High temperature polyimide foams for aerospace vehicles

Due to a demand by the aerospace industry, NASA has begun developing the next generation of polyimide foams which will be utilized to reduce vehicle weight for the X-33 Program and Reusable Launch Vehicle (RLV) Program. The research activity at NASA Langley Research Center (LaRC) focuses on developing foam and foam structures which are made from a polyimide using monomeric solutions or salt solutions formed from the reaction of a dianhydride dissolved in a mixture of foaming agents and alkyl alcohols at room temperature. This process can produce polyimide foams with varying properties from a large number of monomers and monomer blends. The specific densities of these foams can range from 0.008 g/cc to 0.32 g/cc. Polyimide foams at densities 0.032 g/cc and 0.08 g/cc were tested for a wide range of physical properties. The foams demonstrated excellent thermal stability at 321°C, good thermal conductivity at 25°C of 0.0003 W/cm-K, compressive strengths as high as 0.84 MPa at 10% deflection, and a limiting oxygen index of 51%. Thermomechanical cyclic testing was also performed on these materials for 50 cycles at temperatures from -253°C to 204°C. The foams survived the cyclic testing without debonding or cracking.