Integrating Structural, Dielectric and Mechanical Properties to Evaluate the Performance of NR/SBR/GTR/SiO₂ Compounds

The incorporation of ground tire rubber (GTR) into elastomeric compounds offers a sustainable route for recycling end-of-life tires; however, its effect on the structure-property relationships governing mechanical and dielectric performance remains insufficiently understood. In this study, NR/SBR composites containing 0-50 phr of devulcanized GTR were prepared and characterized through Fourier-transform infrared spectroscopy (FTIR), swelling analysis, thermogravimetric analysis (TGA), mechanical testing, and broadband dielectric spectroscopy. FTIR and swelling results revealed enhanced matrix-GTR interaction at intermediate GTR loadings (10-20 phr), evidenced by an increased intensity of sulfur-related bands and reduced swelling degree, indicating partial chemical integration of the recycled phase into the elastomer network. Mechanical testing showed that increasing GTR content increased stiffness at high loadings, while tensile strength, elongation at break, and toughness progressively decreased due to interfacial debonding mechanisms. TGA demonstrated that the main degradation temperature of the NR/SBR matrix remained essentially unchanged (418-425 °C) across all formulations, confirming preservation of thermal stability despite increasing structural heterogeneity. Dielectric spectroscopy (10^-2-3 × 10⁶ Hz, 40-120 °C) revealed pronounced Maxwell-Wagner-Sillars interfacial polarization and thermally activated charge transport, with conductivity increasing with GTR content without evidence of electrical percolation, even at 50 phr. The results demonstrate that the performance of NR/SBR/GTR/SiO₂ composites is primarily controlled by the interfacial structure generated by the recycled phase. Intermediate GTR contents (10-20 phr) provide the most effective matrix-GTR interaction, while higher loadings mainly affect mechanical integrity and dielectric response through increased structural heterogeneity. These findings provide practical guidelines for designing sustainable elastomeric compounds with high recycled content while maintaining thermal stability and controlled electrical insulation properties.