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At least 91 records · Page 5

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NASA NTRS1971

Materials for foam type insulation

An internal foam fabrication is one of the concepts being considered for cryogenic insulation on the hydrogen tanks of the shuttle vehicle. The three-dimensional polyurethane used on the S-4 B tanks failed to meet the higher temperature requirements of the shuttle vehicle, however, and other foams under consideration include polyisocyanurates, polyphenylene oxides, polyimides, and polybenzimidazoles. Improved adhesive systems for attaching the foams to the interior tank wall are under study.

Hill, W. E.↗

NASA NTRS1971

Development of flame resistant metal and metal-glass blended structures

A description is given of the design and fabrication of candidate flame-resistant woven and knitted fabrics, tapes, webbings, and cords as replacements for those items used in the Apollo spacecraft which were previously made of nylon and polyester. Structures made from Chromel R metal fibers (74% Ni, 20% Cr, 2-1/2% Fe, 2-1/2% Al, 1/2% Si, 1/2% Mo), Beta glass fibers and high-temperature organic fibers such as PBI (polybenzimidazole) were developed and evaluated. The feasibility of improving the performance of selected fabrics by using CNR (carboxy nitroso rubber) or other nonflammable coatings were also investigated.

Coskren, R. J.↗

NASA NTRS1971

Composite seals for liquid hydrogen and nuclear radiation environments.

Description of plastic composite seals for service in a liquid-hydrogen and nuclear-radiation environment. The radiation-resistant aromatic heterocyclic class of polymers, including polyimide, polybenzimidazole, and polyquinoxaline, were evaluated for this application. The seal developed is based on a design involving a resin-starved laminate consisting of alternating layers of woven glass fabric and polymer film. This design imparts a mechanical spring characteristic to the seal, resulting in essentially complete elastic recovery when unloaded, and eliminates cold flow. Encapsulating techniques employing the polyquinoxaline polymer were developed which rendered the seal impervious to liquid hydrogen. The seals were tested before and after gamma irradiation up to 10 to the 10th ergs/g. Load/deflection and leakage tests were performed over a temperature range from -423 through +500 F.

Van Auken, R. L.↗

NASA NTRS1972

Flame retardant treatments of PBI fabric.

Fabrics knitted or woven from polybenzimidazole (PBI) fibers were treated to reduce flammability in oxygen atmospheres, particularly that of 5 psia oxygen. Bromination to approximately 15% weight gain of such fabrics led to markedly lower burning rates; samples brominated to over 80% weight gain were self-extinguishing in 5 psia oxygen. The loss in tensile strength of fabrics due to bromination was negligible although shrinkage was observed. Free fibers showed negligible losses on bromination. Treatment of PBI fabric with organophosphorus compounds also achieved self-extinguishing character in 5 psia oxygen but the enhanced flameproofing was largely lost on leaching. Reaction with POCl3 in pyridine led to a permanent reduction in flammability.

Temin, S. C.↗

NASA NTRS1972

NERVA turbopump bearing retainer fabrication on nonmetallic retainer

The need for a low-wear, lightweight, high strength bearing retainer material with a radiation degradation threshold of 10 to the 9th power rads (C) prompted development of nonmetallic reinforced polymers of the following types: (1) polybenzimidazole, (2) polyimide, and (3) polyquinoxaline. Retainers were machined from tubular laminates (billets), including reinforcement by either glass or graphite fabric or filament. Fabrication of billets involves hot preimpregnation of the reinforcement fabric or filament with polymer followed by wrapping this prepreg over a heated mandrel to form a tube with the required thickness and length.

Accinelli, J. B.↗

NASA NTRS1973

Evaluation of 165 deg F reverse osmosis modules for washwater purification.

Three membrane systems have been evaluated for concentration at 165 F of wash-water contaminants. Membranes tested are polybenzimidazole (hollow fibers), cellulose acetate blend (spiral wound), and sulfonated polyphenylene oxide (plate-and-frame). Detailed membrane flux and rejection data are presented for 200-hr life tests with synthetic wash water, at two concentrations, and real wash water, at one concentration. Advantages and limitations of the membrane configurations, are discussed.

Hossain, S.↗

NASA NTRS1974

Cryogenic/high temperature structural adhesives

Results are described of the work performed to develop a structural adhesive system which possesses useful properties over a 20K (-423 F) to 589 K (600 F) temperature range. Adhesives systems based on polyimide, polyphenylquinoxaline polyquinoxaline, polybenzothiazole and polybenzimidazole polymers first were screened for suitability. Detailed evaluation of two polyimide adhesive sytems, Br34/FM34 and P4/A5F or P4A/A5FA, and one polyphenylquinoxaline adhesive system, PPQ II (IMW), then was performed. Property information was generated over the full temperature range for shear strength, stressed and unstressed thermal aging, thermal shock and coefficient of thermal expansion. Both polyimide adhesive systems were identified as being capable of providing structural adhesive joints for cryogenic/high temperature service.

Vaughan, R. W.↗

NASA NTRS1974

Cryogenic/high temperature structural adhesives

Studies were conducted to develop a structural adhesive system possessing useful properties over a 20 to 589 K temperature range. Adhesive systems based on polyimide, polyphenylquinoxaline, polyquinoxaline, polybenzothiazole and polybenzimidazole polymers first were screened for suitability. Detailed evaluation of two polyimide adhesive systems, BR34/FM34 and P4/A5F or P4A/A5FA, and one polyphenylquinoxaline adhesive system, PPQ (IMW), then was performed. Property information was generated over the full temperature range for shear strength, stressed and unstressed thermal aging, thermal shock, and coefficient of thermal expansion. Both polyimide adhesive systems were identified as being capable of providing structural adhesive joints for cryogenic/high temperature service.

