Graphite Filled Ethylene Propylene Diene Monomer Rubber for Geothermal Applications

The working temperature of a geothermal well can be much higher than that of oil and gas wells, which can degrade and decompose the constituent polymer of seals used for the purpose of zonal isolation. To ensure the geothermal well integrity, it becomes necessary to employ seals made of sustainable materials at high temperatures. Improving the thermal stability and rigidity of a polymer by changing the polymer molecular structure can be very expensive and pose some environmental challenges. To overcome these challenges and to develop seals with enhanced mechanical and thermal properties at highly elevated temperatures, we combined surface-treated graphite SFG15 particles with the inexpensive ethylene propylene diene monomer (EPDM) rubber. The surface properties of graphite SFG15 particles were treated to form strong bonding between graphite and the polymeric matrix. The X-ray photoelectron spectroscopy (XPS) analysis of treated graphite particles showed that carboxylic groups are formed on the surface of treated particles and their oxygen contents are considerable. Moreover, using the XPS analysis, we found that the bonding of carboxylic groups to the surface of graphite is stable at high temperatures. Scanning Electron Microscopy (SEM) images of EPDM-graphite (Grph) nanocomposites revealed a uniform dispersion of treated graphite within the polymeric matrix. Direct heating of the EPDM-based nanocomposite showed that treated graphite significantly improves the melting temperature of the plain EPDM. Moreover, dynamic mechanical analysis (DMA) exhibited that the addition of treated graphite to the EPDM remarkably enhances the storage modulus of the developed composite as compared to the plain EPDM. Furthermore, using thermogravimetric analysis (TGA), we found that EPDM-Grph nanocomposites possess a considerably higher degradation temperature than the plain EPDM. Results and conclusions achieved in this study can provide a reference for the development of sustainable materials to be used for the fabrication of novel seals that can stand high temperatures in geothermal systems.