Rethinking Biochar Reinforcement Role in Elastomer Composites for Greener Tire Manufacture

Carbon black (CB) production in tire manufacturing has prompted the search for sustainable alternatives to address the environmental concern related to its fossil origin. Replacing fossil CB in the rubber industry is imperative for reducing the environmental footprint of vulcanized elastomer composites used in tire treads, especially in the current circular economy and decarbonization scenario. In this study, we investigate the potential use of biochar as an elastomer reinforcing agent by substituting CB in natural rubber/styrene−butadiene rubber (SBR) composites. Three varieties of biochar, derived from oilseed rape straw, miscanthus straw, and softwood pellets, were incorporated at 30, 50, and 70 phr by replacing the CB counterpart. Detailed physicochemical characterization was performed using FTIR, DLS, BET surface area analysis, and SEM to elucidate the role of morphological and structural parameters such as porosity, particle size, surface chemistry, and aromaticity in filler−matrix interaction. Mechanical and dynamic mechanical analyses suggested that biochar does not follow the classical CB reinforcement paradigm, where the surface area and particle size are dominant. Instead, reinforcement is a result of specific oxygen-containing surface functional groups in the biochar mesoporous architecture, which mediate the polymer−filler entanglement. Among the studied materials, oilseed rape straw biochar pyrolyzed at 700 °C (OSR700) exhibited optimal dispersion, superior interfacial adhesion, and the best balance between tensile strength (3.8 MPa) and toughness (1380 MJ m−3). In contrast, softwood-derived and lower-temperature biochar showed poor dispersion and limited reinforcement due to unfavorable pore size or excessive hydrophilicity. The research demonstrates that tailored biochar represents a promising, scalable, and environmentally sustainable alternative to carbon black in tire manufacturing. This innovation has the potential to produce high-performance tires with a significantly reduced environmental footprint. Moreover, the implications of this study extend beyond the tire industry, offering valuable insights for sustainable composites, energy dissipation materials, and green polymer engineering.