*2.2. Measurements*

The moving die rheometer (Monsanto, MDR2000P, St. Louis, MO, USA) was used to determine the curing characteristics of NR compounds. About 5 g of rubber compound was inserted into the geometry of two parallel rotating disks at 150 ◦C at a frequency of 100 rpm. After processing was completed, the cure curve with many characteristics such as max. torque (MH), min. torque (ML), scorch time (t2), and 90% cure time (t90) were acquired.

In order to prepare the samples for tensile testing, a sheet of about 2 mm thickness was vulcanized in a molding test press (Gotech, GT7014H, Taichung, Taiwan) at 150 ◦C and a 40 kgf/cm2 pressure for a respective cure time, t90, which was estimated from the MDR 2000P measurement [42].

The tensile test was performed using an Instron universal testing machine according to ASTM D412-93 at room temperature (~25 ◦C). Tensile strengths and elongations at break were estimated from stress-strain curves and averaged values from five-time rerun measurements for each sample were obtained [34]. The Shore A hardness of the samples was evaluated following the ISO 7619-1:2010. Thermogravimetric analysis (TGA) was performed with a TGA Q50 (TA Instruments, New Castle, DE, USA) according to the ASTM D3850-94 method. Approximately 10–20 mg of vulcanized samples were loaded onto an open platinum pan, and then heated from 25 to 600 ◦C under a nitrogen environment at a fixed heating rate of 10 ◦C/min. The fracture surfaces of the fabricated nanocomposites were examined with a scanning electron microscope (SEM) (SEM JEOL 5510, JEOL, Tokyo, Japan) at 10 kV accelerating voltage.

The Mooney-Rilvin equation was used to determine the crosslinking density of the vulcanates based on the following stress-strain behavior [42]:

$$
\sigma = 2(\lambda - \frac{1}{\lambda^2})(C\_1 + \frac{C\_2}{\lambda})^2
$$

where σ, λ, *C*1, and *C*<sup>2</sup> are the tensile stress, the strain, and constants, respectively. The *C*<sup>1</sup> and *C*<sup>2</sup> constants were determined from the slope and intercept of the curve of <sup>σ</sup>/(<sup>λ</sup> <sup>−</sup> <sup>λ</sup>−2) versus 1/λ. Finally, the crosslinking density was obtained from the following equation:

$$\mathcal{ZC}\_1 = \rho \mathbf{k} \mathbf{T}$$

where ρ is the cross-linking density, k is the Boltzmann constant, and T is the absolute temperature.
