This blog post represents the second installment in a series of posts on thermal analysis techniques for polymers. In part 1 we discussed differential thermal analysis, thermomechanical analysis, and dynamic mechanical analysis.
In part 2 our focus will be differential scanning calorimetry, thermogravimetric analysis, and evolved gas analysis. Once again we will discuss in general how the tests are performed and what types of thermal properties can be determined from the data that is generated.
Image Source DSC (Differential Scanning Calorimetry)
DSC stands for differential calorimetry, a method where the heat flux to and from a specimen of the material and a reference material is measured as a function of temperature. This is performed while the specimen is either cooled, heated, or held at a constant temperature.
There is a long list of thermal properties that can be measured using DSC, including:
- specific heat capacity
- enthalpy changes
- enthalpy of conversion
- enthalpy of melting
- chemical reactions such as polymerization
DSC can be used to gain a better understanding of polymer characteristics such as amorphous and crystalline behavior, the curing process, and transitions that occur as a function of temperature. It can be used to detect melting points, glass transition temperature, and phase changes.
TGA (Thermogravimetric Analysis)
TGA stands for thermogravimetric analysis, and it is used to monitor the mass (and weight) of a sample of material as a function of temperature in a controlled atmosphere. A sample pan supported by a precision balance is placed in a furnace and either subject to a programmed heating or cooling cycle.
By measuring mass as a function of temperature, it allows for investigation of temperatures that are used to characterize changes in mass, such as a mass loss or mass gain curve. It is used to study, among other things:
- vaporization
- sublimation
- thermal decomposition
- oxidation
- composition.
Data from TGA can aid in studying the loss of plasticizer, pyrolysis, loss of solvent, etc.
EGA (Evolved Gas Analysis)
EGA stands for evolved gas analysis, the name for a family of techniques used to study the gaseous volatile products that can be evolved from a material specimen as a function of temperature. The main techniques used in EGA are mass spectrometry and infrared spectrometry. EGA is often used with TGA instruments because the TGA effects can involve mass loss. It can used to study some of the same properties, such as vaporization, sublimation, and thermal decomposition.
Conclusion
The behavior of polymers as a function of temperature can be vital to the proper choice of a polymer for an application. In order to understand the thermal properties involved, it helps to have a solid understanding of the techniques used to obtain those properties.
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