Modeling of pressure-specific volume-temperature behavior of polymers considering the dependence of cooling and heating processes

Few studies have examined the process dependence of the pressure-specific volume-temperature (pvT) behavior of polymers. Especially, the specific volume variation during heating is often ignored, but for certain processing techniques such as plastic welding and additive manufacturing, special consideration should be given. In this study, a new pvT model was proposed to determine the specific volume evolution of polymers during cooling and heating processes. The process dependence of pvT behavior of polymers was discussed in theory, and the influences of starting temperature and cooling/heating rates were considered in the modeling. The pvT behavior of a semi-crystalline polymer, polypropylene (PP), was measured. Mathematical model parameters were determined through the fitting of the experimental pvT data. The fitted results were in good agreement with the experimental data, which showed that the proposed model is accurate and effective. The R2 value of 99.82% and the average absolute percent deviation of 0.21% were obtained. The process dependent pvT model is simple and has broad application prospects in polymer physics and polymer processing. (c) 2020 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).