Eclectic Techniques Measure Thermal Properties

Thermal analysis is the broad category of at least 20 techniques that measure some fundamental property of matter as a result of adding heat. For example, dilatometry measures volume changes upon heating, thermomechanical analysis quantifies the change in dimension of a sample as a function of temperature, and thermo-optical analysis detects changes in optical properties on heating or cooling.

This discussion applies mostly to two techniques, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), although many of the ideas presented here apply to other types of thermal analysis. DSC and the related micro-DSC measure the amount of heat required to change the temperature of a sample. DSC is most often used with materials that undergo phase changes.

Homogeneous or nonhomogeneous materials that melt or freeze, or that undergo transformation from one solid form to another, are excellent candidates for DSC. Notable examples include the glass transition temperature of polymers and the interconversion of crystalline polymorphs in the pharmaceutical industry. Approximately 60 percent of thermal analyses involve DSC.

TGA is often used to quantify residual solvent or moisture content of a sample (for example, in foods and pharmaceuticals). A related technique, evolved gas analysis, analyzes gas decomposition products.


From the perspective of Kenneth Aniunoh, Ph.D., senior product specialist at Shimadzu Scientific Instruments (Columbia, MD), thermal analysis is trending toward user-friendly software, smaller and more compact instruments, availability of auto-samplers, and greater value. “The same is true for many other laboratory instrument types,” says Aniunoh. “Bench space is at a premium, and overly complicated software can be a real detriment to productivity.”

Simplification without sacrificing features is a trend observable in most lab instruments. Thermal analyzers are no exception. “Thermal analysis used to require an operator with a Ph.D. in calorimetry or rheology,” notes Kevin Menard, global product manager for thermal, elemental, and hyphenated analysis at PerkinElmer (Shelton, CT). “Now it is a more general-purpose tool. Most of the activity is no longer directed at new instrumentation, but at applications and the development of standardized methods.”

For instrument manufacturers, this means producing systems that are more accessible to technicians with a B.S. degree or even just a high school diploma. Vendors must provide a level of support based on users’ expertise and applications.

This is not as straightforward as it sounds, because many industries test the same types of samples. Polymers, which are targets for up to 70 percent of all thermal analyses, are tested not just at the raw plastics processing plant, but in nearly every manufacturing industry, especially packaging.

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