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Different thermal analysis methods have become a popular route for determining how different polymers behave under different temperature environments. Some polymers can be used in high-temperature environments, or in environments where the temperature is likely to fluctuate, so understanding this behavior is utmost importance for polymer applications, and some applications directly rely on these thermal properties. In this article, we look at the different types of thermal analysis methods used on different polymer classes.
What is a Thermal Analysis?
Thermal analysis, in its most basic sense, is the study of a material’s property with changing temperature. However, there is not one set thermal analysis method, and much like elemental analysis, there are many different techniques that can be used to build up a big picture of how a material behaves at different temperatures. Each class of material will use a different set of techniques, but overall, thermal analysis techniques commonly encompass differential thermal analysis (DTA), single differential thermal analysis (SDTA), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), thermo-optical analysis (TOA), thermomechanical analysis, dielectric analysis (DEA) and thermochemiluminescence (TCL). No single technique can measure every single thermal property of interest (although some can measure a lot), so a combination of techniques is always required to understand how the material will behave. For polymers, DSC, TGA, DMA, and DTA are the most common thermal analysis methods.
How Thermal Analysis Can Be Used for Polymers
There are many different polymers that change under temperature, and in respect to their effectiveness in different environments, these properties need to be studied. Overall, polymers are one of the most widely studied materials using thermal analysis methods. Each type of polymer has different requirements, different heating mechanisms and different properties that are important for that specific class, therefore, a tailored approach is required. Here, we look at how thermal analysis methods are used for a few different types of polymer, namely thermoplastics, thermosetting polymers, and elastomers—all of which have very different priorities when it comes to property requirements.
Thermoplastics are a class of polymers that become plastic upon heating but harden when cooled, therefore understanding the thermal profile is important. A wide range of techniques are used on thermoplastics to deduce their properties and often include DSC, TGA, TMA, DMA, and DEA. The combination of these techniques enables the scientist to deduce the glass transition temperature of the polymer—which in turn also provides the specific heat capacity, coefficient of thermal expansion, mechanical modulus and dielectric constant—as well as the degree of crystallinity of the thermoplastic, the ability of the thermoplastic to undergo recrystallization, the heating-cooling-heating profile of the thermoplastic, how different cooling rates influence the properties of the thermoplastic, and the oxidative stability, melting and cold crystallization properties, the decomposition rate and the thermal history of the thermoplastic sample in question.
A thermosetting polymer is a polymer which irreversibly hardens after being cured by heat. Unlike thermoplastics, which are reversible, the hardening is permanent due cross-linking of the polymer chains. Given the versatility of the techniques, DSC, TGA, TMA, DMA, and DEA can again be used to determine the thermal properties of thermoset polymers. For thermoset polymers, these combined techniques can deduce the glass transition temperature (and associated sub-properties that contribute to the value), the frequency dependence of the glass transition, the kinetics of the curing reaction, whether the curing reaction is isothermal or dynamic, the softening temperature of a thin thermosetting polymer coating and for determining the thermal history, thermal decomposition, thermal expansion, Young’s modulus of the thermosetting polymer.
Elastomers are a class of polymeric materials that have elastic properties, i.e. they are said to be viscoelastic, and stretch when they are pulled. The properties of elastomers are vastly different to those of thermoplastic and thermosetting polymers, but DSC, TGA, TMA, and DMA are generally used again because they can measure a vast range of thermal properties. For elastomers, these techniques are employed to measure the glass transition temperature, Young’s modulus, master curves and damping behavior of an elastomer, as well as for determining the frequency dependence of the glass transition, the creep behavior and recovery (including viscoelastic relaxation and viscous flow properties),the swelling behaviour, and the effects that filler materials have on the mechanical properties and vulcanization of an elastomer.
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