Preparation and morphology characterization of microcellular styrene‐co‐acrylonitrile (SAN) foam processed in supercritical CO2

Abstract

Microcellular polymeric foam structures have been generated using a pressure-induced phase separation in concentrated mixtures of supercritical CO2 and styrene-co-acrylonitrile (SAN). The process typically generates a microcellular core structure encased by a non-porous skin. Pore growth occurs through two mechanisms: diffusion of CO2 from polymer-rich regions into the pores and also through CO2 gas expansion. The effects of saturation pressure, temperature and swelling time on the cell size, cell density and bulk density of the porous materials have been studied. Higher CO2 pressures (hence, higher fluid density) provided more CO2 molecules for foaming, generated lower interfacial tension and viscosity in the polymer matrix, and thus produced lower cell size but higher cell densities. This trend was similar to what was observed in swelling time series. While the average cell size increased with increasing temperature, the cell density decreased. The trend of bulk density was similar to that of cell size. © 2000 Society of Chemical Industry