Morphological changes of the polylactic acid microstructure under the action of supercritical carbon dioxide

The microstructure and properties of amorphous D,L-polylactide subjected to different treatments in supercritical carbon dioxide (SC-CO2) were investigated. Atomic force microscopy analysis demonstrated that plasticization and subsequent foaming of the polymer in SC-CO2 leads to significant changes in its internal structure, which are caused by the rearrangement of the supramolecular structure of polylactic acid. The formation of micro and meso pores and an accompanying increase of polylactide void volume are directly related to the destruction of polymer initial intermolecular bonds during the release of SC-CO2. These changes facilitate the formation of thermodynamically more stable conformations, which is manifested in a significant (1.7–5.0-fold) increase of the values of exothermic effects registered by differential scanning calorimetry in the temperature range from −30 to −10°C and near 30–40°C.