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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.

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At least 253 records · Page 14
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NASA NTRS1983

Search for selective ion diffusion through membranes

The diffusion rates of several ions through some membranes developed as battery separators were measured. The ions investigated were Li(+), Rb(+), Cl(-), and So4. The members were crosslinked polyvinyl alcohol, crosslinked polyacrylic acid, a copolymer of the two, crosslinked calcium polyacrylate, cellulose, and several microporous polyphenylene oxide based films. No true specificity for diffusion of any of these ions was found for any of the membranes. But the calcium polyacrylate membrane was found to exhibit ion exchange with the diffusing ions giving rise to the leaching of the calcium ion and low reproducibility. These findings contrast earlier work where the calcium polyacrylate membrane did show specificity to the diffusion of the copper ion. In general, Fick's law appeared to be obeyed. Except for the microporous membranes, the coefficients for ion diffusion through the membranes were comparable with their values in water. For the microporous membranes, the values found for the coefficients were much less, due to the tortuosity of the micropores.

May, C. E.↗
NASA NTRS1983

Polymers in solar energy utilization

A laser photoacoustic technique (LPAT) has been verified for performing accelerated life testing of outdoor photooxidation of polymeric materials used in solar energy applications. Samples of the material under test are placed in a chamber with a sensitive microphone, then exposed to chopped laser radiation. The sample absorbs the light and converts it to heat by a nonradiative deexcitation process, thereby reducing pressure fluctuations within the cell. The acoustic signal detected by the microphone is directly proportional to the amount of light absorbed by the specimen. Tests were performed with samples of ethylene/methylacrylate copolymer (EMA) reprecipitated from hot cyclohexane, compressed, and molded into thin (25-50 microns) films. The films were exposed outdoors and sampled by LPAT weekly. The linearity of the light absorbed with respect to the acoustic signal was verified.Correlations were established between the photoacoustic behavior of the materials aged outdoors and the same kinds of samples cooled and heated in a controlled environment reactor. The reactor tests were validated for predicting outdoor exosures up to 55 days.

Liang, R. H.↗
NASA NTRS1985

Elastomeric Cathode Binder

Soluble copolymer binder mixed with cathode material and solvent forms flexible porous cathode used in lithium and Ni/Cd batteries. Cathodes prepared by this process have lower density due to expanding rubbery binder and greater flexibility than conventional cathodes. Fabrication procedure readily adaptable to scaled-up processes.

Yen, S. P. S.↗
NASA NTRS1983

Plasma polymerized high energy density dielectric films for capacitors

High energy density polymeric dielectric films were prepared by plasma polymerization of a variety of gaseous monomers. This technique gives thin, reproducible, pinhole free, conformable, adherent, and insoluble coatings and overcomes the processing problems found in the preparation of thin films with bulk polymers. Thus, devices are prepared completely in a vacuum environment. The plasma polymerized films prepared all showed dielectric strengths of greater than 1000 kV/cm and in some cases values of greater than 4000 kV/cm were observed. The dielectric loss of all films was generally less than 1% at frequencies below 10 kHz, but this value increased at higher frequencies. All films were self healing. The dielectric strength was a function of the polymerization technique, whereas the dielectric constant varied with the structure of the starting material. Because of the thin films used (thickness in the submicron range) surface smoothness of the metal electrodes was found to be critical in obtaining high dielectric strengths. High dielectric strength graft copolymers were also prepared. Plasma polymerized ethane was found to be thermally stable up to 150 C in the presence of air and 250 C in the absence of air. No glass transitions were observed for this material.

Yamagishi, F. G.↗
NASA NTRS1979

Manufacture of DPFC-DMS polymer in the SKG range

BPFC-DMS block copolymers were synthesized on a pre-pilot scale (i.e., to 5 Kg lots) and subsequently fabricated into clear, colorless films. Details of the synthesis procedures, property determinations, and film casting techniques are presented. Solubility, viscosity and molecular weight characteristics of the resulting product are reported.

