Abstract: A method of forming complex polyimide foam shapes by impregnating a low density, open cell, reticulated foam with polyimide foam precursor, placing the combination in a mold, closing the mold, then heating the assembly to the foaming and curing temperatures of the precursor. As the powdered precursor expands, it spreads throughout the reticulated foam producing a product having substantially uniform density and polyimide foam characteristics. If desired, the reticulated foam can be removed from the product by using a material that outgasses and boils away at polyimide processing temperatures. Radar absorbing materials may be incorporated in the reticulated foam so that the final product will have uniformly distributed radar absorbing components with the desirable high temperature resistance and other properties of polyimide foams.

Abstract: A method of manufacturing polyimide foam filled structures such as honeycomb panels. A polyimide foam precursor is prepared in powder form. A layer of the powder is heated and foamed at the resin condensation temperature and pre-cured to an easily handleable, stiff and inflexible state. A multi-cell, thin-walled structure having open cells along a surface is pressed into and through the foam sheet so that foam pieces fill the cells. The foam is then heated to a final cure temperature at which the foam becomes stable, resilient and flexible. Face sheets may be bonded to the structure to retain the foam pieces in the cells. If desired, the walls of the structure that contact the foam may be coated with an adhesive, such as a liquid polyimide adhesive resin precursor, so that the foam will be bonded to the cell walls when the liquid resin precursor is cured as a necessary result of the final foam cure conditions.

Abstract: A method of forming complex polyimide foam shapes by impregnating a low density, open cell, reticulated form with polymide foam precursor, placing the combination in a mold, closing the mold, then heating the assembly to the foaming and curing temperatures of the precursor. As the powdered precursor expands, it spreads throughout the reticulated foam producing a product having substantially uniform density and polyimide foam characteristics. If desired, the reticulated foam can be removed from the product by using a material that outgasses and boils away at polyimide processing temperatures. Radar absorbing materials may be incorporated in the reticulated foam so that the final product will have uniformly distributed radar absorbing components with the desirable high temperature resistance and other properties of polyimide foams.

Abstract: A method of improving the flame resistance of foams, such as open cell polyimide foams, through the introduction of finely divided non-metallic inorganic particles which are gel forming and insoluble in water and polar organic liquids into the foam cells. A stable liquid suspension or gel, preferably aqueous is prepared using these particles. An opacifier such as finely divided titanium dioxide or tin oxide may also be added. An open cell foam product is placed in the gel until the cells fill with the gel. Excess gel is removed and the foam is dried, leaving the particles trapped in the cells. If desired, the foam may be post treated, such as by compression at the stabilizing temperature, resulting in a densified foam which further mechanically traps the particles and further improves the flame resistance.

Abstract: A method of improving the flame resistance of foams, such as open cell polyimide foams, through the introduction of finely divided non-metallic inorganic particles which are gel forming and insoluble in water and polar organic liquids into the foam cells. A stable liquid suspension or gel, preferably aqueous is prepared using these particles. An opacifier such as finely divided titanium dioxide or tin oxide may also be added. An open cell foam product is placed in the gel until the cells fill with the gel. Excess gel is removed and the foam is dried, leaving the particles trapped in the cells. If desired, the foam may be post treated, such as by compression at the stabilizing temperature, resulting in a densified foam which further mechanically traps the particles and further improves the flame resistance.

Abstract: A method of improving the flame resistance of foams, such as open cell polyimide foams, through the introduction of finely divided non-metallic inorganic particles which are gel forming and insoluble in water and polar organic liquids into the foam cells. A stable liquid suspension or gel, preferably aqueous is prepared using these particles. An opacifier such as finely divided titanium dioxide or tin oxide may also be added. An open cell foam product is placed in the gel until the cells fill with the gel. Excess gel is removed and the foam is dried, leaving the particles trapped in the cells. If desired, the foam may be post treated, such as by compression at the stabilizing temperature, resulting in a densified foam which further mechanically traps the particles and further improves the flame resistance.