2.2.2. Membrane Mechanical Strength Measurement

Tensile strength of the selected membranes was measured before and after soaking membranes into V⁵⁺ solution for 10 days. The membranes after chemical stability testing were soaked into 2 M H₂SO₄ for one day before tensile strength measurements. The membranes were die-cut to a barbell shape using a standard ASTM D638-4 cutter. The tensile tests were conducted on a universal test machine (2000 R System, Test Resources) with a load sensitivity of 0.1 N at room temperature (RT, 21 °C) and in atmosphere (approximately 40% RH was controlled by the building air condition system and measured when testing). The strain rate used was 0.015 s⁻¹. Triplicate measurements were conducted for each membrane. Wet state membrane samples were used for AHA, AMV and CMV membranes, while dry state membrane samples were used for the rest of the membranes.

The measured tensile strength of the membrane before the chemical stability test is treated as the initial membrane mechanical strength, while the tensile strength measured after the chemical stability test is used for evaluating membrane chemical stability based on the mechanical property changes.