Pressure-Volume-Temperature Melts

An increase in the melting point with increasing pressure (0.154 deg per atmosphere) was reported by McGeer and Duus, and the pressure-volume-temperature relationship of polytetrafiuoroethylene above its melting point was studied in more detail by Lupton who found the following equation of state ... 

The thermophysical properties, such as glass transition, specific heat, melting point, and the crystallization temperature of virgin polymers are by-and-large available in the literature. However, the thermal conductivity or diffusivity, especially in the molten state, is not readily available, and values reported may differ due to experimental difficulties. The density of the polymer, or more generally, the pressure-volume-temperature (PVT) diagram, is also not readily available and the data are not easily convertible to simple analytical form. Thus, simplification or approximations have to be made to obtain a solution to the problem at hand. 

Lucchelli, E. Tomka, I. Vancso, G. Yeh, P. L., "Numerical Evaluation of the Thermodynamic Equation for the State of Polymer Melts from Pressure-Volume-Temperature (PVT) Data," Polym. Bull., 20, 569 (1988). 

The volume of a material is a function of both the temperature T and the pressure p, as described by its pressure-volume-temperature (PVT) relationships. These relationships incorporate a description of the complete phase behavior of a material, such as the significant changes which take place when the material undergoes a phase transition (for example when a solid melts or sublimes, or when a liquid boils). The preceding discussion focused on the dependence of the volumetric properties on the temperature only, at atmospheric pressure, since there are no simple and general quantitative stmcture-property relationships to describe the full PVT behavior. This topic is of great importance, however, and will now be reviewed. 

PRESSURE VOLUME TEMPERATURE RELATIONSHIP FOR POLYMER MELTS... 

Pressure-Volume-Temperature Relationship for Polymer Melts... 

CAP Capt, L. and Kamal, M.R., The pressure-volume-temperature behavior of polyethylene melts, Intern. Polym. Process., 15, 83, 2000. 

There is a near-step increase in specific volume when the crystals in a semicrystalline polymer melt. In the pressure-volume-temperature (p-V-T) data for polyethylene (Fig. 6.10a), the crystalline phase finishes melting at 130 °C... 

Prigogine, Trappeniers, and Mathot pressure-volume-temperature measurements lead zirconate titanate quaternary ammonium salts quasi-two-parameter theory rigid amorphous fraction Rheometrics extensional rheometer Rheometrics elongational rheometer for melts room temperature small-angle neutron scattering small-amplitude oscillatory shear flow small-angle x-ray scattering side-chain LCP... 

Tables in this chapter contain published pressure-volume-temperature data for amorphous homopolymers. Measurements below the melting temperatures for semi-crystalline materials are not included because of the potentially large variance among samples with differing degrees of crystallinity. Rogers [1] and Zoller [2] have also compiled equation-of-state data for amorphous polymers.

Plastic melts are also compressible. Thus, a temperature and pressure change of200°C and 50 MPa, respectively, causes a 10 to 20 percent difference in density, depending on whether the polymer is amorphous or semicrystalline. Specific volume (v), the inverse of density, is often used to relate density to temperature and pressure. As shown in the typical pressure-volume-temperature (pvT) curves presented in Fig. 5.6, specific volume increases with temperature but decreases with increasing pressure. The isobars exhibit significant changes as the polymer passes through its transition temperature this is Tg for amorphous... 

Pressure-volume-temperature (P-V-T) investigations represent an underappreciated area of polymer science and engineering. Such data can be obtained for both polymer solids and melts, sometimes in a single experiment (see the next section). Needless to say, such experiments can be conducted also for materials other than polymeric. The main applications of P-V-T results in the field of polymers are ... 

Estimates of equilibrium melting temperatures of PCL crystallites were made, for various binary and ternary systems, with the aid of Hoffman-Weeks plots. The observed melting points of PCL were between 55 ° C and 65 ° C and varied by about 3 °C with changes in from 38 °C to 48 °C. From the melting-point depressions, as a function of composition and pressure-volume temperature data, Kim and Paul estimated equation-of-state parameters. During the course of this study Kim and Paul determined specific volume data for PCL at a series of hydrostatic pressures (Fig.51) [87]. 

The rheological properties and associated melt-processing characteristics of ethylene-co-styrene polymers, including solid-state DMS, melt strength, and pressure-volume-temperature (PVT) data, have been reported by Kaijala and coworkers (59,60). Rheological master curves were generated via time-temperature... 

Pressure-Volume-Temperature Relationships for Polymer Melts.13-21... 

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