CO₂-Induced PMMA Swelling and Multiple Thermodynamic Property Analysis Using Sanchez−Lacombe EOS

Abstract

The Sanchez−Lacombe equation of state (SL EOS) is often used to describe polymer−gas systems because of its inherent ability to hand compressible fluids, but it has rarely been tested for correlating multiple thermodynamic properties of these systems. The real value of an EOS as a process design tool is the ability to describe all thermodynamic properties, not just those it has been fit to. Because of the relatively small amount of data for polymer−gas systems, there is no heuristic to determine which property should be used to fit the EOS to give the best representation of other properties. We test this idea by looking at dilation, solubility and T g in the CO 2 −PMMA system. Although CO 2 sorption phenomena in polymers have been extensively investigated, the study of CO 2 -induced polymer dilation is rather limited in comparison. A new experimental technique based on ADSA (axisymmetric drop shape analysis) was developed in this work to measure volumetric properties. The dilation isotherm was measured over temperatures of 40−200 °C and pressures up to 100 bar. The experimental swelling data are then modeled using the SLEOS and the correlated interaction parameter between gas and polymer decreases linearly with temperature within the range 40−160 °C. The applicability of SLEOS to describing thermodynamic behavior of gas−polymer mixture is demonstrated by successfully predicting the CO 2 sorption at 30−60 °C and T g depression.