Synergetic effect between curing reaction and CO2 diffusion for microcellular epoxy foam preparation in supercritical CO2

Directly rapid depressurization foaming process has been successfully applied to prepare microcellular epoxy foams using supercritical CO2 as blowing agent. It is found that both curing reaction and CO2 diffusion are crucial for controlling cell morphology. For epoxy of tetraglycidyl-4,4′-diaminodiphenyl-methane (TGDDM) and 4,4-diaminodiphenylsulfone (4,4-DDS) system, the experimental and molecular simulation results displayed that higher CO2 pressure always promotes curing reaction, and CO2 diffusion is more sensitive to pressure at low curing degree, while limited by high curing degree. The foaming experimental results showed that there existed a suitable curing degree range, in which both unsaturated CO2 concentration and curing degree contribute to good cell structure. Higher CO2 pressure can broaden this foamable window. The microcellular epoxy foam with an average cell diameter of 14.6 µm and cell density over 109 cells/cm3 as well as volume expansion ratio of 14.5 has been obtained at 85% curing degree under 22 MPa CO2 pressure.