Deciphering the crosslink mechanism of dual cure EP(D)M and CTS rubber compounds for reduced oil swell

Rubber compounds containing blends of two or more polymers are common in various industrial applications, starting with the tire industry. Blends are most commonly comprising of materials that are compatible with each other. However, for blends that are comprising of polymeric materials with limited compatibility, understanding the limitation and ways to overcome it is paramount to ensuring rubber compounds homogeneity. In this study Ethylene Propylene (Diene) Polymer (EPDM) or Ethylene Propylene Polymer (EPM) and Cyclic Tetrasulfide (CTS) are combined with the goal of achieving a compound that has superior properties than EPDM or EPM. Thermodynamic studies are deployed to illustrate materials' compatibility. The role of CTS in the compound is discussed in detail, as it presents dual functions. This study represents a fundamental analysis of EP(D)M-CTS blends, starting with Thermodynamic studies and polymeric phase analysis by Scanning and Transmission Electron Microscopy (S(T)EM) hyphenated by Energy-Dispersive X-ray Spectroscopy (EDX) or Raman Spectroscopy. The resulting rubber compounds' mechanical properties are analyzed, including the Payne effect. The compound resistance against swelling when exposed to a standard hydrocarbon oil was tested on a side-by-side comparison with pure EPD and they show positive outcome. EPDM-CTS compounds have an increased resistance to swell in standard hydrocarbon oil. This feature is important in rubber articles such as for o-rings, gaskets, and other seal articles. The focus of this study is to elucidate the mechanism of crosslinking in rubber compounds comprising of EP(D)M and CTS. This fundamental understanding of the crosslinking chemical process signifies the building block for future EP(D)M-CTS compound development. • Rubber compound based on Ethylene Propylene (Diene) Polymer (EP(D)M and Cyclic Tetrasulfide (CTS). • Polymeric phase compatibility – thermodynamic studies. • Scanning and Transmission Electron Microscopy (S(T)EM) hyphenated with Energy-Dispersive X-ray Spectroscopy (EDX) or Raman Spectroscopy used for analyzing rubber compounds. • Detailed mechanism of crosslinking. • Dual cure rubber compound with superior resistance to swell in hydrocarbon media than EP(D)M.