Microcellular foams are classified as foams with cell sizes between 0.1 – 10 µm and cell nucleation densities between 10⁹ and 10¹⁵ cells/cm3. In previous studies it has been found that microcellular foams have significantly improved impact toughness relative to the polymer matrix. Microcellular foams are created by saturating a polymer matrix with carbon dioxide or nitrogen at high pressures and rapid release of the gas at temperatures near the glass transition temperature of the polymer. If the gas is a plasticizer for the polymer and reduces its glass transition temperature, then improved control of bubble growth within the polymer is possible. As the foaming proceeds and the gas is rapidly released, vitrification occurs rapidly leading to a small, closed cell structure. In some cases it is possible to obtain high density reductions as well.

In this study, microcellular foams of poly(ether sulfone) (PES), were created with varying density reductions. Density reductions as high as 85% were achieved using a benign process. Nanocomposites of PES and Cloisite Na+ were also foamed. The Cloisite Na+ acts as a nucleating agent leading to a smaller cell size than neat PES. The closed cell structures obtained along with the low density reductions show a promise for use in applications of strong, lightweight materials.