Ultrasonic investigation of semicrystalline polymers: study of poly(ethylene terephthalate)

Abstract Ultrasonic velocity and attenuation were measured as functions of temperature (20 to 320°C) and hydrostatic pressure up to 900 bar at acoustic frequencies varying from 1 to 6.33 MHz on semicrystalline poly(ethylene terephthalate). Melting, α-relaxation and glass transition temperatures and their dependence on pressure were determined from the variations of ultrasonic characteristics. Comparison with very low-frequency (1–10 −1 Hz) dynamic mechanical spectroscopy is done in the case of α-relaxation, which can be described in terms of a Vogel-Fulcher-Tammann relation. With simultaneous specific volume measurements, glass transition temperature is determined by different methods to validate ultrasonic results. In particular, data analysis through a physical model is described to improve the method in the case of semicrystalline polymers.