Foaming of PCL/clay nanocomposites with supercritical CO₂ mixtures: The effect of nanocomposite fabrication route on the clay dispersion and the final porous structure

Supercritical fluids have been established as alternative foaming agents in various polymers as well as nanocomposite systems. Most recently, supercritical carbon dioxide (scCO₂) has also been used in some studies as a medium of clay dispersion in the polymer matrix providing a solvent-free fabrication route for nanocomposites. In this work, this latter route was followed for the development of porous poly(ε-caprolactone) (PCL)/clay nanocomposites after pressure quench. Similarly, PCL/clay nanocomposites were also prepared using the solvent casting and melt blending methods and were then processed with scCO₂ with the batch foaming technique (isothermal pressure quench) to produce their porous counterparts. Poor clay dispersion and non-uniform porous structures were observed when pure CO₂ was used as a dispersion medium for nanocomposite preparation and as a blowing agent, respectively. On the contrary, polymer intercalation and more uniform cell structures were produced when CO₂-ethanol mixtures were used as blowing agents.