Fabrication of microporous PMMA using ionic liquids: An improved route to classical ScCO2 foaming process

The use of supercritical CO2 (ScCO2) has been established as a standard technique to produce micro- and nanocellular polymers with controlled morphologies and cell sizes between 500 nm and several microns. However, overcoming the gap between micro and nanocellular polymers implies the use of long saturation times (up to several days) and low temperatures (below 0 degrees C) combined with high saturation pressures (above 30 MPa). This work presents a different approach to obtain microporous poly (methyl methacrylate) (PMMA) structures with controlled morphologies using a physical procedure employing ionic liquids that are mixed in solution with PMMA. The ionic liquid can produce interesting fine microporous materials simply by being removed with distilled water. The work compares the two fabrication methods previously mentioned to critically analyze the benefits and drawbacks of each preparation route. The method in this paper opens the possibility to obtain microporous polymers by employing ionic liquids, thus reducing the time of processing, avoiding specific foaming equipment and broadening the applicability of crosslinked and semi crystalline polymers. Low velocity tensile test results are also presented to point out the improvement in the mechanical parameters of microporous films obtained from ionic liquids compared to those of films foamed using ScCO2.