Pyrolysis behavior, kinetics, and mechanism of polyimide aerogels

Polyimide aerogels (PIAs) have extensive application prospects in numerous fields for their appealing characteristics, including low density, superior thermal stability, high flexibility, and remarkable mechanical properties. However, the thermal safety of polyimide aerogels in practical applications has been neglected, the pyrolysis behaviors and reaction kinetics need to be clarified. In this work, PIAs with different repeat units from 10 to 60 were prepared using the sol-gel method, and the effect of repeat unit on the basic properties, microstructure, and thermal stability of polyimide aerogel was studied. The PIAs with a repeat unit of 40 have the lowest density, thermal conductivity, radial shrinkage, the highest porosity, the largest specific areas, and so on. Furthermore, the pyrolysis process and products of PIA were analyzed by TG-FTIR-MS. The pyrolysis kinetic parameters were calculated by model-free method and the predicted reaction model was chosen by CR and Malek method. The calculated kinetic parameters are in good agreement with the experimental data at different heating rates, which can guide the pyrolysis behavior and thermal safety of polyimide aerogels.