Tips & Tricks

Factors Influencing the DSC and TGA Measurement Results

In order to establish the origin of a failure or shortcoming, the DSC and TGA measurement results of raw material manufacturers and processors are carefully compared – not only in round-robin tests conducted by various laboratories, but also in failure analysis, especially for such areas as plastic parts.

The operators both on the supplier and customer side of course discuss their respective measurement parameters with each other, but are often surprised to find that there are still differences in the measurement plots – not to mention different interpretations of the measurement curves. 

The following table shows an overview of the great variety of criteria influencing DSC and TGA measurement results, with a description of each. 

Influential factorCriterionRecommendations/Examples
Sample preparationSamplingsampling point on the polymer mold, near/away from the gate
Sample preparationcutting with a scalpel, punching out
Sample pre-treatmenttempering at defined storage temperatures, moisture
Sample masssample weight of 10 +/-0.1 mg
Sample DensityThe mass density is defined as the ratio between mass and volume. densityespecially important for powders (bulk density)
Sample shape, surfaceflat disk for a large area of contact on the DSC sensor
DSC/TGA instrumentSensor typetype of thermocouple and sample carrier
Temperature calibrationdependent on the heating rate
Sensitivity calibrationdependent on the atmosphere, crucible and sensor type (thermocouple)
Type of purge gas (atmosphere surrounding sample)inert gas (e.g. nitrogen) or reaction gas (e.g. oxygen)
Purge gas flow20 ml/min
Protective gas flow50 ml/min nitrogen in order to avoid condensation effects in the low-temperature range
Cooling typeintracooler, liquid nitrogen, air compressor for DSC
Vacuumlowering of the boiling point of solvents, plasticizers for TGA
Drift behavior of the baselinesfor TGA/STA and DSC
Buoyancy behaviorfor TGA/STA
Measuring parametersTemperature rangefinal temperature max. 40 K over the last expected thermal effect for DSC
Heating/cooling rate10 K/min
Reheatingfor DSC measurements on polymers, a 2nd heating is required since the 1st heating also includes the thermomechanical history
Temperature/time programTM-DSC, IsothermalTests at controlled and constant temperature are called isothermal.isothermal steps instead of linear heating rate
Crucible type (shape, material, volume)crucibles with pierced lid, pressure crucibles for polycondensation, Thermal ConductivityThermal conductivity (λ with the unit W/(m•K)) describes the transport of energy – in the form of heat – through a body of mass as the result of a temperature gradient (see fig. 1). According to the second law of thermodynamics, heat always flows in the direction of the lower temperature.thermal conductivity of the crucible material, compatibility between sample and crucible material
Reference crucible for DSC/STAempty or filled with inert materials
Gas changeOxidative Induction Time, Oxidative-Induction Time (OIT) and Oxidative-Onset Temperature (OOT)Oxidative Induction Time (isothermal OIT) is a relative measure of the resistance of a (stabilized) material to oxidative decomposition. Oxidative-Induction Temperature (dynamic OIT) or Oxidative-Onset Temperature (OOT) is a relative measure of the resistance of a (stabilized) material to oxidative decomposition.OIT, in an oxygen atmosphere
Correction measurementtaking a correction measurement into consideration (e.g. buoyancy for TGA)
Curve evaluationSmoothing of the measurement curvesavoid too high of a smoothing factor
Correction of the baselineBeFlat® for DSC
Correction of the time constant and thermal resistanceTau-R® Mode for DSC
Evaluation standardsISO 11357 for midpoint temperature of the Glass Transition TemperatureThe glass transition is one of the most important properties of amorphous and semi-crystalline materials, e.g., inorganic glasses, amorphous metals, polymers, pharmaceuticals and food ingredients, etc., and describes the temperature region where the mechanical properties of the materials change from hard and brittle to more soft, deformable or transition or linear baseline for enthalpy of melting for DSC
Advanced calculationsdegree of crystallinity, Solid Fat Content (SFC), kinetic analysis