A continuous extrusion process for the manufacture of low-density microcellular polycarbonate (PC) foams using CO₂ is presented. Due to its outstanding mechanical properties and high thermal resistance, polycarbonate foams have been considered as a candidate that will broaden the applications of foams in new industrial areas with high temperature environments.

This thesis presents the effective strategies for increasing the volume expansion ratio and the cell density of polycarbonate foams. The basic strategies are:​ (a) to use sufficiently high pressure all through the extrusion system;​ (b) to use branched material;​ (c) to use high pressure drop rate at the die exit;​ (d) to use sufficiently high contents of CO₂;​ (e) to optimize the processing temperature. The effects of processing and material parameters on foam morphologies were thoroughly studied using a single-screw tandem foam extrusion system. By tailoring the processing and material parameters, polycarbonate foams with an expansion ratio of up to 19 times with a cell density over 10¹⁰ cells/cm³ were successfully produced.