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At least 541 records · Page 30

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NASA NTRS1976

Thermoplastic polymers for improved fire safety

The thermochemical and flammability characteristics of some typical thermoplastic materials currently in use and others being considered for use in aircraft interiors are described. The properties studied included (1) thermomechanical properties such as glass transition and melt temperature, (2) changes in polymer enthalpy by differential scanning calorimetry, (3) thermogravimetric analysis in anaerobic and oxidative environments, (4) oxygen index, (5) smoke evolution, (6) relative toxicity of the volatile products of pyrolysis, and (7) selected physical properties. The generic polymers that were evaluated included: acrylonitrile butadiene styrene, bisphenol A polycarbonate, 9,9 bis (4-hydroxyphenyl) fluorene polycarbonatepoly (dimethyl siloxane) block polymer, phenolphthalein bisphenol A polycarbonate, phenolphthalein polycarbonate, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, polyaryl sulfone, chlorinated polyvinyl chloride homopolymer, polyvinyl fluoride, and polyvinylidene fluoride. Processing parameters, including molding characteristics of some of the advanced polymers, are described. Test results and relative ranking of some of the flammability, smoke, and toxicity properties are presented.

Kourtides, D. A.↗

NASA NTRS1977

Lubricant rheology applied to elastohydrodynamic lubrication

Viscosity measurements in a high pressure rheometer, elastohydrodynamic simulator studies (including the development of a temperature measuring technique), and analytical fluid modeling for elastohydrodynamic contacts are described. The more recent research which is described concerns infrared temperature measurements in elastohydrodynamic contacts and the exploration of the glassy state of lubricants. A correlation, of engineering significance, was made between transient surface temperature measurements and surface roughness profiles. Measurements of glass transitions of lubricants and the study of the effect of rate processes on materials lead to the conclusion that typical lubricants go into the glassy state as they pass through the contact region of typical elastohydrodynamic contacts.

Winer, W. O.↗

NASA NTRS1976

New aromatic silicon-containing polyamides

The experiments described were aimed at studying systematically the effect of silyl linkages on the thermogravimetric and thermomechanical properties of aromatic polyamides. Specifically, 18 aromatic silicon-containing polyamides were synthesized via interfacial polymerization of six silicon-containing diacid chlorides with 3,3-prime-diaminodiphenylmethane, 3,3-prime-diaminobenzophenone, and 1-(3-prime-aminobenzyl)-4-(3-double prime-aminobenzoyl)benzene. All polyamides were soluble in m-cresol and N,N-dimethylacetamide, and had glass transition temperatures between 178 and 254 C. Thermogravimetric analysis conducted in static air on film specimens showed 5 and 10 percent weight losses between 331 and 400 C and 354 and 440 C, respectively. The potential gain in processability engendered by incorporation of silane substituents was offset in most cases by substantial losses in thermo-oxidative stability.

Pratt, J. R.↗

NASA NTRS1977

Thermochemical characterization of some thermoplastic materials

The thermochemical and flammability characteristics of some typical thermoplastic materials currently in use or being considered for use in aircraft interiors are described. The properties studied included thermomechanical properties such as glass-transition and melt temperature, changes in polymer enthalpy, thermogravimetric analysis in anerobic and oxidative environments, oxygen index, smoke evolution, relative toxicity of the volatile products of pyrolysis, and selected physical properties. The generic polymers evaluated included acrylonitrile butadiene styrene, bisphenol A polycarbonate, 9,9 bis (4-hydroxyphenyl) fluorene polycarbonate-poly (dimethylsiloxane) block polymer, phenolphthalein-bisphenol A polycarbonate, phenolphthalein polycarbonate, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, polyaryl sulfone, chlorinated polyvinyl chloride homopolymer, polyvinyl fluoride, and polyvinylidene fluoride. Processing parameters, including molding characteristics of some of the advanced polymers, are described. Test results and relative rankings of some of the flammability, smoke, and toxicity properties are presented. Under these test conditions, some of the advanced polymers evaluated were significantly less flammable and toxic than or equivalent to polymers in current use.

Kourtides, D. A.↗

NASA NTRS1978

High Temperature Adhesives for Bonding Kapton

Experimental polyimide resins were developed and evaluated as potential high temperature adhesives for bonding Kapton polyimide film. Lap shear strengths of Kapton/Kapton bonds were obtained as a function of test temperature, adherend thickness, and long term aging at 575K (575 F) in vacuum. Glass transition temperatures of the polyimide/Kapton bondlines were monitored by thermomechanical analysis.

Stclair, A. K.↗

NASA NTRS1978

Effects of hydrothermal exposure on a low-temperature cured epoxy

Thermal mechanical analysis was employed to monitor the penetration temperature of a low-temperature epoxy resin. Both neat resin and E-glass composite samples were examined. The effects of cure temperature variation and moisture content on the apparent glass transition temperature were determined.

