DMA Brochure 1 - TA Instruments

APPLICATIONSMEASUREMENT OF Tg OF A PRESSURESENSITIVE ADHESIVE (PSA)A common measurement on polymers is the glasstransition temperature, Tg. It can be measured withvarious techniques, but DMA is by far the mostsensitive. Figure 3 shows a scan of a pressuresensitive adhesive run in the tension clamps at afrequency of 1 Hz. Tg can be measured by theE l onset point, by the E ll peak, or the peak of Tan δ.In addition to the Tg, the absolute value of thevarious viscoelastic parameters is also useful.FREQUENCY EFFECT ON MODULUSAND GLASS TRANSITION OFPOLYETHYLENE TEREPHALATE (PET)Because the Tg has a kinetic component, it isstrongly influenced by the frequency (rate) ofdeformation. As the frequency of the test increases,the molecular relaxations can only occur at highertemperatures and, as a consequence, the Tg willincrease with increasing frequency as illustrated inFigure 4. In addition, the shape and intensity of theTan δ peak as well as the slope of the storage modulusin the transition region will be affected. Basedon end-use conditions, it is important to understandthe temperature and frequency dependence oftransitions.THE MEASUREMENT OF SECONDARYTRANSITIONS IN VINYL ESTERDMA is one of the only techniques that can measureβ and γ secondary transitions. Secondary transitionsarise from side group motion with some cooperativemotion from the main chain as well as internalmotion within a side group. The transitions, asshown in Figure 5, are below the Tg and typicallysubambient. They are very important as they affectimpact resistance and other end-use properties. Thisdata was generated using 3-point bending and alsoillustrates the ability to run stiff composites.