Ultrasonic characterization of polymer viscoelasticity. Application to polystyrene

Ultrasonics is presented as a powerful method for the thermomechanical analysis of polymers. An experiment is described where the specific volume of a polymer is measured in simultaneity with the acoustic parameters. The technique allows full control of the thermal history in the temperature range from — 150°C to 300°C, where the material goes from a glasslike to a liquidlike state. Moreover the technique allows measurements to be performed at different pressures, up to 2 kbar. Results obtained on a typical amorphous polymer (polystyrene) are reported and the propagation of sound is discussed in regards to the well defined thermodynamic state for the material. Also, the results discriminate between the thermodynamic and the relaxational aspects of the glass transition.