The Influence of Zinc Stearate Complexes on the Sulfur Vulcanization of Ethylene–Propylene–Diene Monomer

This article explores the influence of synthesized zinc stearate (ZnSt) complexes with different molar ratios of zinc oxide (ZnO) and stearic acid (StA) on the sulfur vulcanization and properties of the ethylene-propylene-diene monomer (EPDM). The aim of study was to reduce the amount of ZnO in elastomer composites without affecting their compression set. The research involves synthesizing zinc complexes, including the addition of sulfur, and using them as activators in EPDM compounds. The synthesized products were characterized using DSC and FTIR to identify their composition and thermal properties. The results of the compression set and equilibrium swelling tests indicated that ZnO was used in excess as an activator. Zinc complexes allowed for a significant reduction in zinc content compared to ZnO. The stoichiometric salt of ZnO and StA was the most effective in terms of vulcanization parameters and the compression set. Non-stoichiometric complexes were less effective, proportionally to their content. SEM images showed that the dispersion of components was relatively homogeneous in vulcanizates with active ZnO and commercial ZnSt. However, the blooming of ZnSt from vulcanizates was observed. Thus, using synthesized materials could reduce the zinc content in EPDM composites while maintaining good properties, but a further reduction is needed to avoid blooming.