In this blog post, we are going to start a discussion about the most common thermal analysis techniques used to investigate the properties of polymers. In part 1 of this series, our focus will be on:
- differential thermal analysis
- thermomechanical analysis; and
- dynamic mechanical analysis
This discussion will include how these tests are performed and what kind of properties can be determined from the resulting data.
Need for Thermal Analysis of Polymers
The mechanical behavior of polymers is far more dependent on temperature than that of metals. In order to select the optimal polymer for an application, it is important to investigate the thermomechanical properties of the polymers in question. DTA, TMA, and DMA are three common thermal analysis techniques used to characterize the behavior of polymers as a function of temperature and gain a more thorough understanding of their suitability for applications.
DTA (Differential Thermal Analysis)
DTA stands for Differential Thermal Analysis, and its objective is to obtain an accurate measure of temperature difference between a sample and an inert reference material, measured as a function of temperature. Both the sample and the reference material are made to undergo the same thermal cycling and the readings are taken over time. It is used to obtain measurements of solid-solid transitions, polymorphism, oxidative degeneration, and oxidative stability. While not ideally suited for such measurements, it can also be used to measure specific heat capacity, enthalpy changes, melting point, temperature stability, chemical reactions, glass transition temperature, and thermal decomposition (among other properties).
TMA (Thermomechanical Analysis)
TMA stands for Thermomechanical Analysis and its goal is to measure the dimensional changes of a polymer as a function of temperature. In this type of test, a specimen of the material is subjected to a force (either constant, increasing, or modulated) using the smallest possible load and any changes in dimensions are measured. It can be used to detect more than just changes in shape. TMA can be used to measure the coefficient of thermal expansion and changes in it and determine the temperatures that characterize a particular thermal effect such as the glass transition temperature, Tg. It can also be used to detect the softening of a material, study viscoelastic behavior, measure elastic modulus, detect melting point, and determine melting fractions.
DMA (Dynamic Mechanical Analysis)
DMA stands for Dynamic Mechanical Analysis and it is performed by subjecting a specimen of the material to a sinusoidal mechanical stress. From that, the force amplitude, deformation amplitude, and phase shift can be determined as a function of either temperature or frequency. DMA is primarily used to investigate the glass transition temperature, shear modulus, elastic modulus, mechanical damping, and viscoelastic behavior.
Importance of Thermal Properties
When selecting a polymer for an application, it is important to remember that the thermal and mechanical behavior of a polymer are closely related. To choose the optimal material, remember to take into account the thermal properties as well as the mechanical properties.