Batch foaming of SAN/clay nanocomposites with scCO2: A very tunable way of controlling the cellular morphology

This paper aims at elucidating some important parameters affecting the cellular morphology of poly (styrene-co-acrylonitrile) (SAN)/clay nanocomposite foams prepared with the supercritical CO2 technology. Prior to foaming experiments, the SAN/CO2 system has first been studied. The effect of nanoclay on CO2 sorption/desorption rate into/from SAN is assessed with a gravimetric method. Ideal saturation conditions are then deduced in view of the foaming process. Nanocomposites foaming has first been performed with the one-step foaming process, also called depressurization foaming. Foams with different cellular morphology have been obtained depending on nanoclay dispersion level and foaming conditions. While foaming at low temperature (40 degrees C) leads to foams with the highest cell density ((similar to 10(12)-10(14) cells/cm(3)), the foam expansion is restricted (d similar to 0.7-0.8 g/cm(3)). This drawback has been overcome with the use of the two-step foaming process, also called solid-state foaming, where foam expansion occurs during sample dipping in a hot oil bath (d similar to 0.1-0.5 g/cm(3)). Different foaming parameters have been varied, and some schemes have been drawn to summarize the characteristics of the foams prepared - cell size, cell density, foam density - depending on both the foaming conditions and nanoclay addition. This result thus illustrates the huge flexibility of the supercritical CO2 batch foaming process for tuning the foam cellular morphology. (C) 2010 Elsevier Ltd. All rights reserved.