SEARCH · Engineering Papers
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
A method for creating a three dimensional cross-linked polyimide structure includes dissolving a diamine, a dianhydride, and a triamine in a solvent, imidizing a polyamic acid gel by heating the gel, extracting the gel in a second solvent, supercritically drying the gel, and removing the solvent to create a polyimide aerogel.
Polyimide aerogels are a nanoporous material made by extracting the liquid portion of a wet gel and replacing it with air, while still maintaining the porous solid internal architecture. This results in a material with extremely low densities, low thermal conductivities, high internal surfaces areas, and low dielectric constants. Currently, complex aerogel forms are not possible, since they require molds in order to be shaped. To overcome this challenge, we are attempting to use various additive manufacturing techniques to produce complex architectures. Three different approaches are being studied to accomplish this. One is to print using a viscous wet gel and have the structure solidify at the end of the print, another is to use a mixing tip, where a less viscous gel and the final chemical that causes gelation will be mixed as it is printing, allowing it to gel layer by layer, and the third is to use a UV curable aerogel with a UV light following behind to solidify the gel as it prints. To have these approaches be successful, the printing parameters and the aerogel's chemical formulation need to be optimized. The more harmonious these two factors can be made, the more defined and complex the resulting structure can be. Preliminary results show that 3D printing polyimide aerogels are a viable option, but further optimization must occur for reliable printing.
RTM370 imide oligomer based on 2,3,3',4'-biphenyl dianhydride (a-BPDA), 3,4'-oxydianiline (3,4'-ODA) and terminated with the 4-phenylethynylphthalic (PEPA) endcap has been shown to exhibit a low melt viscosity (10-30 poise) at 280 C with a pot-life of 1-2 h and a high cured glass-transition temperature (Tg) of 370 C. RTM370 resin has been successfully infused into fiberglass-stitched T650-35 carbon-fabric preforms (ranged from 3- to 6-mm thick) by resin film infusion (RFI). The resulting composite panels were inspected by ultrasonic C-scan and by photomicrographs before and after post-curing as a quality control. Mechanical tests such as unnotched compression (UNC), open-hole compression (OHC), and short-beam shear strength (SBS) at ambient and elevated temperatures were performed before and after isothermal aging at 288 C for 1000 h to assess high-temperature performance. Thermal cycling of RTM370 stitched composites was also conducted from -54 C to 288 C for up to 1600 cycles to evaluate the microcrack resistance of RTM370 polyimide composites fabricated by RFI.
Aerogel Technologies has an exclusive license from NASA to commercialize polyimide aerogels developed at NASA GRC. They combine low density, low thermal conductivity, high specific strength, and soundproofing properties in a single material envelope. Aerogel Technologies and NASA GRC are working together to optimize the properties for lightweight, structural material for vibro-acoustic mitigation for launch vehicles, with the goal of achieving TRL 6 by the conclusion of the project.
RTM385-SLS is a melt-processable thermoset polyimide resin specially formulated with a complex melt viscosity (ƞ*) of ~104-105 poise for laser sintering. RTM385-SLS resin powder was mixed with 20-25% of hexagonal boron nitride (h-BN) and subjected to laser sintering (LS) to print out “Green” disks and dogbone specimens which could be further post-cured in an oven to complete the crosslinking of the reactive phenylethynyllphthalic anhydride (PEPA) terminal groups within the resin to achieve a very high glass transition temperature (T g ) of 385°C. The cured composite specimens were then subjected to thermal analysis, thermal conductivity measurement and mechanical testing for characterization.
Selective Laser Sintering (SLS) is an additive manufacturing technique that builds 3D models layer by layer using a laser to selectively melt cross sections in powdered polymeric materials, following sequential slices of the computer-aided design (CAD) model. SLS generally uses thermoplastic polymeric powders such as polyamides. The resultant 3D-printed objects are often weaker in their strength compared to traditionally processed materials, due to their higher porosity. This paper described the process development of using melt-processable imide oligomers terminated with reactive 4-phenylethynylphthalic anhydride (4-PEPA) to conduct laser sintering (LS). The first successful 3D-printing of high temperature RTM370 thermoset polyimide carbon fiber composites were further post-cured to promote additional crosslinking for achieving higher temperature (T g = 370°C) capability. Another novel imide oligomer, RTM385-SLS, formulated with a complex melt viscosity [ƞ*] of ~104-105 poise is also suitable for LS. RTM385-SLS resin powder was mixed with 20-25% of hexagonal boron nitride (h-BN) and subjected to LS to print out “Green” specimens which could be further post-cured to afford a thermally conductive but electrically insulating composites with high T g of 385 °C. The cured composite specimens were then subjected to mechanical testing, thermal conductivity and porosity measurements as well as SEM characterization.
Polymer adhesive laminates polyimide-film flat conductor cable. It is obtained by reacting an appropriate diamine with a dianhydride. The adhesive has also been used in the lamination of copper to copper for the preparation of multilayer circuit boards.
High temperature polyimide film and adhesive materials for spacecraft electrical equipment
Effects of 450 and 600 degrees F exposures on mechanical properties of glass-fiber polyimide resin sandwich panels to be used on large skin areas of SST aircraft
Effect of temperature, pressure, time on shear flexure strengths of polyimide-glass fiber laminates
Epoxy resin-coated polyimide plastic is used for bonding materials with different thermal coefficients in applications requiring precision mounting, especially where vibrations, temperature extremes, and low pressures are encountered. Low vapor pressure of the bonding material precludes outgassing problems.
Technique for manufacture of graphite composites uses high-char-forming processable polyimide resin systems to produce the graphitic matrix. Only three cyclic steps are required to yield a 99.7 percent graphite product.
With a cured polyimide resin content of less than about 20 percent by weight of the finished part, glass fabric laminates which have good structural properties and are self-extinguishing in a pure oxygen atmosphere can be prepared in the thickness range of 0.035 to 0.08 inch.
Development of high temperature polyimide rod seals for use with hydraulic fluids in advanced aircraft
Polyimides from some diaminoanthraquinones and pyromellitic dianhydride
High temperature polyimide actuator rod seals for aircraft hydraulic systems
Two types of polyimide seals are developed for hydraulic actuator rod in low pressure second stage of two-stage configuration. Each seal melts test objectives of twenty million cycles of operation at 534 K. Analytical and experimental study results are discussed. Potential applications are given.
Monomer solutions have high solubility and low solution viscosity. Since monomers are shipped in powder form and reaction to polyimide-acid prepolymer is omitted, the cost is low and handling is easy.