Preparation and characterization of PMMA graded microporous foams via one-step supercritical carbon dioxide foaming

Supercritical carbon dioxide (ScCO2) foaming which is inexpensive and environmental friendly has been widely used to prepare polymer-based microporous materials. In this paper, PMMA graded microporous materials were foamed by PMMA matrix after an unstable saturation process which was done under supercritical condition of 28MPa and 50 °C. The scanning electron microscopy (SEM) was utilized to observe the morphology of the graded foam. A gas adsorption model was proposed to predict the graded gas concentration in the different region of the polymer matrix. The SEM results showed that the solid and foam region of the graded foam can be connected without laminated layers. With the increasing thickness position of the graded microporous foam, the cell size increased from 3.4 to 27.5 μm, while the cell density decreased from 1.04 × 109 to 1.96 × 107 cells/cm3. It also found that the gradient microporous structure of the foam came from graded gas concentration which was obtained in the initial saturation process.