Manufacture and model calculation of porcelain-like microcellular low-density polystyrene foam

It is a well known that nucleation by gases in the supercritical state lead to high-density nanocellular foams, but the aim of this article was to find a route to microcellular low-density closed-cell foam with expected low heat conductivity and high mechanical properties. Polystyrene was impregnated with carbon dioxide or propane at room temperature and 70 bar pressure. Pentane served as a reference substance. The samples were investigated by electron microscopy. The specimens comprising carbon dioxide and propane showed bubbles surrounded by a ring of lamellas. The samples were foamed in hot bathes of silicone, of saturated NaNO₃ water solution, and in water vapor under stretching conditions at 100℃ or 110℃. The foaming was registered continuously on a balance by buoyancy experimentally and calculated in diffusion as well as viscosity-controlled foaming models. A microcellular foam with 35 kg/m³ density, 1.5 µm or 1500 nm cell diameter, 5.5 MPa tear strength, and 0.027 W/m.K heat conductivity was obtained, which looked like porcelain. The continuous manufacture of low-density carbon dioxide or propane foam by extrusion did not lead to microcellular foam, because the necessary high-pressure, low-temperature nucleation conditions could not be performed.