Physical Processes - Isoconversional Kinetics of Thermally Stimulated Processes - page 86

Fig. 3.21 As glass ages,
its enthalpy lowers and its
mobility slows down so that
on reheating the enthalpy
overshoot becomes larger and
shifts to higher temperature.
T p denotes the position of the
overshoot peak
measured on heating. The size of the peak is proportional to the enthalpy lost on
aging. The effect is illustrated in Fig. 3.22 [ 63 ]. Both peak temperature and recov-
ered enthalpy increase with aging time, t a , until they reach ultimate values, which
correspond to completely relaxed glass (point D in Fig. 3.21 ). The magnitude of the
ultimate values depends on chosen T a .
Fig. 3.22 DSC curves of poly(cyanobiphenyl ethylacrylate) heated at 5 ﾰC min− 1 after aging at
64 °C for 34, 64, 305, 725, and 3963 min ( solid lines in order of increasing the peak size). The
dash line represents the curve for unaged sample. (Reproduced from Tanaka and Yamamoto [ 63 ]
with permission of Elsevier)