Formulators Forum, July/August 2026
Posted on Wednesday, July 1, 2026
Differential Scanning Calorimetry and the Characterization of Powder Coatings
Contributed by Bob Rowles
Differential scanning calorimetry (DSC) is an analytical technique used by polymer chemists and material scientists to understand the thermodynamic behavior of materials and mixtures. When applied to powder coatings, the formulator can gain insight into:
- Relative smoothness (lower Tg generally results in smoother films)
- Physical storage Stability (low Tg can be indicative of poor storage stability)
- Presence of waxes/low melting point materials in a powder formulation
- Powder processing information
- Onset of cure
- Peak reaction temperature
- Energy released during cure
- Assess cure of field samples/customer parts (The most common application of DSC in powder coatings is the assessment of cure via Tg analysis.)
The temperature at which the segmental mobility of polymer chains changes significantly is the official definition of Tg. Alternate working definitions for this application include:
Powder Tg: The first measurable indication of particle softening
Film Tg: The first measurable indication of film softening
While not technically precise, these definitions are easier to conceptualize for powder coating applications.
Method: The temperature of a test sample is gradually increased at a precise and controlled rate (usually 20°C/min). By measuring the energy absorbed or released during this process, a formulator can determine the material’s Tg, as well as a variety of other properties.
An example recipe for a typical DSC analysis is provided here:
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Step
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Action
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Description
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1
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Data Off
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Suspends data collection for supporting steps.
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2
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Ramp 20°C / min to 0°C
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Standard starting temperature.
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3
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Isotherm for 1 minute
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Equilibrates instrument prior to temperature ramp.
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4
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Ramp 20°C / min to 100°C
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Polymer relaxation step. Ramp to a temperature above Tg but below crosslinking. Very important step for repeatability.
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5
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Isotherm for 1 minute
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Equilibrates instrument
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6
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Ramp 20°C / min to 0°C
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Return baseline temperature
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7
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Isotherm for 1 minute
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Equilibrates instrument
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8
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Data On
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Starts collecting data for primary analysis step
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9
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Ramp 20°C / min to 250°C
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Primary analysis step capturing Tg and thermodynamic data
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10
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Data Off
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Turns off data collection for supporting steps
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11
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Isotherm @ 250°C for 1 minute
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Equilibrates instrument
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12
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Ramp 20°C / min to 40°C
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Return instrument holding temperature. End of Test
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Most of the information from a powder sample is captured in Step 9.
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Powder Tg
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61.9°C
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Onset of reaction
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141.5°C
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Heat of reaction
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19.0 J/g
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Peak reaction temperature
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196°C
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Primary analysis capturing Tg and thermodynamic data. Inflection points are derived to characterize cure profile.
Film Analysis: When combining film and powder analysis, the formulator can estimate the percent cure of a given sample. The same DSC recipe listed above can be used for film measurements as well.
Percent Cure: Percent cure can be estimated using both film and powder Tg measurements with the following calculation.
Where:
Tgp = Powder Tg of test material
Tgs = Film Tg of field sample
Tgc = Film Tg of fully cured control sample (A fully cured panel in a controlled laboratory oven)
Defining Cure: The procedure listed above defines cure via instrumentation. In lieu of a DSC, cure can also be assessed by the evaluation of physical properties such as impact or solvent resistance. The same general process applies.
- Create a known control by fully curing material in a laboratory and benchmark physical properties.
- Compare the physical properties of the test sample to the known control.
These methods define cure from a crosslinking and chemical reaction perspective. However, it is equally important to keep the customer’s real-world performance expectations in mind during this analysis. Ultimately, acceptable cure is not determined solely by laboratory data, but by the minimum level of cure necessary to consistently meet the customer’s specifications for appearance, durability, adhesion, chemical resistance and overall performance. While DSC remains a highly valuable tool for evaluating cure behavior and reaction completeness, this practical, application-driven definition of cure is often the most meaningful measure of success.
Bob Rowles is the technical director - powder coatings at Cardinal Paint and Powder.