Quasi-Adiabatic Expansion of the Polylactide Foam: Features of the Porous Matrices Formation in the Region of Transition between Sub- and Supercritical States of Plasticizing Carbon Dioxide

—Experimental data are presented on the dynamics of quasi-adiabatic expansion of the foam formed from carbon-dioxide-plasticized polylactide in the course of fast depressurization. It is shown that, in the range of initial pressure, which corresponds to the region of transition between the subcritical and supercritical states of plasticizing agent, a substantial increase takes place in the resulting volume of the formed porous matrices. Study of the structure of synthesized matrices at the mesoscopic level provided using low-coherence reflectometry showed a dramatic difference from synthesis conditions far from the transition region. The observed features are interpreted in the framework of a qualitative model using an equation proposed by Ross to represent the foam state. The considered model takes into account the sign of increment of the internal energy of a plasticizing and foaming agent in the course of transition between the initial and final thermodynamics states of the foamed polymer.