Thermogravimetric analysis measurement modes

Dynamic mechanical anlaysis (DMA) measurements were done on a Rheometrics RDS-7700 rheometer in torsional rectangular geometry mode using 60 x 12 x 3 mm samples at 0.05% strain and 1 Hz. Differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and thermogravimetric analysis (TGA) were performed on a Perkin-Elmer 7000 thermal analysis system. 

The thermal stability of polymers can be tested by thermogravimetric analysis (TGA). In this method, a sample of a few milligrams is deposited in a scale pan mounted on a furnace. TGA measurements can be done in isothermal mode by maintaining a certain temperature for a fixed period of time or in temperature cycling mode. Most often the data are obtained with a constant... 

In this chapter we present background principles of thermogravimetric analysis and the various measurement modes issues associated with and recommendations for calibration measurement and analysis methods for characterizing polymeric materials, including recommendations for how to perform a TGA experiment and kinetics. At the end of the chapter we present selected applications of actual industrial problems where TGA has been instrumental in their solution. 

Thermogravimetric analysis provides a quantitative measurement of the mass change, but does not indicate the nature of the material lost. Hence, it is often used in a combined manner with evolved gas analysis (EGA) measurements on the same sample. EGA determines the specific nature of the changes in the gas phase and may be done in a qualitative or quantitative manner. There are several modes of operation. Gas samples can be trapped and analyzed periodically either during or at the end of the experiment. More common and more useful is to monitor the atmosphere and correlate its chemical nature with the observed mass change in a near-simultaneous mode, with negligible delay between mass loss in the TGA and gas detection by EGA. 

Remark.- We see that vaeancies are intermediate components from the point of view of the global reaction. If the speeds of both processes are very different, as long as the contributions of both processes are notable, vacancy concentration varies with time and thus the pseudo-steady state test is not satisfied. It is only when one contribution becomes negligible that the system could possibly be in pseudo-steady state. The test will then give two zones of a pseudo-steady state mode but with two different ratios between calorimetric and Differential Thermogravimetric Analysis (DTAG) measurements, one for each zone. 

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