Synergistic effect of zinc ions from tire waste and modified zinc oxide on mechanical, thermo-mechanical and antibacterial properties in epoxidized natural rubber composites

Blends of tire waste (TW) and epoxidized natural rubber (ENR) filled with zinc oxide absorbed on silica surfaces (ZnO-SiO2) were prepared via melt mixing to investigate their mechanical, thermo-mechanical, dynamic mechanical, and antibacterial properties. The study highlighted the synergistic effect of zinc ions (Zn2 +) released from TW and ZnO-SiO2, which played a critical role in enhancing the overall performance of the TW/ENR composites. The presence of Zn2+ remained from TW contributed to increased crosslink density and modulus during increasing TW concentration in the blends, while the Zn2+from ZnO-SiO2 can both support crosslinking propagation and enhanced the antibacterial properties by facilitating a controlled release of active Zn2+ regarding well ZnO dispersion and distribution within TW/ENR matrix. The chemical combination, in particular the remained ZnO in TW and ZnO-SiO2 in ENR, was found to significantly influence the mechanical properties, with ENR improving extensibility, elasticity, and mitigating blend breakage. Dynamic mechanical analysis revealed that the synergistic interaction between Zn2+ from TW and ZnO-SiO2 enhanced the composite’s relaxation modulus and thermal stability during extended curing periods. Temperature scanning stress relaxation (TSSR) analysis showed a predominance of polysulfidic crosslinks in TW/ENR blends, contributing to enhanced thermo-mechanical properties. In addition, the optimal TW/ENR ratio for achieving superior antibacterial performance against both gram-positive and gram-negative bacteria was determined to be 50:50. At this ratio, the combination of Zn2+from TW and ZnO-SiO2 exhibited synergistic antibacterial effects. The findings add value to TW, enabling its integration into various rubber composites for the development of recycled rubber products that address environmental concerns.