This study presents, for the first time, a systematic investigation of the use of micronized post-consumer silica gel as a reinforcing filler in natural rubber composites, in direct comparison with commercial silicas. Thirteen formulations were prepared using three types of silica (recycled, Copasil, and ZC-185P) and three coupling agents (TESPT, VTMO, and Chartwell C-515.71HR^®). The recycled silica exhibited high purity (97.33% Si) and irregular morphology but resulted in lower crosslink density (0.47–0.59 × 10⁻⁴ mol·cm⁻³) and inferior mechanical performance, with tensile strength up to 7.9 MPa and high abrasion loss (878–888 mm³). In contrast, ZC-185P silica combined with TESPT achieved the best results, with a tensile strength of 18.5 MPa, tear resistance of 99.36 N·mm⁻¹, and minimum abrasion loss of 170 mm³. Although less efficient in reinforcement, composites containing recycled silica were successfully applied in the production of a functional rubber mat, demonstrating their practical viability. The results confirm the potential for valorization of spent silica gel as an alternative raw material for sustainable composites, contributing to the circular economy.

This study investigates the incorporation of toner residue (TR), derived from post-consumer printing cartridges, as an alternative filler in styrene–butadiene rubber (SBR) composites, with emphasis placed on solid waste valorization and the promotion of a circular economy. TR consists predominantly of fine particles containing thermoplastic polymers, carbon black, metal oxides, and additives, exhibiting functional potential as a partially reinforcing filler material. Composites containing 0 to 50 phr of TR were prepared and characterized in terms of rheometric properties, dispersion degree, elemental composition by X-ray fluorescence (XRF), crosslink density, scanning electron microscopy (SEM), infrared spectroscopy, Shore A hardness, abrasion resistance, tensile strength, and tear resistance. Rheometric results indicated modifications in vulcanization kinetics and a reduction in maximum torque for formulations with high TR contents, suggesting a possible diluent effect or interference with elastomeric network formation. Conversely, moderate TR concentrations promoted increased hardness, improved tensile strength, and higher crosslink density, associated with adequate particle dispersion within the matrix, as confirmed by SEM analysis. However, excessive TR loading led to increased abrasion loss and an overall reduction in mechanical performance. It is concluded that TR demonstrates technical feasibility as a partial substitute for conventional fillers in SBR composites, with potential industrial application, such as in footwear sole prototypes, combining functional performance with environmental impact mitigation.

This study evaluated the partial and total replacement of zinc oxide (ZnO) with magnesium oxide (MgO) in styrene–butadiene rubber (SBR) composites, as well as the incorporation of ground tire rubber (GTR), aiming to develop more sustainable elastomer formulations. Ten formulations were prepared with varying ZnO/MgO ratios (100/0 to 0/100), with and without 20 phr of GTR. The composites were characterized by particle size distribution, morphology, rheometric behavior, density, crosslink density, mechanical properties, abrasion resistance, compression behavior, and thermo-oxidative aging. The results showed that hybrid ZnO/MgO activation systems exhibited a synergistic effect, enhancing vulcanization kinetics and mechanical performance compared to single-activator systems. Total replacement of ZnO by MgO was less effective, leading to reduced crosslink density and inferior properties. The addition of GTR increased compound viscosity and altered morphology but improved abrasion and compression resistance without significantly affecting tensile strength. Aging tests indicated good thermal stability, with maintenance or improvement of tensile properties due to post-curing effects. Overall, the combination of reduced ZnO content with MgO and GTR represents a viable approach for producing SBR composites with adequate performance and lower environmental impact.