where Ws is the dry insoluble sample mass (g),
Wi is the initial mass of the sample (g), and
Wo is the mass of the metal cage.
TGA tests of the surface region of the samples were conducted (Netzsch
model TG 209F1 Libra) under a nitrogen atmosphere at a flow rate of 30
mL/min and heating rate of 10 °C/min, from 30 to 800 °C. The inflection
point of the thermogravimetric curve was considered as the onset of
decomposition.
DSC tests were conducted using an Indian calibrated Netzsch model DSC
404 F1 Pegasus, which was coupled to a computerized analysis system as
per the ASTM D3417 standard testing method [17]. Samples were
collected from the surface region for each testing condition, weighing
between 0.9 and 1.1 mg, and placed in aluminum crucibles. The samples
were subjected to a double heating/cooling cycle ranging from -100 °C to
300 °C at a heating rate of 10 °C/min under a nitrogen atmosphere at a
flow rate of 20 mL/min. Under these conditions, it was possible to
calculate the degree of crystallinity of PS before and after radiation
exposure using Equation 4.