Synergistic effect of zinc ions from tire waste and modified zinc oxide on mechanical, thermo-mechanical and antibacterial properties in epoxidized natural rubber composites
Napasorn Kingkohyao, Tanit Boonsiri, Jobish Johns, Raymond Lee Nip, Yeampon Nakaramontri
Abstract
Blends of tire waste (TW) and epoxidized natural rubber (ENR) filled with zinc oxide absorbed on silica surfaces (ZnO-SiO 2 ) 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 (Zn 2 + ) released from TW and ZnO-SiO 2 , which played a critical role in enhancing the overall performance of the TW/ENR composites. The presence of Zn 2+ remained from TW contributed to increased crosslink density and modulus during increasing TW concentration in the blends, while the Zn 2+ from ZnO-SiO 2 can both support crosslinking propagation and enhanced the antibacterial properties by facilitating a controlled release of active Zn 2+ regarding well ZnO dispersion and distribution within TW/ENR matrix. The chemical combination, in particular the remained ZnO in TW and ZnO-SiO 2 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 Zn 2+ from TW and ZnO-SiO 2 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 Zn 2+ from TW and ZnO-SiO 2 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. • Effect of Zn 2+ in TW blends on antibacterial efficiency is first examined. • Effects of remained ZnO and additional ZnO-SiO 2 was clarified and modeled. • Synergistic of Zn 2+ ions in TW and ENR can activate crosslinks in the blend. • TSSR was used to clarify crosslinks and decomposition of sulfur bonding. • Antibacterial of 99.9 % in 24 h from TW/ENR/ZnO-SiO 2 composites was achieved.