Simultaneous measurement of the concentration of a supercritical gas absorbed in a polymer and of the concomitant change in volume of the polymer. The coupled VW-pVT technique revisited

Abstract

The purpose of this article is to re-examine the simultaneous measurements of the concentration of a supercritical gas in a polymer and of the concomitant change in volume of the polymer with the coupled VW-pVT technique [Hilic S, Pádua AAH, Grolier J-PE. Rev Sci Instrum 71 (11) (2000) 4236–41; Hilic S, Boyer SAE, Pádua AAH, Grolier J-PE. J Polym Sci B: Polym Phys 39 (2001) 2063–2070]. The experimental set-up consists of an original coupling of two techniques, a vibrating-wire sensor VW to weigh the polymer sample during the sorption and a pressure decay pVT-method to measure the quantity of gas, transferred from a high-pressure calibrated volume, which is absorbed by the polymer sample. The present study is related to the sorption and desorption of light gases (like CH4, CO2, H2S, N2) usually found in petroleum products circulating in pipelines made of semicrystalline polymers (like polyolefins and fluorinated polymers).Results for CO2 in medium-density polyethylene, MDPE, and in poly(vinylidene fluoride), PVDF (or PVF2), in the range of temperatures up to 391K and pressures up to 43MPa, are reported and discussed. Experiments allow the apparent concentration of gas dissolved in the polymer to be established; the associated swelling of the polymer is estimated using the Sanchez–Lacombe equation of state. Then, the data of the corrected concentration of the gas in the polymer are correlated with the semi-empirical ‘dual-mode’ model. Whenever possible to compare our results are in good agreement with existing literature data.