Vaughan, R. W.↗

NASA NTRS1974

Preparation for foam composites

Methods were developed for the fabrication of fire resistant panels utilizing polybenzimidazole (PBI) and Kerimid 601 resins along with glass, quartz, and Kevlar reinforcements. Stitched truss structure, both unfilled and filled with PBI foam, were successfully fabricated and tested. Second generation structures were then selected, fabricated, and tested, with a PBI/glass skin/PBI foam sandwich structure emerging as the optimum panel concept. Mechanical properties, smoke generation, and fire resistance were determined for the candidate panels.

Maximovich, M. G.↗

NASA NTRS1976

Non-flammable elastomeric fiber from a fluorinated elastomer and containing an halogenated flame retardant

Flame retardant elastomeric compositions are described comprised of either spandex type polyurethane having incorporated into the polymer chain halogen containing polyols, conventional spandex type polyurethanes in physical admixture with flame retardant additives, or fluoroelastomeric resins in physical admixture with flame retardant additives. Methods are described for preparing fibers of the flame retardant elastomeric materials and articles of manufacture comprised of the flame retardant clastomeric materials and non elastic materials such as polybenzimidazoles, fiberglass, nylons, etc.

Howarth, J. T.↗

NASA NTRS1976

The sensitivity of relative toxicity rankings by the USF/NASA test method to some test variables

Pyrolysis temperature and the distance between the source and sensor of effluents are two important variables in tests for relative toxicity. Modifications of the USF/NASA toxicity screening test method to increase the upper temperature limit of pyrolysis, reduce the distance between the sample and the test animals, and increase the chamber volume available for animal occupancy, did not significantly alter rankings of relative toxicity of four representative materials. The changes rendered some differences no longer significant, but did not reverse any rankings. The materials studied were cotton, wool, aromatic polyamide, and polybenzimidazole.

Hilado, C. J.↗

NASA NTRS1977

Thermochemical characterization of polymers for improved fire safety

Apparatus has been constructed for studying the thermal decomposition of polymers as a function of temperature. Such data is needed to evaluate the toxic threat presented by polymeric materials under fire conditions such as the smoldering fire of the type that occurs in closed areas such as coat closets in which anaerobic decomposition of polymers occurs. The apparatus allows the products of thermal decomposition to be collected and analyzed by infrared spectrometry and mass spectrometry. Data obtained from dog hair, an aromatic polyamide, polyphenylene sulfide, and polybenzimidazole are presented. It was found that significant amounts of toxic gas were evolved from dog hair at temperatures as low as 250 C, while temperatures in excess of 500 C were necessary in order for the evolution of toxic gas from the aromatic polymers to become significant.

Lerner, N. R.↗

NASA NTRS1979

Ultrafine PBI fibers and yarns

Gentle precisely controlled process is used to draw polybenzimidazole (PBI) fibers to denier as low as 0.17 per fiber. Yarns of lightweight fibers could be useful in applications where lightweight textiles must withstand high temperatures, corrosion, or radiation.

Leal, J. R.↗

NASA NTRS1978

Process for spinning flame retardant elastomeric compositions

Flame retardant elastomeric compositions comprised of either spandex type polyurethane having halogen containing polyols incorporated into the polymer chain, conventional spandex type polyurethanes in physical admixture with flame retardant additives, or fluoroelastomeric resins in physical admixture with flame retardant additives were developed. Methods are described for preparing fibers of the flame retardant elastomeric materials and manufactured articles as well as nonelastic materials such as polybenzimidazoles, fiberglass, and nylons, for high oxygen environments.

Howarth, J. T.↗

NASA NTRS1978

Ultrathin metallized PBI paper

A study to determine the feasibility of preparing ultrathin papers with a target weight of 3.5 g/m squared from polybenzimidazole (PBI) fibrids was undertaken. Small hand sheets of target weight were fabricated. They were light brown, low density materials with sufficient strength to be readily handleable. Characterization of these sheets included strength, fold endurance, thermal gravimetric analysis in air and nitrogen and photomicrographs. Two different batches of PBI fibrids were studied and differences in fabrication performance were noted. In neither case could target weight papers be prepared using conventional paper making techniques.

Chenevey, E. C.↗

NASA NTRS1980

Status of high-temperature laminating resins and adhesives

High-temperature polymers now being developed as adhesives and composite matrices are reviewed, including aromatic polyimides, polybenzimidazoles, polyphenylquinoxalines, nadic end-capped imide oligomers, maleimide end-capped oligomers, and acetylene-terminated imide oligomers. The mechanical properties of laminates based on these resins are reported together with preliminary test results on the adhesive properties for titanium-to-titanium and composite-to-composite lap shear specimens.

Hergenrother, P. M.↗

NASA NTRS1983

Fire resistant films for aircraft applications

Alternative sandwich panel decorative films were investigated as replacements for the polyvinyl fluoride currently used in aircraft interiors. Candidate films were studied for flammability, smoke emission, toxic gas emission, flame spread, and suitability as a printing surface for the decorative acrylic ink system. Several of the candidate films tested were flame modified polyvinyl fluoride, polyvinylidene fluoride, polyimide, polyamide, polysulfone, polyphenylsulfone, polyethersulfone, polybenzimidazole, polycarbonate, polyparabanic acid, polyphosphazene, polyetheretherketon, and polyester. The films were evaluated as pure films only, films silk-screened with an acrylic ink, and films adhered to a phenolic fiberglass substrate. Films which exhibited the highest fire resistant properties included PEEK polyetheretherketon, Aramid polyamide, and ISO-BPE polyester.

Kourtides, D. A.↗

NASA NTRS1983

Fire resistant films for aircraft applications

Kourtides, D. A.↗