Thermal analysis has been a method of characterization for many years, with its usefulness widely recognized within the scientific community. There are many methods used across industry, including differential scanning calorimetry, thermogravimetric and thermomechanical analysis.
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Why Thermal Analysis?
Studying polymers is the most widespread use of thermal analysis. It is used to measure the physical properties of materials as well as their thermal and mechanical history. This is used to estimate polymer lifetimes within different environments, helping keep polymers reliable and sustainable.
These histories can also be used to aid in designing and characterizing processes used in the manufacture of polymers. This has led to thermal analysis instruments being used in laboratories for all industries where plastics and polymeric materials are used.
This makes thermal analysis one of the staple quality control and research tools within the manufacture of polymeric materials. Manufacturers are constantly trying to create complete systems in order to allow a wide range of analysis; this in turn creates a need for increased efficiency, miniaturization, and automation within polymeric material manufacture.
Methods of Thermal Analysis
Differential Scanning Calorimetry
The most popular method to characterize polymeric materials is Differential Scanning Calorimetry (DSC). This method involves heating, cooling, or keeping a material at a constant temperature in order to measure its energy output. This is called enthalpy as a function of temperature.
As DSC is widely used, it is a very cost-effective method of analysis, with calorimeters and other instruments being relatively inexpensive. However, DSC does have some limitations. DSC is not easily repeatable with the same material over different laboratories, and it also requires a reduced sample size when determining a material's properties.
Another method of thermal analysis is Thermogravimetric Analysis (TGA). TGA measures the mass of a sample of polymeric materials as a function of temperature or time whilst it undergoes a controlled heating program.
Thermogravimetry can be used to simulate roasting temperatures and other conditions and is used to produce a small sample of material to be used for characterization or chemical analysis. TGA can be used with DSC to identify endothermic and exothermic reaction temperatures. It can also be used to measure a material’s thermal stability, moisture, solvency, and filler content.
TGA does have some limitations, mainly that the mass loss and degradant formation are not equivalent, which impedes the ability to find indicators of the extent of degradation using TGA. This means that when TGA is used, degradation could be significantly higher than shown using this method.
Thermomechanical and Direct Mechanical Analysis
Thermomechanical and Direct Mechanical Analysis are two of the other methods used to characterize polymers. Thermomechanical analysis (TMA) measures material deformation as it is under a non-oscillatory load, meaning the pressure applied is constant, and the load displays no back-and-forth motion. TMA uses a low force range, meaning it is a safer test to conduct, and it also allows for greater alterations to the applied force.
TMA has limitations, however, as the sample needs to be reasonably flat and have parallel faces, which allow expansion. A high operating temperature range of approximately 150°C to 1,000°C causes greater cost and safety concerns due to burn risks and the energy cost to maintain these conditions.
Direct Mechanical Analysis (DMA) is similar to TMA but uses an oscillatory load and measures the polymeric material dynamic modulus and damping from the resulting deformation. DMA allows the mechanical and thermal properties of a polymeric material to be tested over a wide range of temperatures and oscillatory frequencies to give researchers and manufacturers a better understanding of a polymer.
This wide range also allows manufacturers to see how polymers perform within different environments, but DMA has drawbacks within its process as materials can only have a stiffness ranging between 1 kPa and 1,000Gpa, and modulus values obtained have been found to be less accurate than the same values obtained by conventional mechanical tests.
Research and Development
In a 2016 study in the journal Polymer International by the Society of Chemical Industry, new experimental techniques were examined to create and improve thermal analysis methods. One of these was thermal insulation, which aids in the reduction of noise within readouts from material analysis instruments. However, this additional shielding also causes concerns about measurement accuracy as heat transfer is reduced.
A solution to this found by researchers was to use a technique called thermal modulation. This uses a periodic signal rather than a continuous signal commonly used within many thermal analysis methods. The research found that the periodic signal had a better signal-to-noise ratio when compared to the steady signal, like that used within DSC.
Thermal analysis has provided some useful tools that have allowed manufacturers to innovate and adapt new and existing polymers to create better products and safer, more sustainable materials. As technology progresses, more methods and ways to improve the methods used today will arise, giving way to even more innovation.
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References and Further Reading
Battle, T., Neelameggham, N., Pistorius, C., Sanchez-Segado, S., Downey, J., Davis, B., & May, L. (Eds.). (2016). Drying, Roasting, and Calcining of Minerals. Springer International Publishing.
Cadence System Analysis. (2021). Thermal Analysis of Polymers | System Analysis Blog | Cadence. System Analysis. Retrieved February 2, 2023, from https://resources.system-analysis.cadence.com/blog/msa2021-thermal-analysis-of-polymers
eurofins; EAG Laboratories. (n.d.). Thermomechanical Analysis | TMA. EAG Laboratories. Retrieved February 3, 2023, from https://www.eag.com/techniques/phys-chem/thermomechanical-analysis-tma/
Moseson, D. E., Jordan, M. A., Shah, D. D., Corum, I. D., Alvarenga Jr., B. R., & Taylor, L. S. (2020, November 30). Application and limitations of thermogravimetric analysis to delineate the hot melt extrusion chemical stability processing window. International Journal of Pharmaceutics, 590. ScienceDirect. https://doi.org/10.1016/j.ijpharm.2020.119916
PhotoMetrics, Inc. (n.d.). Thermogravimetric Analysis (TGA) – PhotoMetrics. PhotoMetrics, Inc. Retrieved February 2, 2023, from https://photometrics.net/thermogravimetric-analysis-tga/
Prime, R. B., & Menczel, J. D. (Eds.). (2009). Thermal Analysis of Polymers: Fundamentals and Applications. Wiley.
Saruyama, Y., Tatsumi, S., & Yao, H. (2016, May 26). Recent progress in thermal analysis ofpolymers: experimentaltechniques and a new aspect of temperaturein measurement of material properties. Polymer International, 66(2), 207-212. Wiley Online Library. https://doi.org/10.1002/pi.5162
Weitzenböck, J. R. (Ed.). (2012). Adhesives in Marine Engineering. Elsevier Science.
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