Polyimide foams for aerospace vehicles

Due to a demand by the aerospace industry, NASA has begun developing the ne xt generation of polyimide foams which could be utilized to reduce vehicle weight for the X-33 and Reusable Launch Vehicle (RLV) programmes. The activ ity at NASA Langley Research Center focuses on developing polyimide foam an d foam structures which are made using monomeric solutions or salt solution s formed from the reaction of a dianhydride and diamine dissolved in a mixt ure of foaming agents and alkyl alcohols. This process can produce polyimid e 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(-1 ) to 0.32 g cc(-1). Polyimide foams at densities of 0.032 g cc(-1) and 0.08 g cc(-1) were teste d for a wide range of physical properties. The foams demonstrated excellent thermal stability at 321 degrees C, a good thermal conductivity at 25 degr ees C of 0.03 W m(-1) K-1, compressive strengths as high as 0.84 MPa at 10% deflection and a limiting oxygen index of 51%. Thermomechanical cyclic tes ting was also performed on these materials for 50 cycles at temperatures fr om -253 degrees C to 204 degrees C. The foams survived the cyclic testing w ithout debonding or cracking. Thermal forming of the 0.032 g cc(-1) foam wa s performed and a minimum radius curvature of 0.0711 m was achieved. The fo ams exhibited excellent properties overall and are shown to be viable for u se as cryogenic insulation on the next generation RLV.