*2.2. Characterization and Testing of Epoxy Polymer and Nanocomposites*

Both the pristine glassy epoxy polymer and the epoxy-clay nanocomposites were characterized for their mechanical properties (tensile measurements), thermomechanical properties (Dynamic Mechanical Analysis, DMA), thermal stability (Thermogravimetric Analysis, TGA), and barrier properties (O2 permeability measurements). X-ray diffraction (XRD) was also applied in order to determine the degree of intercalation/exfoliation of clay nanoplatelets within the epoxy polymer. The dispersion of clay nanolayers within the polymer matrix was investigated by means of High Resolution Transmission Electron Microscopy (HRTEM).

XRD measurements were performed on a Siemens D-500 (Siemens AG, Karlsruhe, Germany) type automated diffractometer, with Cu(Kα) λ = 1.5418 Å radiation, in the range 2◦–10◦ 2θ and at a scan rate of 1◦/min. HRTEM measurements were performed on a JEOL 2011 high resolution transmission electron microscope (Jeol, Peabody, MA, USA) with a LaB6 filament (TED PELLA Inc., Redding, CA, USA) and an accelerating voltage of 200 kV, a point resolution of 0.23 nm, and a spherical aberration coefficient of *C*s = 1 mm. The TEM samples were prepared by supporting thin sections (80–100 nm) of the nanocomposite samples onto a lacy carbon film supported on a 3 mm diameter, 300 mesh copper grid. The specimens were further coated with a carbon layer in order to enhance conductivity and avoid destruction of the epoxy polymer.

The mechanical properties of the samples were measured with an Instron 3344 dynamometer (Instron, Norwood, MA, USA) according to the Standard Method (ASTM D638) [21], with a stress rate of 5 mm/min. The specimens had a dogbone shape and dimensions of 40 mm × 5 mm × 2 mm and were prepared in rubber molds by curing of the epoxy/amine mixture, as described above. The thermomechanical properties were measured using a Perkin Elmer Diamond DMA analyser (Perkin Elmer, Waltham, MA, USA). The bending method was used with a frequency of 1 Hz in a temperature range 25–150 ◦C. The heating rate was 2 ◦C/min and the applied stress was 4 N. The samples had a rectangular shape with dimensions of 50 mm × 13 mm × 2 mm, also prepared in rubber molds. Thermogravimetric (TGA) experiments on the epoxy nanocomposites were performed using an SDT2956 (TA instruments, New Castle, DE, USA) thermobalance under Ar inert gas flow (100 cm3/min) and at a constant heating rate of 10 ◦C/min in the temperature range of 25–900 ◦C.

Oxygen permeability measurements were performed on an Analyzer M8001 (Systech Illinois, Johnsburg, IL, USA) according to the Standard Method (ASTM D3985) [22]. The oxygen transmission rate (OTR, cc/m2 day) and permeability (OTR specimen thickness, cc mm/m2 day) were measured at a constant temperature of 23 ◦C and zero relative humidity (0% RH). The specimens tested were the pristine epoxy polymer disks and the epoxy-clay nanocomposite disks, with an average thickness of 2 mm.
