Functionally Graded Polyimide Nanocomposite Foams

 

Abstract

The objective of the research is to develop functionally graded polyimide foams as light-weight, high performance thermal protection systems (TPS) for ablative and inflatable/flexible/deplorable structures used in space exploration missions. Graded polyimide foams will be fabricated with density gradient using melt processable thermoplastic polyimide films by a solid state foaming process with supercritical CO2. Gradient polyimide foam structures with tuned thermal protection properties are unique and not available until now. The advantage of this innovative approach is two folds:

• Functionally graded, non-homogeneous polyimide foams that allows continuous variation in macroscopic mechanical and physical properties, to tune the thermal conductivity, specific heat, density, and ablative behavior;
• The use of melt processable polyimides and the solid state supercritical CO2 foaming process eliminates the needs of using high boiling solvents, and the costly, tedious solvent exchange required during the supercritical CO2 drying to make porous aerogels from solution.

Open-celled polyimide foams with large visible uniform pore sizes have been produced commercially, however, graded porous polyimide thin films with density gradient, open- or closed-cell, are rare and pose more technical challenges, but can provide additional unique benefits.