DMA Brochure 1 - TA Instruments

CHARACTERIZING PACKAGING FILMSUSING CREEPIn a thermoforming process, a film is pulled downinto a heated mold to form a desired shape. Theability to produce a stable product can be predictedby using a creep-recovery experiment. Figure 9illustrates data on a packaging film using the tensionmode. In the recovery phase, the equilibriumrecoverable compliance, Jer can be calculated. If thesample compliance is too high, as observed by a highJer, then the elasticity may be too low at the formingtemperature to maintain the desired shape.SHEET MOLDING COMPOUND CUREFigure 10 shows the cure profile of a sheet moldingcompound using the shear mode. In thisexperiment, the sample was heated to 150˚C andthen held isothermally. Data was collected vs. time.The sample first softens then begins to cure,reaching a final maximum modulus. This profile willbe influenced greatly by the heating profile. Anassessment can be made on the trade-off in physicalproperties for various cure profiles by conductingthis experiment under various conditions.PREDICTING MATERIAL PERFORMANCEUSING TIME/TEMPERATURESUPERPOSITIONING(TTS)The TTS technique, well grounded in theory, is usedto predict material performance at frequencies or timescales outside the range of the instrument. Data isusually generated by scanning multiple frequenciesduring an isothermal step-hold experiment over atemperature range. A reference temperature is selectedand the data shifted. A shift factor plot is generatedand fit to either a William-Landel-Ferry (WLF) orArrhenius model. Finally, a master curve at a specifictemperature is generated as illustrated in Figure 11for a PET film sample. Using this technique, propertiesat very high frequencies (short time scales) or verylow frequencies (long time scales) can be assessed.E' Master CurveT r =75˚C1.0E-15 1.0E-8 1.0E-1 1.0E6 1.0E13 1.0E20