The modern DMA is a high sensitivity device that measures Storage Modulus (stiffness) and the Loss Modulus (energy dissipation) of viscoelastic materials as they are subjected to oscillatory stresses (or forces) and resultant strains (displacements). The new instruments operate in precise temperature control from the cryogenic region to over 600°C, and can evaluate materials ranging from rigid composites to weak gels. As such, the DMA can accurately determine the glass transition region and factors that affect these processes.

Examples:

Stress Induced Crystallization in PET

In a biomedical application it was important to compare the performance of an existing product with a newly synthesized and fabricated material. Careful annealing with the existing product had shown a consistent T_g at 91°C. In addition, the existing product was oriented and had a crystalline component that melted above 200°C. DMA experiments on the new PET polymer showed an unexpected increase in the Storage Modulus just above 30°C. The Loss Modulus peak (and Tan d) also moved up over five degrees. These results were the basis for an early warning that the new material needed more annealing cycles before being submitted for final fabrication.

Detection of Polymer Blends

DMA of Polymer Blend

Two polymers were mixed in a melt at various compositions and formed into small test bars. The samples were analyzed via DMA using the dual cantilever apparatus over the range –100 to 140°C. The results showed two peaks in the Loss Modulus (E´´), which merged into one at a critical composition. Further tests on the product indicated unique strength properties associated with the blend.

The DMA method has been found to be the most direct and cost-effective technique to screen new polymers for potential blend-formers.