Low density microcellular foam processing in extrusion using CO₂

Abstract

Abstract A continuous extrusion process for the manufacture of low‐density microcellular polymers is presented. Microcellular polymers are foamed plastics characterized by a cell density greater than 10 9 cells/cm 3 and a fully grown cell size on the order of 10 μm. Previous research on continuous processing of microcellular polymers has focused on control of microcell nucleation in extrusion. This paper presents an effective means for control of cell growth to achieve a desired expansion ratio with CO 2 as a blowing agent in microcellular foam processing. Also, a strategy to prevent deterioration of the cell‐population density via cell coalescence during expansion is presented. Promotion of a desired volume expansion ratio and prevention of cell coalescence in microcellular foam processing were experimentally verified. By tailoring the extrusion processing parameters, microcellular HIPS foams with a cell density of 10 10 cells/cm 3 and a controlled expansion ratio in the range of 1.5 to 23 were obtained.