Polymer Plasticization Using Supercritical Carbon Dioxide:  Experiment and Modeling

Abstract

The most important effect of sorption of compressed gases and supercritical fluids into glassy polymers is the reduction of the glass transition temperature (Tg). This plasticization effect causes changes in mechanical and thermophysical properties of the polymers. In this work, a thermodynamic study based on experimental and theoretical results is addressed. New data were carried out for poly(2,6-dimethylphenylene oxide) (PPO), poly(acrylic acid) (PAA), and the copolymer vinylpyrrolidone−vinyl acetate [P(VP−VA)] using an inverse gas chromatographic technique. To model the Tg behavior of diluent−polymer systems, a model that couples the lattice-fluid equation of state and the Gibbs−DiMarzio criterion was used. A parametric study of the influence of the physical properties (lattice coordination number, molecular weight, and binary interaction parameter) on the Tg behavior is presented. The thermodynamic model fairly describes the experimental data measured in this work and gives a phenomenological representation of the retrograde vitrification for the systems PPO−CO2, PVP−CO2, and P(VP−VA)−CO2.