2.13. Tensile Test

The tensile properties of the films were measured with a universal testing device (Instron 5544, USA) at controlled environmental conditions (relative humidity of 50% and temperature of 23 °C). Prior to measurement, films were cut into strips at a length of 70 mm and a width of 5 mm, and the average thickness of each strip was measured at three random positions with a thickness gauge (FT3 Precision Thickness Gauge, Hanatek Instruments, U.K.). Five samples of each film were measured with a 2 kN force sensor, at a gauge length of 40 mm and a strain speed of 5 mm min^–1 until a break occurred.