Ultrasound and H2O assisted scCO2 foaming technology for preparation of PS/PMMA composite foams with ultra-lightweight and super thermal-insulation

Porous polymer with lower density is more favorable for practical thermal insulation. In this work, a judicious combination of mechanical mixing and supercritical carbon dioxide foaming was applied to prepare ultra-lightweight polymer microcellular foam. The polymer foaming behavior is improved by adding water and ultrasound as an external energy source. The presence of water greatly increases the efficiency of ultrasound propagation, resulting in an almost two-fold increase in expansion ratio of foams. With the assistance of water and ultrasonic irradiation, the prepared foams have a 79-fold foaming expansion ratio and an average thermal conductivity as low as 26.79 mW/mK. The ultrasound also affects the process of foaming in both the saturation and release stage, but is more effective in the release stage than in the saturation stage. Consequently, this study provides a novel, facile, versatile, green approach for the preparation of microcellular polymers with ultra-lightweight and super thermal insulation.