) with carbon nanotubes (CNTs), both sulfur‐functionalized (sCNTs) and unfunctionalized (uCNTs), in a model tire tread rubber formulation. Two CNT grades with different aspect ratios (~150 and ~7000) are functionalized via ball milling with sulfur. uCNTs and sCNTs are incorporated into rubber formulations at a 48CB:6CNT parts per hundred rubber ratio, which is a 25% reduction in total filler amount compared to a CB‐only control. SEM micrographs confirm poor dispersion of CNTs compared to CB, while sCNTs exhibit smaller agglomerates and a more uniform distribution throughout the rubber matrix compared to uCNTs. Long CNTs lead to greater increases in compound stiffness and strength than short CNTs, while sulfur functionalization further improves dispersion and interfacial bonding, resulting in enhanced tensile strength and abrasion resistance. The addition of CNTs speeds vulcanization kinetics, with sCNTs being faster than uCNTs. Dynamic mechanical analysis reveals marginal reductions in rolling resistance for compounds containing sCNTs compared to those containing uCNTs, while traction characteristics are maintained or slightly improved. These results demonstrate the potential for significant reductions in tire tread compound cost and density, supporting the design of lightweight, high‐performance rubber formulations.