# Mechanical and Conductive Behavior of Graphite Filled Polysulfone-Based Composites
## 2 Materials and Methods
### Characterization  
Scanning electron microscopy (SEM, TESCAN VEGA, Brno, Czech Republic) was used to examine the fractured surface of the composite in order to evaluate the dispersion of the graphite particles. According to ISO 1183-1:2019 (Plastics--Methods for determining the density of non-cellular plastics), sample density was measured by hydrostatic weighing in distilled water and ethanol using an AND GR 202 analytical balance (AND, Japan) supplied with a hydrostatic weighing attachment AD-1653. The sample was weighed in air with a 0.001 g precision to measure its density. At a temperature of 20 \(\pm\) 2 \({}^{\circ}\)C, 150 mL of ethyl alcohol or distilled water was put into the cylinder and then after placing the sample in the liquid, it was weighed again. Sample density in g/cm\({}^{3}\) is calculated using the formula  
\[\rho=\frac{\mathrm{A}}{\left(\mathrm{A-B}\right)}*\rho_{0}\]  
where \(\rho\), A, B and \(\rho_{0}\) are density of the sample g/cm\({}^{3}\), sample's weight in the air g, sample's weight in the water g and density of distilled water g/cm\({}^{3}\), respectively. The additivity rule was used to calculate the porosity based on the real density of the polymer (1.234 g/cm\({}^{3}\)) and the ideal density of a single graphite crystal (2.27 g/cm\({}^{3}\)). The resulting samples have defects inside the graphite particles as well as porosity along the polymer-filler interfaces, since the true density of the graphite particles is always lower than the density of a single crystal. As a result, a rise in overall porosity is connected with an increase in the amount of the material's fillers, which have their own nanosized porosity at a level of 12-15%. The LFA 447 Nanoflash diffusivity instrument (Netzsch-Geratebau GmbH, Selb, Germany), which is based on a xenon flash lamp and complies with ASTM E1461, was used to measure the thermal conductivity of the additive-filled polymers. On one side, a test sample is consistently subjected to a single xenon flash tube pulse. Using an infrared detector, the temperature increase on the other side is monitored over time. On the basis of the geometry of the temperature rise curve, the thermal diffusivity may be calculated right away. For the purpose of measuring thermal diffusivity, the samples were heat-pressed at 160 \({}^{\circ}\)C, 194 kN, for 20 min into cylinders with a diameter of 12.7 mm and a thickness of 2 mm. The thermal conductivity was then determined using the formula shown below:  
\[\lambda=\mathrm{a}\cdot\rho\cdot\mathrm{Cp}\]  
where \(\lambda\), \(\mathrm{a}\), \(\rho\) and \(\mathrm{Cp}\) are thermal conductivity \(\mathrm{W/(m\cdot K)}\), thermal diffusivity \(\mathrm{mm^{2}/s}\), material density g/cm\({}^{3}\) and heat capacity j/(g \(\cdot\) K), respectively. Experimental determination of the specific heat \(\mathrm{Cp}\) of composite materials for the range from 25 to 250 \({}^{\circ}\)C was carried out using a differential scanning calorimeter NETZSCH DSC 204 Phoenix F1 (Germany), in accordance with ISO 11357-4:2014 (Plastics--Differential scanning calorimetry (DSC)--Part 4: Determination of specific heat capacity). As a comparison standard for determining thermal conductivity, a standard sample, sapphire, was used in the work. The heat capacity was determined on samples 5 mm in diameter, weighing 24-25 mg, in a protective argon atmosphere. Three-point tensile, bending, and compression tests at room temperature were carried out on a Zwick/Roell Z020 universal tensile testing machine (Ulm, Germany) using a high-precision MultiXtens strain measurement system. Flexural tests were carried out in accordance with ISO 178:2019 (Plastics--Determination of flexural properties), on 80 mm \(\times\) 10 mm \(\times\) 4 mm specimens. The sample was loaded until failure at an active grip travel speed of 2 mm/min. Tensile tests were performed in accordance with ISO 527-2:2012 (Plastics--Determination of tensile properties--Part 2: Test conditions for molding and extrusion plastics). Samples of type 5A were used; the strain rate was 2 mm/min.