Polyimide-Foam/Aerogel Compositesfor Thermal InsulationComposites of specific types of polymerfoams and aerogel particles or blanketshave been proposed to obtain thermalinsulation performance superior to thoseof the neat polyimide foams.These composites have potential to alsoprovide enhanced properties for vibrationdampening or acoustic attenuation.The specific type of polymer foam isdenoted "TEEK-H," signifying a series,denoted "H," within a family of polyimidefoams that were developed at NASA'sLangley Research Center and arecollectively denoted "TEEK" (an acronymof the inventors' names).The specific types of aerogels includeNanogel® aerogel particles from CabotCorporation in Billerica, MA. and ofSpaceloft® aerogel blanket from AspenAerogels in Northborough, MA.The composites are inherently flame-retardantand exceptionally thermally stable.Because of thermal cycling, aging, andweathering most polymer foams do not performwell at cryogenic temperatures and willundergo further cracking over time.The TEEK polyimides are among the fewexceptions to this pattern, and the proposedcomposites are intended to have all thedesirable properties of TEEK-H foams, plusimproved thermal performance along withenhanced vibration or acoustic-attenuationperformance.A composite panel as proposed would befabricated by adding an appropriate amountof TEEK friable balloons into a mold toform a bottom layer. A piece of flexibleaerogel blanket material, cut to the desiredsize and shape, would then be placed onthe bottom TEEK layer and sandwichedbetween another top layer of polyimide friableballoons so that the aerogel blanket wouldbecome completely encased in an outer layerof TEEK friable balloons. Optionally, theprocess could be further repeated to producemultiple aerogel-blanket layers interspersedwith and encased by TEEK friable balloons.The sandwiching of aerogel bulk-fill particleswould follow the same methodology or couldbe mixed directly with friable balloons upto 40% weight loading of the aerogel particlesto friable balloons. After sandwiching ormixing of the polymide and aerogel components,the mold, without a top cover, would beplaced in a convection furnace and heated ata temperature of 250 °C for one hour.Then the top cover would be placed on the moldand the temperature increased to about 320 °Cfor between 1 and 3 hours for full imidizationof the polyimide component.The resulting composite should have all thedesirable properties of TEEK, and its effectivethermal conductivity should be less than thatof an approximately equally dense panel madeof TEEK foam only. The heat transfer reductionis directly proportional to % loading of theaerogel component. The excellent structuralintegrity of the foam material is maintainedin the composite formulations.~ Full Article @Nasa Tech Briefs
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