Experimental measurement of CO2 diffusion in PMMA and its effect on microcellular foaming

Abstract The CO 2 diffusion coefficient in polymethyl methacrylate (PMMA) was measured to investigate the relationship between the saturation time and cell nucleation in batch foaming. Measurements were conducted using a visualized high-pressure cell at various temperatures from 303 to 343 K and CO 2 pressures of 6, 12, and 18 MPa. The CO 2 diffusion coefficient depended strongly on the temperature but weakly on the pressure. Additionally, the CO 2 diffusion was promoted by the glass transition behavior of PMMA but was suppressed by the hydrostatic pressure at high pressures. Based on the sorption isotherms of CO 2 in PMMA, microcellular PMMA foams were prepared with saturation times from 1800 to 12600 s. Cell nucleation was initiated when the CO 2 concentration, which depended upon the CO 2 diffusion and saturation time, was sufficient to minimize the energy barrier. Furthermore, the critical CO 2 concentration to initiate cell nucleation decreased with an increase in temperature.