The specific volume of poly(tetrafluoroethylene) as a function of temperature (30°–372°C) and pressure (0–2000 kg/cm2)

Abstract

SynopsisExperimental data on the specific volume of a 50% crystalline sample of poly(tetrafluorethy1ene) are presented and discussed. Data points were taken along 22 isotherms spaced 5 to 3OoC apart (up to 372OC) in pressure increments of 100 kghm2 up to ZOO0 kg/cm2. In addition to the melting transition and the first-order solid-solid transition near room temperature, a previously reported second-order transition near 14OOC at P = 0 is observed. This transition shifts to higher temperatures with increasing pressure by about 0.015OC per kg/cm2. The melt data are discussed in detail. They can be fitted to both the empirical Tait equation, with the usual exponential temperature dependence of the Tait parameter, and to the Simha-Somcynsky hole theory (with the reducing parameters V* = 0.424 cm3/g, T* = 7906OK, and P* = 7100 kg/cm2 = 6960 bars), thus providing a test for this theory at high reduced temperatures near = 0.08.

Phase Behavior of Polymers in Supercritical Fluid Solvents

“…One is hydrostatic pressure that increases the melting temperature at a rate of ∼1.0 °C/10 bar, which is the rate observed for PTFE. 128,129 The other effect is the melting point depression of FEP 19 that results from the solubility of CF 4 in the FEP 19 -rich liquid phase. Thus, while 2000 bar of hydrostatic pressure raises the melting point of pure FEP 19 from 147 °C to ∼347 °C, the presence of CF 4 in the FEP 19 -rich liquid-phase reduces the temperature of crystallization to ∼189 °C at the same pressure.…”

Modeling of the Sorption and Swelling Behavior of Semicrystalline Polymers in Supercritical CO2

“…The resulting values of m/M W and u 0 /k are reported in Table 3. Then, the Kouskoumvekaki method was applied and V 00 was fitted to PTFE density data at different temperatures and pressures 71 to obtain a set of pure component parameters for PTFE. However, subsequently using these values to describe the sorption and swelling PTFE-CO 2 results did not lead to a reasonable description of the data for any value of the interaction ψ.…”

The heat of fusion of polytetrafluoroethylene

“…The equilibrium PVT properties of PTFE melt were reported in an earlier paper. 8 In the range 330 < T < 370°C the zero-pressure specific volume was given by VO (cm3/g) = 0.3200 + 9.586 X 10-4T ("C) In ref. 8 the pressure dependence of the specific volume was also fitted to the Tait equation.…”

“…8 In the range 330 < T < 370°C the zero-pressure specific volume was given by VO (cm3/g) = 0.3200 + 9.586 X 10-4T ("C) In ref. 8 the pressure dependence of the specific volume was also fitted to the Tait equation. From the coefficients of the Tait equation, the zero-pressure compressibility of the melt can be expressed as KO (cm2/kg) = -(w) = 2.06 X lod5 exp[9.38 X 10-3T ("C)] bP TIP=O In order to measure the pressure dependence of the melting point we performed a series of isobaric heating experiments at a heating rate of 1.4"C/min at selected pressures between 50 and 700 kg/cm2.…”

“…This was the same material that we had used in our previous PVT work. 8 It had a density of 2.151 g/cm3, giving a crystallinity of 53%, again assuming no voids. Compared to the virgin polymer, T, is lower, AVm is smaller, and the melting range is broadened.…”