Analytical Chemistry

The second loss of 40% of the polymer is due to cyclization, loss of tars and other products.

Note: The identity of the polymer and of the products could be checked by other analyses, for

example, spectrometry.

(4) The techniques of Differential Thermal Analysis (DTA) and of Differential Scanning Calorimetry
(DSC) both investigate the heat energy changes during the heating or cooling process. There are many
different apparati, and their construction and sensitivities overlap considerably. The following is a guide
to their main similarities and differences;

DTA DSC

Measures exo- and endothermic events. Measures exo- and endothermic events.

Measures temperatures of events. Measures temperatures of events.

Shows effects of atmosphere, sample history, purity, etc. Shows effects of atmosphere, sample history, purity, etc.

Measures sample temperature directly. Measures temperature of sample container.

Calorimetric sensitivity may depend on sample. Calorimetric sensitivity independent of sample.

Better temperature resolution. Better for calorimetric measurements.

(5) The calorimetric sensitivity is found from the calibration with indium:

Fusion of 5.89 mg of indium: 5.89 × 28.45 = 167.56 mJ

Sensitivity is: 167.57/40.0 = 4.189 mJ/cm^2

Therefore, for PET, Peak = 116.3 × 4.189 = 487.2 mJ

So, since mass was 9.94 mg: 487.2/9.94 = 49.0 mJ/mg

or ∆Hfus = 49.0 J/g

Since the pure, crystalline PET had a ∆Hfus of 117.57 J/g, this sample is about 100 ×

49.0/ 117.57 = 41.7% crystalline.