The Ôfree
volumeÕ is the volume unoccupied by the ``solid matter''
of the molecules and represents the volume available for
their free movements (Flink, 1983). Accelerated changes
in the above properties as a function of temperature are
the basis for detecting the glass transition temperature.
The changes continue over a relatively narrow band of
temperatures, therefore, onset and termination Tg values
are observed. Some of the analytical methods to determine
Tg are dierential scanning calorimetry (DSC),
dierential thermal analysis (DTA) and thermal mechanical
analysis (TMA). The former two methods detect
changes in Cp, while the third detects changes in the
elastic modulus.