Production of controlled polymeric foams by supercritical CO2

The foaming of polystyrene and cellulose acetate has been studied using a technique based on the saturation of the polymer by supercritical CO2 and the rapid decompression of samples. The diameter of resulting microcellular structures has been controlled manipulating the process conditions. The experiments performed at various foaming temperatures (from 55 to 125 °C for polystyrene and from 215 to 245 °C for cellulose acetate) and at 230 bar for polystyrene and at 250 bar for cellulose acetate, showed that higher temperatures produce larger cells (with mean diameters from 5 to 65 μm for polystyrene and from 7 to 70 μm for cellulose acetate). The effect of foaming pressure has been also tested, at T = 75 °C for polystyrene and at T = 230 °C for cellulose acetate, from 80 to 230 bar for polystyrene and from 100 to 250 bar for cellulose acetate. Larger pressures generate smaller cells with mean diameters from 60 to 15 μm for polystyrene and from 80 to 20 μm for cellulose acetate. The influence of the contact time has also been studied: from 60 to 240 min for polystyrene and from 180 to 480 min for cellulose acetate; larger contact times assure homogeneous CO2 diffusion inside the sample and, consequently, a symmetric microcellular structure.