Thermal Analysis of Polymers. Part 4: TGA, TMA and DMA of Thermosets - METTLER TOLEDO

Thermal Analysis of Polymers. Part 4: TGA, TMA and DMA of Thermosets

In Part 3 (UserCom 33) of this series, we described the most important effects that can be investigated by DSC in the field of thermosets [1]. This article focuses on the application of TGA, TMA and DMA and shows how additional information can be obtained using these techniques. In particular, it discusses decomposition, expansion, the glass transition and its frequency dependence.

Figure 1: TGA/DSC 1 curves of KU600 epoxy powder measured from 30 to 700 °C at a heating rate of 20 K/min. The TGA curve (red) measures the loss of mass and the DSC curve (black) provides information about endothermic and exothermic effects.

 

Thermogravimetric Analysis (TGA)

Thermogravimetric analysis is a technique that measures the mass of a sample while it is heated, cooled or held at constant temperature in a defined atmosphere. It is mainly used for the quantitative and compositional analysis of products [2].

Figure 1 (middle curve, red) shows the decomposition curve of KU600 epoxy resin measured by TGA. The finely powdered sample was heated from 30 to 700 °C at a heating rate of 20 K/min in a 30-μL alumina crucible without a lid using a purge gas flow rate of 50 mL/min. The purge gas was switched from nitrogen to air at 600 °C.

The polymer content of the material is determined from the loss of mass due to pyrolysis up to about 500 °C. The purpose of the switching the purge gas to air at 600 °C was to oxidize the carbon black formed during the pyrolysis reaction.

The final residue consisted of inorganic fillers such as silicates or oxides. The first derivative of the TGA curve is known as the DTG curve and is a measure of the decomposition rate. Both the DTG curve (blue) and the DSC curve (black) are usually plotted together with the TGA curve. The DSC curve is recorded simultaneously with the TGA measurement and often provides valuable additional information about the sample.

In this example, we can identify the glass transition at about 60 °C and the curing reaction between 120 and 240 °C. The DSC curve also yields information about the decomposition reaction and the combustion process.

 

Thermomechanical Analysis (TMA)

Thermomechanical analysis (TMA) is used to measure the dimensional changes of a sample while it is heated or cooled in a defined atmosphere. The most important analyses are the determination of the coefficient of thermal expansion (CTE, expansion coefficient), the glass transition, and the softening of materials...



Download the full text of this article below.



Conclusions

This article and the previous article in UserCom 33 [1] discussed the different possibilities available for characterizing a thermoset (KU600) using the familiar DSC, TGA, TMA, and DMA techniques. The various methods yield consistent results.

The main effects investigated were the glass transition, the curing reaction, expansion, decomposition. Furthermore, the application of model free kinetics was discussed and the frequency dependence of the glass transition shown using DMA measurements. Other thermosets show similar effects.

A particular effect can often be measured by different thermal analysis techniques. The results obtained from one technique often provide complementary information and confirm the results from another technique. Ideally, a material is first analyzed by TGA, then by DSC and TMA, and finally by DMA.


Thermal Analysis of Polymers. Part 4: TGA, TMA, and DMA of Thermosets | Thermal Analysis Application No. UC341 | Application published in METTLER TOLEDO Thermal Analysis UserCom 34

KU600 DSC TGA DTGFigure 1: TGA/DSC 1 curves of KU600 epoxy powder measured from 30 to 700 °C at a heating rate of 20 K/min. The TGA curve (red) measures the loss of mass and the DSC curve (black) provides information about endothermic and exothermic effects.

In Part 3 (UserCom 33) of this series, we described the most important effects that can be investigated by DSC in the field of thermosets [1]. This article focuses on the application of TGA, TMA and DMA and shows how additional information can be obtained using these techniques. In particular, it discusses decomposition, expansion, the glass transition and its frequency dependence.


Thermogravimetric analysis (TGA)

Thermogravimetric analysis is a technique that measures the mass of a sample while it is heated, cooled or held at constant temperature in a defined atmosphere. It is mainly used for the quantitative and compositional analysis of products [2].

Figure 1 (middle curve, red) shows the decomposition curve of KU600 epoxy resin measured by TGA. The finely powdered sample was heated from 30 to 700 °C at a heating rate of 20 K/min in a 30-μL alumina crucible without a lid using a purge gas flow rate of 50 mL/min. The purge gas was switched from nitrogen to air at 600 °C.

The polymer content of the material is determined from the loss of mass due to pyrolysis up to about 500 °C. The purpose of the switching the purge gas to air at 600 °C was to oxidize the carbon black formed during the pyrolysis reaction.

The final residue consisted of inorganic fillers such as silicates or oxides. The first derivative of the TGA curve is known as the DTG curve and is a measure of the decomposition rate. Both the DTG curve (blue) and the DSC curve (black) are usually plotted together with the TGA curve. The DSC curve is recorded simultaneously with the TGA measurement and often provides valuable additional information about the sample.

In this example, we can identify the glass transition at about 60 °C and the curing reaction between 120 and 240 °C. The DSC curve also yields information about the decomposition reaction and the combustion process.


Thermomechanical analysis (TMA)

Thermomechanical analysis (TMA) is used to measure the dimensional changes of a sample while it is heated or cooled in a defined atmosphere. The most important analyses are the determination of the coefficient of thermal expansion (CTE, expansion coefficient), the glass transition, and the softening of materials...



Download the full text of this article below.



Conclusions

This article and the previous article in UserCom 33 [1] discussed the different possibilities available for characterizing a thermoset (KU600) using the familiar DSC, TGA, TMA, and DMA techniques. The various methods yield consistent results.

The main effects investigated were the glass transition, the curing reaction, expansion, decomposition. Furthermore, the application of model free kinetics was discussed and the frequency dependence of the glass transition shown using DMA measurements. Other thermosets show similar effects.

A particular effect can often be measured by different thermal analysis techniques. The results obtained from one technique often provide complementary information and confirm the results from another technique. Ideally, a material is first analyzed by TGA, then by DSC and TMA, and finally by DMA.



Thermal Analysis of Polymers. Part 4: TGA, TMA, and DMA of Thermosets | Thermal Analysis Application No. UC341 | Application published in METTLER TOLEDO Thermal Analysis UserCom 34