Determination of Pressure Dependence of Polymer Phase Transitions by pVT Analysis.

Jürgen Pionteck

doi:10.3390/polym10060578

Abstract

Glass transitions, melting, crystallization, and the isotropization of polymers are connected with changes in the density, respectively the specific volume (Vsp), which can be analyzed by dilatometric methods. Here, the pressure dependence of such transitions is determined by pressure volume temperature (pVT) analysis for different thermoplastic polymers in the pressure range of 10 to 200 MPa, and the temperature range from room temperature to 350 °C. The values for ambient pressure are extrapolated. It is shown that polymer transitions always increase with pressure, and that the melting temperature and glass transition temperature are nearly linearly dependent on pressure. This information, as well as the observed density changes with pressure and temperature, is very important for the processing of thermoplastics, including their simulation, as well as for the thermodynamic interpretations of the transition’s nature.

Highlights

Phase transitions of polymers are typically determined at environmental pressure, which is sufficient for many purposes
It is shown that pressure volume temperature (pVT) analysis is a suitable tool for determination of the pressure dependence of the phase transitions of polymers
To obtain accurate data and data interpretation, the thermal and pressure history must be known, since the semi‐crystalline and the glassy state are always in non‐. Equilibrium, and these states depend on the conditions in which they were reached

Summary

Introduction

Phase transitions of polymers are typically determined at environmental pressure, which is sufficient for many purposes. The crystallinity and the crystal morphology depend on the thermal history, so that changed crystallization conditions result in different density changes, e.g., slow cooling commonly generates a higher degree of crystallization than fast cooling, and increasing pressure shifts the glass transition and crystallization temperature to higher values, and may even cause different crystallite morphologies. Tg , in contact with the stiff crystals, the mobility of amorphous polymer chains may be hampered due to interaction with the crystals This part is called the “rigid amorphous phase”, which is in a non-equilibrium state, while the “mobile amorphous phase” can more or less follow changes in the outer conditions by changing its specific volume.

Materials and Methods

Pressure Dependence

Discussion