Predicting Solubility and Diffusivity of Gases in Polymers under High Pressure: N₂ in Polycarbonate and Poly(ether-ether-ketone)

Abstract

The aim of this study was to develop a model that predicts the gas solubility and the sorption and desorption kinetics in polymer granulates over large temperature and pressure intervals. Besides the part predicting the solubility and diffusivity, the model involves the simultaneous solution of the diffusion equation and the heat equation in three dimensions using a finite element method (FEM). When the temperature-and pressure-dependent solubility of a specific polymer/gas combination is not known, an improved version of the non-equilibrium lattice fluid model (NELF) is used to predict the solubility. The improvement of the NELF model includes the use of Hansen's solubility parameters, and it uses pressure− volume−temperature (PVT) data from two new empirical models, which accurately estimate polymer densities over a wide range of temperatures and pressures. The new solubility model predicted the solubility−pressure data of N 2 in poly(ethyl methacrylate) and N 2 and CH 4 in polycarbonate (PC) at pressures below 4.5 MPa, without using any adjustable interaction parameters. The model was used to predict the solubility of N 2 in poly(ether-ether-ketone) (PEEK) and PC at a very high pressure (67 MPa). Experimental N 2 solubility data were obtained with a specially built reactor yielding high pressure and temperature. For PEEK, it was possible to predict the very high pressure solubility using a gas−polymer interaction parameter obtained from data taken at low pressures. In addition, a new free-volume-based diffusivity model requiring no adjustable interaction parameters was developed, and it successfully predicted the desorption kinetics of N 2 from PEEK and PC.

Influence of high pressures on CH4, CO2 and H2S solubility in polyethylene: Experimental and molecular simulation approaches for pure gas and gas mixtures. Modelling of the sorption isotherms

“…They are of the same order, showing that chain motions are still possible during the sorption process, even at high pressure. In the literature, some authors reported also a decrease of gas sorption at high pressure, assigning this behaviour to a decrease of the material free volume under these conditions [20,[48][49][50]. The swelling of the polymer amorphous phase consecutively to the sorption phenomenon was then determined as a function of the gas nature and sorption conditions.…”

A model to predict the cell density and cell size distribution in nano-cellular foams

“…T g data was obtained from Condo and Johnston (1994). Diffusivity of CO 2 is the polymer was obtained from Nilsson et al (2013). Viscosity as a function of shear rate was obtained using a sliding plate rheometer and fit to a Cross model given in Equation 6.…”

Permeation of a Range of Species through Polymer Layers under Varying Conditions of Temperature and Pressure: In Situ Measurement Methods

“…Nilsson et al [18] measured the permeability, solubility and diffusion coefficients of nitrogen gas in polycarbonate and polyether ether ketone polymers at a pressure of 670 bar and at temperatures in the range of 100 to 250 °C. In contrast, Celina and Gillen [19] used a continuous flow method for measuring the permeability of oxygen through elastomers at pressures of approximately 315 mm Hg and temperatures of 225 °C.…”