Preparation, characterization, and mechanical properties of some microcellular polysulfone foams

Several polymers were evaluated as candidates for the production of high-performance microcellular closed-cell foams. The polymers involved were a polysulfone, a polyethersulfone, a polyphenylsulfone, a polyetherimide, and a poly(ether ketone ketone), and their suitability was gauged by measuring rates at which they could be impregnated with carbon dioxide under pressure at room temperature. This step is essential to the subsequent step of heating the impregnated samples at various temperatures to create foamed structures. The present study focused primarily on the use of the polysulfone in this regard. Microcellular foams of this polymer were found to have average cell sizes in the range 1-10 Am and cell densities on the order of 10(10)-10(14) cells/cm(3). The microstructures of these foamed samples were controlled through careful choices of the foaming temperature and the foaming Speed to produce a wide range of foam densities, Since these materials were prepared for possible use as structural materials, tensile tests were conducted to investigate the dependence of some of their mechanical properties, on the foam densities (relative to those of the unfoamed polymer). The result,, indicated that the tensile moduli of these polysulfone foams increased with the square of their relative densites, and the tensile strengths were proportional to these densities. Both of these experimental findings are in agreement with theory. (C) 2002 Wiley Periodicals, Inc.