Production of Microcellular Polycarbonate Using Carbon Dioxide for Bubble Nucleation

A process to produce a family of novel materials from polycarbonate, having a microcellular structure, is described. The process utilizes the high solubility of carbon dioxide in polycarbonate to nucleate a very large number of bubbles, on the order of 1 to 10 × 10⁹ bubbles/cm³, at temperatures well below the glass transition temperature of the original, unsaturated polycarbonate. Microcellular polycarbonate foams with homogeneous microstructure and a wide range of densities have been produced. In this paper experimental results on solubility, bubble nucleation, and bubble growth in the polycarbonate-carbon dioxide system are presented, and the critical ranges of the key process parameters are established. It is shown that the bubble nucleation phenomenon in polycarbonate near the glass transition temperature is not described by classical nucleation theory.