Generally, the detection of TgÕs by TMA appears differently for thermoset
versus thermoplastic materials. For thermoplastic materials expansion is detected
prior to the Tg and penetration into the sample at the Tg, whereas for thermoset
materials expansion is detected prior to and after the Tg, with penetration at the
Tg. These same types of curve characteristics are seen in mTMA also. Figures 1a
and 1b illustrate these two types of characteristic Tg detection on polystyrene and
90 minute epoxy respectively. The figures show plots of probe deflection versus
temperature. A positively sloping curve indicates that expansion of the
probe/sample system is occurring while a negative slope indicates penetration due
to softening of the surface.