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

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 391 K and pressures up to 43 MPa, 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.