Why Is DMA That Important?

When measuring polymer materials with a DSC (Differential Scanning Calorimeter), it can be difficult to monitor effects such as the Temperatura de Transición VítreaThe 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 rubbery.glass transition. By means of DSC instruments, only the energetic effects of materials (endothermal/ExotérmicoA sample transition or a reaction is exothermic if heat is generated.exothermal) are measured, i.e., the change in specific heat. With a DMA (Dynamic Mechanical Analyzer), however, it is not possible to detect energetic effects since the real mechanical material behavior is determined, and its change in mechanical properties (especially during the glass transition) is much more sensitive compared to energetic effects.

Figure 1 shows a typical DSC measurement on PTFE. Only two small endothermal effects can be seen from the change in crystalline structure. No more information can be gathered, although PTFE provides much more information.

Presented in figure 2 is a direct comparison of the DSC and DMA measurements on PTFE. The red curve shows the DSC results and the black curve the DMA results. The continuous black line represents the storage modulus, E’ (stiffness), and the black dashed curve the loss factor tand (damping). In the DMA measurement, it can clearly be seen that definitely more information is obtained compared to DSC. At the beginning in the low-temperature range a transition represented by the drop in storage modulus, E’, at -124°C (E’ onset) with a corresponding maximum in the loss factor, tand, at -104°C (tand peak) can be observed. This is the β-transition of PTFE. Another transition is found in the storage modulus, E’, at 19°C (E’ onset) which represents the solid/solid transition of PTFE that is also measurable by DSC. This transition is also associated with a peak maximum in the loss factor, tan d, at 29°C (tan d peak).
 

The glass transition of PTFE can be found at higher temperatures by the drop in storage modulus, E’, at 113°C with a corresponding peak maximum in the loss factor, tan d, at 128°C.

It can clearly be seen that DMA is a very sensitive method to detect Phase TransitionsThe term phase transition (or phase change) is most commonly used to describe transitions between the solid, liquid and gaseous states.phase transitions of materials, which are nearly impossible to detect by means of DSC.