ASTM E1640-23 Standard Test Method for Determining Glass Transition Temperature by Dynamic Mechanical Analysis

The standard "ASTM E1640-23 Standard test method for determining glass transition temperature by dynamic mechanical analysis" developed by the American Society for Testing and Materials (ASTM) describes a test method that involves determining the glass transition temperature (Tg) of materials using dynamic mechanical analyzers. This test method is applicable to thermoplastic polymers, thermoset polymers, and partially crystalline materials that are thermally stable in the glass transition region.

The temperature range for this test method depends on the instrumentation used, but the minimum temperature should be approximately minus 150 degrees to cover all materials.

This test method is designed for materials with elastic modulus in the range of 0,5 MPa to 100 GPa.

Specific technical terms used in this standard are included in “ASTM D4092-21 Standard terminology for plastics: dynamic mechanical properties” and “ASTM E1142-15 Standard terminology related to thermophysical properties”, including Celsius, dynamic mechanical analyzer, glass transition, glass transition temperature, loss modulus, storage modulus, tangent delta, and viscoelasticity.

In conducting tests, a sample of known geometry is placed in mechanical oscillation at a constant or resonant frequency and changes in the viscoelastic response of the material are monitored as a function of temperature. Under ideal conditions, during heating, the glass transition region is marked by a rapid decrease in the storage modulus and a rapid increase in the loss modulus and tangent delta.

The glass transition of the test sample is indicated by the extrapolated onset of decrease in storage modulus, which marks the transition from a glassy solid to a rubbery solid.

This test method can be used to find the glass transition region of amorphous and semicrystalline materials and assign the glass transition temperature. Dynamic mechanical analyzers provide a way to measure these changes by monitoring changes in the viscoelastic properties of a material as a function of temperature and frequency. In ideal cases, the onset temperature of the decrease in storage modulus marks the glass transition.

The glass transition occurs over a temperature range. This method assigns a single temperature (Tg) to represent the temperature range measured by dynamic mechanical analysis. Tg can be determined by a variety of techniques and can vary with that technique.

A glass transition temperature (Tg) is useful in characterizing many important physical properties of thermoplastic, thermoset, and semicrystalline materials, including their thermal history, processing conditions, physical stability, progression of chemical reactions, degree of cure, and both mechanical and electrical behavior.

This test method is found useful for quality control, specification acceptance and research.

Since sample size will usually be small, it is essential that each sample be homogeneous or representative of the material as a whole, or both. An increase or decrease in heating rates from those specified may alter the results.

A transition temperature is a function of the experimental frequency, so the test frequency should always be specified. (Transition temperature increases with increasing frequency). Extrapolation to a common frequency can be accomplished by using a predetermined frequency shift factor or by assuming a frequency shift factor of approximately 8 degrees for each decade of frequency. Such extrapolations should be reported.

The function of the apparatus used in these tests is to hold a sample of uniform size in such a way that the sample acts as an elastic and dispersive element in a mechanically oscillating system. Dynamic mechanical analyzers generally operate in one of several modes.

This device includes:

• Clamps are a clamping arrangement that allows the specimen to be gripped. Specimens can be mounted by clamping at both ends (in most systems), one end (e.g. torsion pendulum), or neither end (free bending between the blade edges).
• Oscillatory stress is the process of applying an oscillatory deformation (stress) or oscillatory stress to a sample. The deformation can be applied and then released, as in freely vibrating devices, or it can be applied continuously, as in forced vibration devices.
• Detector for determining dependent and independent experimental parameters such as force (or stress), displacement, frequency and temperature. Temperatures should be readable to plus/minus 0,1 degrees, force to plus/minus 1 percent and frequency to plus/minus 0,1 Hz. The temperature sensor should be placed as close as possible to the test sample but without contact.
• The temperature controller and oven are for controlling the temperature of the sample by heating, cooling or providing a constant experimental environment. The temperature programmer must be stable enough to allow the temperature of the sample to be measured to plus/minus 0,5 degrees. The required temperature measurement accuracy is plus/minus 1,0 degrees.
• A data acquisition device is intended to provide a means of acquiring, storing, and displaying measured or calculated signals, or both. The minimum output signals required for dynamic mechanical analysis are the storage modulus, loss modulus, tangent delta, temperature, and time. Some devices suitable for this test may display only linear or logarithmic storage modulus, while others may display linear or logarithmic storage modulus, or both. Care should be taken to use the same modulus scale when comparing unknown samples and when comparing results from one device to another.
• Nitrogen, helium or other gases are supplied for purging purposes. The same purging gas is used for calibration and measurement of the test sample.
• Calipers or other length measuring devices are for measuring dimensions (or lengths) to plus/minus 0,01 mm.

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