Understanding the Effect of Zinc Oxide (ZnO) With Carbon Black Coupling Agent on Physico-Mechanical Properties in Natural Rubber Matrix

Natural rubber (NR) is not only the main compounding ingredient used to make the majority of components of tires as well as other rubber products, as it plays a significant role in ensuring that they operate well and complies with environmental standards. The applications of NR products are limited to high temperatures due to the revision tendency of NR vulcanizate. To address these issues, the potential engagement of a carbon black (CB) coupling agent (CA) in the presence of metal oxide i.e. Zinc Oxide (ZnO) was investigated in an NR-based system. This CA has dual functionality on physicomechanical properties. CA has the ability to reduce hysteresis loss as well as improve anti-reversion properties and these properties thoroughly depend on the presence of ZnO. While ZnO was added to the master formulation, a 65% improvement in reversion properties was observed. On the other hand, while ZnO fully transferred to the final formulation, bound rubber (BR) content increased by 19%, the difference in storage modulus (ΔG’) is reduced by 22%, cure rate index (CRI) improved by 14%, loss tangent (tan δ) reduced by 18% and slightly improve in elongation at break compared to control compound. Thermo-gravimetric analysis (TGA) was engaged to understand the thermal stability and degree of purity of CA. A differential Scanning Calorimeter (DSC) was used to detect the phase transition of CA. Fourier Transform Infrared Spectrum (FTIR) was adopted to detect the presence of carboxyl and amine groups in the CA moiety. Payne effect, BR content and Transmission Electron Microscope (TEM) were employed to investigate the micro-level dispersion of CB in the natural rubber (NR) matrix.