Influence of supercritical fluid parameters on the polyimide aerogels in a high-efficiency supercritical drying process

A semi-continuous supercritical drying process was proposed to greatly improve the drying efficiency in producing polyimide aerogels . The influence of supercritical fluid parameters such as pressure and temperature on the aerogel properties were systematically investigated, based on the vapor-liquid equilibrium diagram of the ethanol-CO 2 binary system. Results showed supercritical drying efficiency was critical for the comprehensive properties of the aerogel, because solvent retention in the aerogel after drying could cause depressurization-induced shrinkage and a subsequent change in nano-structure in the vacuum drying that ensued. By continuous scCO 2 flushing at 90 °C and 16 MPa with the total drying time as short as 3 h, the aerogel showed a satisfactory shrinkage as low as 11.5%, a large specific surface area as high as 344.3 m 2 /g. Our findings also showed that the subcritical drying condition slightly below the critical mixture pressure of the binary system could provide special interest.