Influence of rheological characterization on modeling of volume retardation processes.

When considering material models describing pressure, specific volume and temperature (pvT) behavior, that are used in engineering practice, one can still find that the used methods comprise sufficient potentials for improvement. In scientific literature the KAHR model is a well-established approach, in order to model time dependent specific volume of amorphous thermoplastics. The KAHR model uses a generalized Kelvin-Voigt retardation time spectrum, along with empirically fitted shift factors for temperature and free volume. The determination of material-specific model parameters is costly, since time consuming temperature-jump experiments, that allow volume retardation at temperatures below glass transition at different pressures, would have to be performed. In previous work, it could be shown, that the underlying rheological information could also be gained using a combination of dynamic mechanical analysis, temperature and pressure dependent viscosity measurements as well as pvt measurements. This work discusses how the sample preparation influences the determination of material parameters using dynamic mechanical analysis. It was shown that the conformation of the polymer molecules frozen during sample preparation has a significant influence on the parameter determination. As expected, the best results can be obtained with samples whose conformation corresponds most closely to the theoretical equilibrium state. [ABSTRACT FROM AUTHOR]