Synthesis of ZnO/Al2O3 from Bohemite via the Impregnation Method and Its Potential as an Activator in Rubber Vulcanization

The study synthesized and investigated ZnO/Al2O3 composites as potential activators for rubber vulcanization. Al2O3 was initially prepared from boehmite, followed by ZnO deposition via wet impregnation with varying Zn(NO3)2 solution concentrations. This approach yielded a series of composite 10%, 15%, 20%, 25%, 30%, 35%, and 40% ZnO. Comprehensive characterization was conducted using X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area analysis, particle size distribution, and scanning electron miscroscopy (SEM). XRD analysis confirmed the formation of g-Al2O3 and the deposition of nano-sized ZnO onto the Al2O3 surface. SEM examination demonstrated that the porous structure of Al2O3 was preserved, particularly in the in 20% ZnO/Al2O3 sample, which was therefore was selected for the natural rubber (NR) vulcanization study. The NR compound containing 10 phr of 20% ZnO/Al2O3 exhibited a steady torque increase over time, with an extended optimal cure time compared to compounds containing conventional ZnO (2 phr) and Al2O3 (8 phr) individually and their physical mixture. Despite the longer cure time, this formulation achieved superior tensile strength and elongation at break. These improvements are attributed to the synergistic effects between ZnO and Al2O3, where ZnO promotes crosslink formation while Al2O3 helps suppress the overcuring typically caused by ZnO.