Plasticization of [C12MIM][PF6] Ionic Liquid on Foaming Performance of Poly(methyl methacrylate) in Supercritical CO2

A series of poly(methyl methacrylate) (PMMA)/1-dodecyl-3-methylimidazolium hexafluorophosphate ionic liquid a [C12MIM][PF6] blends were prepared by melt blending. The compatibility of blends was verified by scanning electron microscopy and differential scanning calorimetry. The introduction of [C12MIM][PF6] decreased the glass transition temperature of the blends due to its plasticization effect and increased the diffusivity of CO2 without significantly affecting the CO2 solubility. These blends were foamed with supercritical CO2 as the blowing agent via a pressure-quenching process. The foaming conditions are divided into three regions according to the main morphological difference of foams. At relatively low temperatures and pressures, neat PMMA could not be foamed, while the addition of [C12MIM][PF6] facilitated the formation of cells. By increasing temperature or pressure, neat PMMA foams were obtained with wide cell size distribution, while the blend foams were formed with narrowed cell size distribution and increased cell size. At high temperatures and pressures, neat PMMA was foamed with narrow cell size distribution and high cell density, while the major effect of [C12MIM][PF6] was to increase the cell size. These results indicated that the plasticization effect and the low surface energy of [C12MIM][PF6] accounted for the differences on the cell morphology between neat PMMA and the blend foams.