2.3. Physicomechanical properties of NRL films
The methods used for evaluating mechanical properties were based on the guideline of the American Society for Testing Materials, ASTM. The film specimens were cut into rectangular shape and determined the mechanical properties using Instron testing machine (model 5569; Instron Corporation, USA) with a 500 N loaded cell. The mechanical studies of films were monitored by the tensile strength which modified from the ASTM D412 in terms of Young’s modulus, UTS, elongation at break [7], and the adhesiveness in term of tack adhesion which modified from the ASTM D6195 [8].
Tensile strength was determined following the method which modified from the ASTM D412 [7]. The size of film specimens was 10
2
which the gauge length of tested area was 10 mm. The crosshead speed was controlled at 10 mm/min. The Young’s modulus, which is the manifestation of stiffness of a material, is calculated from the initial slope of the stress-strain plot within the range of elastic limit of stretching. The UTS is defined as either a distinct maximum or a region of strong curvature approaching zero-slope in the stress-strain curve. The elongation at break is determined by removing the fractured specimen from the grips, fitting the broken ends together and measuring the distance between gages makes. These mechanical properties were calculated by Equations 1-3.
Strain Stress
modulus sYoung'