2.3. Viscosity measurements
The viscosity of the starch/gelatin solutions was measured at
room temperature (23 ◦C) using a Brookfield digital viscometer
(Model DV-II+ PRO with LV S6-3 spindle) operating at 30 rpm for all
samples. The viscometer spindle was immersed into the solution
for about 3 min to achieve thermal equilibrium between the solution
and spindle with continued shearing. Five viscosity readings
were recorded for each solution, and average values were taken.
Tests were run in triplicate.
2.4. Transparency measurements
A UV (WFZ UV-3802) spectrum was used to measure the
transparency of the different solutions, which were placed in
a 10 mm
×
10 mm square sample container for measurement. A
wavelength of 206 nm was used to indicate transparency in this
work. The transparency of different films was also measured at a
wavelength of 206 nm and divided by thickness and presented as
%/mm.
2.5. Mechanical properties
Dumbbell-shaped specimens (gap 50 mm, width 1 mm) were
cut from cast films then equilibrated at 56% RH (controlled by NaBr
solution) for 72 h before testing. The tensile properties of specimens
were measured in accordance with ASTM D638 using an Instron
mechanical testing apparatus (Model 3366). Young’s modulus, tensile
strength and elongation were measured at a crosshead speed
of 10 mm/min. Each test trial per film consisted of seven replicate
measurements.