Hughes, B. M.↗
NASA NTRS1983

Towards an organic photobattery - Photovoltaic properties of some thermal copolyamino acids

Thermal copolymers of amino acids have been examined as a novel material for photovoltaic devices. Due to the steric effects of amino acids during polymerization, these polymers are highly ordered, and pigments such as flavins and pterins are formed as part of the polymer. The controllably varied composition of the amino acids in the polymer makes it possible to get either electron-donor or electron-acceptor, or both kinds of groups in varying degrees. The constituent photosensitive element has been made either of photosensitive polymer film or spherule.

Przybylski, A. T.↗
NASA NTRS1986

Solvent-Resistant, Thermally Stable Poly(Carbonate-Imides)

New polymers and copolymers based on polyimide backbone with carbonate moieties exhibit high temperature capability. Because of carbonate unit, many of these materials also exhibit high order or crystallinity. All of new imidecontaining polymers insensitive to acetone. New poly (carbonate-imide) exhibits significantly increased temperature resistance and shows less sensitivity to solvents than commercial polycarbonates.

St. Clair, T. L.↗
NASA NTRS1984

The Effect of Cross-Link Density on the Toughening Mechanism of Elastomer-Modified Epoxies

A DGEBA epoxide resin (EPON 828) was elastomer modified by using three different carboxyl terminated butadiene acrylonitrile copolymers. The fracture toughness of these elastomer modified epoxies was measured in terms of the critical strain energy release rate, G sub IC. The toughening mechanism was elucidated using a tensile dilatometry technique. A plot of volume strain versus longitudinal strain often reveals the types of micromechanical deformations occurring in the uniaxial tensile specimen up to yield. Several microscopy techniques were employed to corroborate the tensile dilatometry results. The role of matrix ductility on the toughening mechanism of elastomer modified epoxies was investigated. By reducing the cross link density with various equivalent weight epoxide resins. Fracture toughness was again measured in terms of G sub IC. The characterization of the toughening mechanism was performed using a uniaxial tensile dilatometry technique and corroborated using various microscopy techniques.

Pearson, R. A.↗
NASA NTRS1985

Synthesis and Characterization of Copolyimides with Varying Flexibilizing Groups

A series of polyimides and copolyimides with varying flexibilizing groups in their backbone were prepared. They were characterized in order to evaluate the effect of these groups on their rheological, mechanical, adhesive, and thermal properties. A copolymer with equimolar amounts of m-PDA and 4,4'-ODA exhibited the lowest viscosity at all strain rates studied. Since this particular polymer exhibited the best flow properties, it was also evaluated as an adhesive and was found to have exceptional characteristics for this application.

Burks, H. D.↗
NASA NTRS1984

Phosphorus-containing imide resins - Modification by elastomers

The syntheses and general features of addition-type maleimide resins based on bis(m-aminophenyl)phosphine oxide and tris(m-aminophenyl)phosphine oxide have been reported previously. These resins have been used to fabricate graphite cloth laminates having excellent flame resistance. These composites did not burn even in pure oxygen. However, these resins were somewhat brittle. This paper reports the modification of these phosphorus-containing resins by an amine-terminated butadiene-acrylonitrile copolymer (ATBN) and a perfluoroalkylene diaromatic amine elastomer (3F). An approximately two-fold increase in short beam shear strength and flexural strength was observed at 7 percent ATBN concentration. The tensile, flexural, and shear strengths were reduced when 18 percent ATBN was used. Anaerobic char yields of the resins at 800 C and the limiting oxygen indexes of the laminates decreased with increasing ATBN concentration. The perfluorodiamine (3F) was used with both imide resins at 6.4 percent concentration. The shear strength was doubled in the case of the bisimide with no loss of flammability characteristics. The modified trisimide laminate also had improved properties over the unmodified one. The dynamic mechanical analysis of a four-ply laminate indicated a glass transition temperature above 300 C. Scanning electron micrographs of the ATBN modified imide resins were also recorded.

