*3.5. Testing*

The tensile test of nanocomposite series was conducted on the cured samples to study the tensile modulus, strength, and elongation properties of CNF-filled epoxy composites. The tensile test was conducted as per ASTM D3039 standard test, with specimen dimension of 5 cm gauge length × 1 cm width × 0.3 cm thick. The tensile test was conducted using an MTS UTM Tensile Tester (Model LPS 304—424708 series) with a crosshead speed of 1 mm/min and 1kN load cell. A mean value of tensile property of three specimens was selected and considered for analysis.

Barrier properties of nanocomposites was studied by a water immersion test method, as per ASTM D570-98 (2005) test procedure at 25 ◦C. Three test specimens, each of dimension 3 cm × 3 cm × 0.3 cm, were chosen for this study. In order to eliminate surface or subsurface entrapped moisture and retain actual solid mass in the specimen, test samples were dried at 60 ◦C for 4 h using an oven. During the 4 h drying, samples were taken out of the oven at an interval of 1 h and immediately transferred into the airtight desiccator. The RT-cooled sample was weighed and ensured that the mass loss remained constant until the 4 h heating cycle.

The actual solid mass sample was then immediately taken out of the desiccator and fully immersed in a distilled water medium which was placed in a temperature-controlled water bath set-up. The bath temperature was constantly maintained at 25 ◦C for entire duration of the water immersion test. The water soaked specimen was taken from the water bath at di fferent time intervals and wiped using a paper towel to eliminate surface water. The sample was then weighed in an electronic balance and then immediately transferred back into the water bath set-up. This weighing procedure was repeated until

the water soaked sample showed no or negligible increase in the water mass uptake (i.e., equilibrium water uptake content, *W*e). The *W*e was measured as per Equation (1)

$$\mathcal{W}\_t = \frac{\left(\mathcal{W}\_t - \mathcal{W}\_i\right)}{\left(\mathcal{W}\_i\right)} \times 100\tag{1}$$

where *Wi* and *Wt* are initial dry solid mass of the test specimen and the water mass uptake of soaked sample at time *t* of testing was done respectively. The barrier property was examined by selecting the mean test specimen water uptake result.
