Simultaneous measurement of the solubility of gases in polymers and of the associated volume change

Abstract

A new instrument to measure simultaneously the solubility of gases in polymers and the associated volume changes of the polymer is presented. The quantity of penetrating fluid introduced in the system is evaluated by pressure decay measurements in a calibrated volume, while a vibrating-wire force sensor is employed to weigh the polymer sample during sorption inside the high-pressure equilibrium cell. The combined use of the two techniques is required by the nature of the sorption process, since the effects of swelling and solubility processes cannot be isolated by performing one single gravimetric or pressure decay measurement. The knowledge of the equation of state of the gas is required, as well as an estimation of its viscosity. The present instrument accepts polymer samples of about 5 g, and operates at temperatures up to 473 K and pressures up to 100 MPa. The technique was validated by measuring the sorption of nitrogen in polystyrene. The instrument showed a sensitivity of the order of 1 mg of dissolved gas and is capable of detecting a volume change of 0.05% of the initial volume of the polymer. The same principles exposed in the present work can be adapted to other kinds of sorption studies.