Effect of Expanded Modified Clay as a Secondary Filler in Silica-Filled NR Composites: Abrasion, Air Permeability, and Tread Durability

This study explores the use of modified bentonite clay as a secondary reinforcing filler in silica (SiO 2 )-filled natural rubber (NR) composites for enhanced tire tread performance. Three types of bentonite clay were examined, including unmodified bentonite clay, zinc stearate-modified bentonite clay (ZS-clay), and bentonite clay modified with both zinc stearate and di(hydrogenated tallow) dimethylammonium chloride (ZSDA-clay). The presence of modifying agents in the clay particles was confirmed by X-ray fluorescence (XRF) and Fourier transform infrared spectroscopy (FTIR), while successful intercalation and structural modification of the clay interlayers were verified through SEM and TEM analysis. Both unmodified and modified clays were incorporated into silica-filled NR formulations at varying loadings to assess their impact on key material properties, including curing behavior, filler networking, mechanical performance, thermo-mechanical stability, and oxygen barrier characteristics. Laboratory-scale evaluations revealed that modified clays, particularly ZSDA-clay, significantly enhanced filler dispersion, mechanical strength, thermal stability, and barrier properties by suppressing filler–filler interactions and strengthening filler–rubber interfacial interactions. The novelty of this work lies in the rational design of a zinc-intercalated organo-zinc clay system that functions as a multifunctional secondary filler, simultaneously acting as a reinforcing agent, dispersion modifier, and vulcanization-active component in SiO 2 -filled NR composites. To validate industrial applicability, a selected composite formulation was scaled up for motorcycle tire production, yielding promising durability test results under standardized evaluation conditions, while also highlighting remaining challenges related to abrasion resistance and groove crack formation that require further formulation optimization. • Dual-modified bentonite clay enhances silica–NR composite performance. • ZSDA-Clay improves crosslink density, dispersion, and gas-barrier ability. • Modified clays accelerate vulcanization and strengthen filler–rubber bonding. • Enhanced abrasion and thermal stability achieved with exfoliated ZSDA-Clay. • Industrial-scale tires with ZSDA-Clay show superior tread durability.