Instant Notes: Analytical Chemistry

Applications The expansion of a plastic component may be studied by TMA.Figure 2shows
that below 112°C, the coefficient of expansion is about one third of the value
above this temperature. This measures the glass transition temperature, Tg, as
112 °C. Note that the dimension of the sample is very small and the dimensional
change even smaller.
Similar techniques can be used to study softening and penetration, swelling
by solvent and sintering.
The DMA of a plastic component is illustrated in Figure 3. For many plastics,
their structure causes characteristic low temperature transitions. Solvents or

318 Section G – Thermal methods

a = 50 x 10–6

a = 150 x 10–6

Tg = 112°C

30

20

10

0

0 50 100 150

Temperature (°C)

200 250

Dimension (

mm)

Fig. 2. TMA curve for printed circuit board.

5 4 3 2 1 0

400

300

200

100

0

–150 –100 –50 0 50 100

Temperature (°C)

–124.0

–23.00

–13.14

–2.850

[ ]

E (MPa)

[ ]

E (GPa)

Fig. 3. DMA traces of latex rubber film showing a low-temperature transition at − 124 °C. The glass transition is at − 13 °C.