Graphite reinforced polymers for sealing geothermal wells

The objective of this study is to develop high-temperature resistant polymers for sealing geothermal wells by reinforcing inexpensive rubber with surface-treated graphite particles. We respectively treated two types of graphite particles, small-size lamellar graphite (SFG15) and graphite nanoplatelets (GNP), with a mixture of sulfuric and nitric acids. Through surface treatment, carboxylic groups are shown to be formed on graphite surfaces, and their oxygen contents are considerable. Polymer nanocomposites were made by compounding treated graphite particles with ethylene propylene diene monomer (EPDM). Uniform dispersion of treated graphite within developed polymer nanocomposites was achieved. Direct heating of prepared EPDM nanocomposites shows that treated SFG15 and GNP both enhance the temperature resistance of EPDM by over 80 °C. Also, the addition of treated graphite to EPDM remarkably enhances its storage modulus. Among all additive types and concentrations, 3.0 wt.% of treated SFG15 performs the best in enhancing the storage modulus (by up to 215.83%) and reducing tan δ, namely the loss factor. Adding treated graphite significantly enhances the specific heat capacity of EPDM and remarkably increases the heat energy required to melt it. The onset degradation temperature of EPDM-SFG15 nanocomposites is 30 °C higher than that of plain EPDM. With these enhanced thermal and mechanical properties, the prepared nanocomposites are a promising candidate for the constituent polymer of seals applicable in geothermal wells.