Varma, I. K.↗
NASA NTRS1984

Impact properties of rubber-modified epoxy resin-graphite-fiber composites

To improve the impact resistance of graphite-fiber composites, a commercial and an experimental epoxy resin were modified with liquid reactive rubber and a brominated epoxy resin. The commercial epoxy was a tetrafunctional resin, and the experimental epoxy was a trifunctional resin. The reactive rubber was a carboxyl-terminated butadiene-acrylonitrile copolymer. The rubber content was varied from 0 to 25 percent (wt). The brominated epoxy resin was used at Br levels of 4, 19, and 35 percent of the resin. Composites were prepared with woven graphite cloth reinforcement. The composites were evaluated by using flexural strength in the dry state and an elevated temperature after saturation with water. The impact properties were determined by measuring shear strength after falling-ball impact and instrumented impact. The rubber-modified, trifunctional resin exhibited better properties, when tested in hot-wet conditions in a heated oven at 366 K (after boiling the material for 2 h in demineralized water), than the tetrafunctional resin. Improved impact resistance was observed with the addition of the reactive rubber to the epoxy resin. Further improvement was observed with the addition of the brominated epoxy resin.

Gilwee, W. J.↗
NASA NTRS1985

Synthesis and properties of copoly(carbonate imides)

Copoly(carbonate imides) with varying amounts of carbonate in the backbone were prepared by reacting 4,4-prime-diaminodiphenyl carbonate and 4,4-prime diaminodiphenyl ether with benzophenonetetracarboxylic acid dianhydride in dimethylacetamide at room temeprature. Homopolymers of the two diamines as well as of 3,4-prime- and 3,3-prime-diaminodiphenyl carbonate were prepared in a similar procedure and their properties compared with those of the copolymers.

Maudgal, S.↗
NASA NTRS1986

Fire-Resistant Polyimides Containing Phosphorus

Limiting oxygen index increased. Copolyimide with a group containing phosphorus synthesized from 1-2,4-diaminobenzene, m-phenylenediamine, and tetracarboxylic dianhydride. Copolymer more fire resistant than corresponding polyimide without phosphorus.

Mikroyannidis, J.↗
NASA NTRS1985

Toughening reinforced epoxy composites with brominated polymeric additives

Cured polyfunctional epoxy resins including tris (hydroxyphenyl) methane triglycidyl ether are toughened by addition of polybrominated polymeric additives having an EE below 1500 to the pre-cure composition. Carboxy terminated butadiene acrylonitrile rubber is optionally present in the precure mixture as such or as a pre-formed copolymer with other reactants. Reinforced composites, particularly carbon reinforced composites, of these resins are disclosed and shown to have improved toughness.

Nir, Z.↗
NASA NTRS1985

Toughening reinforced epoxy composites with brominated polymeric additives

Cured polyfunctional epoxy resins including tris(hydroxyphenyl)methane triglycidyl ether are toughened by addition of polybrominated polymeric additives having an EE below 1500 to the pre-cure composition. Carboxy-terminated butadiene-acrylonitrile rubber is optionally present in the pre-cure mixture as such or as a pre-formed copolymer with other reactants. Reinforced composites, particularly carbon-reinforced composites, of these resins are disclosed and shown to have improved toughness.

Nir, Z.↗
NASA NTRS1986

Light weight fire resistant graphite composites

Composite structures with a honeycomb core and characterized by lightweight and excellent fire resistance are provided. These sandwich structures employ facesheets made up of bismaleimide-vinyl styrylpyridine copolymers with fiber reinforcement such as carbon fiber reinforcement. In preferred embodiments the facesheets are over layered with a decorative film. The properties of these composites make them attractive materials of construction aircraft and spacecraft.

Kourtides, D. A.↗
NASA NTRS1986

Polyarylene Ethers with Improved Properties

This invention relates to novel polyarylene ethers which possess the combination of high strength, toughness, and high use temperature with ease of extrusion and formation into complex objects. These polyarylene ethers are suitable for use in adhesives, coatings, films, membranes, and composite matrices. The polyarylene ethers of this invention are the polycondensation products from the reaction of either 1,3-bis (4-chloro or fluorobenzoyl) benzene with any one of the following bisphenolic compounds: bis (3-hydroxyphenyl) methane; bis (4-hydroxyphenyl) methane; 1,1-dimethyl-bis (4-hydroxyphenyl)methane, or 9,9-bis (4-hydroxyphenyl) fluorene. Random and block copolymers are also comprehended.

Hergenrother, P. M.↗