Effects of the Mixing Method of Expanded Graphite on Thermal, Electrical, and Water Transport Properties of Thermosetting Nanocomposites

The present research aims to investigate the impact of various mixing techniques (centrifugal planetary mixing, ultrasonication, and high-temperature magnetic stirring) on the properties of nanocomposite epoxy resins using expanded graphite particles. Differential scanning calorimetry reveals that the curing behavior and glass transition temperature are influenced by the selected method, indicating that a suitable choice allows increasing curing degree (C.D.) and glass transition temperature up to 10% and 12%, respectively. Morphological analysis performed via Scanning Electron Microscopy and Tunneling Atomic Force Microscopy offers detailed insights into the dispersion characteristics of fillers within polymer matrices, which sensitively affect the properties of the materials. The electrical conductivity values vary by more than five orders of magnitude among the various mixing methods. Centrifugal mixing leads to a decrease in the equilibrium concentration of water (C_eq) by up to 23% compared to that of the unfilled matrix, thanks to the chemical interactions that occur between the graphitic particles and the epoxy matrix (detectable via Fourier Transform Infrared Spectroscopy). Such a reduction is strongly desired in strategic fields such as the transport sector. The analysis of the obtained results suggests choosing the dispersion method of the filler in the matrix by considering the required performance for the specific planned application.