Development of Transparent Nanocellular Foams Using High-Pressure CO₂

Abstract

A new foaming apparatus, which can depressurize the vessel containing polymer sample and CO₂ from 100 MPa to atmospheric pressure in the order of milliseconds, was developed to generate a high degree of supersaturation. The effects of the high saturation pressure and rapid depressurization in polymer foaming process were studied using the apparatus with PMMA as a model polymer. Under the conditions studied, the cell nucleation density increased by more than an order of magnitude over the standard foaming process. Moreover, transparent nanocellular foams were obtained by combining the conditions and two-step foaming process.