Dynamic Mechanical Analysis
ASTM D4065, D4440, D5279
Dynamic Mechanical Analysis (DMA) is a widely used technique for evaluating the mechanical properties of polymeric materials. The technique measures the elastic modulus (or storage modulus, G'), viscous modulus (or loss modulus, G''), and damping coefficient (Tan D) of materials as a function of temperature, frequency or time. DMA is used for quality control, product development and identifying the transition regions in plastics.
Standards like ASTM D4065, D4440, and D5279 govern the use of DMA. The results of the test are typically provided as a graphical plot of G', G'', and Tan D versus temperature. DMA can identify small transition regions that are beyond the resolution of DSC (Differential Scanning Calorimetry), and as such, DMA is more sensitive.
During the test, the specimen is clamped between movable and stationary fixtures and enclosed in a thermal chamber. The analyzer applies torsional oscillation to the test sample while slowly moving through the specified temperature range. The input parameters include frequency, amplitude, and a temperature range appropriate for the material.
The test specimens are typically 56 x 13 x 3 mm, cut from the center section of an ASTM Type I tensile bar or an ISO multipurpose test specimen.
The key properties that can be determined using DMA are the Tan Delta and complex modulus. The Tan Delta is the ratio of G'' to G', which is the relative degree of damping of the material. This property is an indicator of how efficiently a material loses energy to molecular rearrangements and internal friction. The complex modulus is the vector sum of the storage (Elastic) G' and loss (viscous) G'' components.
Various techniques can be used to determine the glass transition temperature (Tg) by DMA, such as the peak on the Tan Delta curve, peak on the loss modulus curve, half height of storage modulus curve, and onset of storage modulus curve. It is essential to specify the method used to determine Tg because the difference between the techniques can vary by as much as 25°C. DMA Tg is often about 10°C higher than DSC Tg.
In our opinion, DMA is a powerful technique used for the mechanical analysis of polymeric materials. It provides valuable information about the properties of materials, such as the elastic modulus, viscous modulus, and damping coefficient, and can identify small transition regions that are beyond the resolution of other techniques. The technique is used for quality control, product development, and to identify the transition regions in plastics.