Tensile strength.
Tensile strength was determined in term of Young’s modulus, ultimate tensile strength
(UTS), and elongation at break using an Instron testing machine (model 5569, Instron Corporation, USA.)
with a 500N loaded cell following the method modified from the ASTM D412 [7]. Films were cut into
the rectangular specimens of 10 u 30 mm2
. The gauge length was set at 10 mm and the cross-head speed
was controlled at 10 mm/min. The Young’s modulus, which is the manifestation of stiffness of a material,
was calculated from the initial slope of the stress-strain plot within the range of elastic limit of stretching.
The UTS was expressed as the maximum force at break divided by the initial cross-sectional area of the
film strip, and the elongation at break as a percentage of the original length. These tensile values were
calculated by equation 1-3, respectively.