Simultaneous determination of sorption, heat of sorption, diffusion coefficient and glass transition depression in polymer-CO2 systems

Polymer-CO2 interactions dictate the evolution of various phenomena such as sorption of CO2, polymer swelling, and polymer plasticization. The knowledge of key quantities and parameters such as the amount of absorbed gas, the heat of sorption, or the diffusion coefficient is of great importance for a rational design of related processes. We have designed and constructed an apparatus based on the combination of Calvet calorimetry and pressure drop method. This combination allows for the determination of the amount of absorbed CO2, the heat of sorption, the diffusion coefficient of CO2 in the polymer and, finally, the concentration of CO2 that causes plasticization of the polymer at a specific temperature (below the atmospheric glass transition temperature). We describe and propose a methodology for the simultaneous measurement of the four, above mentioned, parameters. The glass transition depression is determined by a novel approach which, in addition, allows for information about the kinetics of plasticization to be derived. New results at 54.3 degrees C and at various pressures are presented for the PMMA-CO2 system, and wherever possible, compared with literature data and modeled with the NRHB (Non Random Hydrogen Bonding) model and the dual sorption model. (C) 2011 Elsevier B.V. All rights reserved.