Lauver, R. W.↗

NASA NTRS1978

Isomer effects on polyimide properties

Thermally stable polyimide polymers were prepared. Parameters explored include asymmetry of substitution, addition of alkyl substituents to an aromatic ring, and an increase in the number of aromatic rings present in the diamine monomer. It is shown that the use of an asymmetrical diamine in the preparation of a polyimide produces a polymer with a markedly lowered glass transition temperature. This is achieved with little or no sacrifice of thermal stability. An alternate approach taken was to prepare imide monomers which are capable of addition-type polymerization.

Stump, B. L.↗

NASA NTRS1977

The effect of moisture on the dynamic thermomechanical properties of a graphite/epoxy composite

A study has been made of the effect of moisture absorption on the dynamic thermomechanical properties of a graphite/epoxy composite recently considered for building primary aircraft structures. Torsional braid analysis (TBA) and thermomechanical analysis (TMA) techniques were used to measure changes in the glass transition temperature (Tg) and the initial softening temperature (heat distortion temperature, HDT) of T-300/5209 graphite/epoxy composites exposed to room temperature water soak.

Sykes, G. F.↗

NASA NTRS1978

Assessment of relative flammability and thermochemical properties of some thermoplastic materials

The thermochemical and flammability characteristics of some typical thermoplastic materials currently in use and others being considered for use in aircraft interiors are described. The properties studied included (1) thermal mechanical properties such as glass transition and melt temperature, (2) changes in polymer enthalpy by differential scanning calorimetry, (3) thermogravimetric analysis in an anaerobic and oxidative environment, (4) oxygen index, (5) smoke evolution, (6) relative toxicity of the volatile products of pyrolysis, and (7) selected physical properties. The generic polymers which were evaluated included: acrylonitrile-butadiene-styrene, bisphenol A polycarbonate, bisphenol fluorenone carbonatedimethylsiloxane block polymer, phenolphthalein-bisphenol A polycarbonate, phenolphthalein polycarbonate, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, polyaryl sulfone, chlorinated polyvinyl chloride homopolymer, polyvinyl fluoride, and polyvinylidene fluoride. Processing parameters including molding characteristics of some of the advanced polymers are described. Test results and relative rankings of some of the flammability, smoke and toxicity properties are presented.

Kourtides, D. A.↗

NASA NTRS1979

Synthesis of aromatic secondary diamines

A series of N-methyl substituted aromatic polyamides derived from the secondary aromatic diamines, 4,4'-bis(methylamino)diphenylmethane, 3,3'-bis(methylamino) diphenylmethane, 4,4'-bis(methylamino)benzophenone or 3,3'-bis(methylamino)benzophenone and isophthaloyl dichloride, terphthaloyl dichloride or 3,3'diphenylmethane dicarboxylic acid dichloride was prepared by high temperature solution polymerization in s-tetrachloroethane. Compared to analogous unsubstituted and partially N-methylated aromatic polyamides, the full N-methylated polyamides exhibited significantly lower glass transition temperatures, reduced crystallinity, improved thermal stability and good solubility in chlorinated solvents.

Wolfe, J. F.↗

NASA NTRS1979

High char imide-modified epoxy matrix resins

The synthesis of a class of bis(imide-amine) curing agents for epoxy matrix resins is discussed. Glass transition temperatures and char yield data of an epoxy cured with various bis(imide-amines) are presented. The room temperature and 350 F mechanical properties, and char yields of unidirectional graphite fiber laminates prepared with conventional epoxy and imide-modified epoxy resins are presented.

Serafini, T. T.↗

NASA NTRS1979

Fabrication of structural elements

The laminate fabrication procedures and quality assurance ultrasonic C-scan results used for structural elements are described. These procedures are the result of processing eleven lots of graphite/PMR-15 prepreg tape materials and two lots of graphite/NR-150B2. Early processing difficulties with NR-150B2 composites were corrected, permitting the fabrication of quality specimens from either of the two currently prescribed matrix materials. The quality of all deliverable specimens is measured by the control of fiber content, glass transition temperature, and void content, as well as laminate ultrasonic C-scan data.

Darms, F. J., Jr.↗

NASA NTRS1978

Effects of hydrothermal exposure on a low-temperature cured epoxy

Thermal mechanical analysis was employed to monitor the penetration temperature of a low-temperature epoxy resin (EPON 826/D230). Both neat resin and E-glass composite samples were examined. The effects of cure temperature variation and moisture content on the apparent glass transition temperature were determined.

Lauver, R. W.↗

NASA NTRS1978

High temperature adhesives for bonding Kapton

Experimental polyimide resins have been developed and evaluated as potential high temperature adhesives for bonding Kapton polyimide film. Lap shear strengths of 'Kapton'/'Kapton' bonds were obtained as a function of test temperature, adherend thickness, and long term aging at 575K (575 F) in vacuum. Glass transition temperatures of the polyimide/'Kapton' bondlines were monitored by thermomechanical analysis.

Saint Clair, A. K.↗

NASA NTRS1978

Measurement requirements and techniques for degradation studies and lifetime prediction testing of photovoltaic modules

Tests of weathering and aging behavior are being developed to characterize the degradation and predict the lifetimes of low-cost photovoltaic arrays. Environmental factors which affect array performance include UV radiation, thermal energy, water, oxygen (generally involved in synergistic effects with UV radiation or high temperatures), physical stress, pollutants (oxides of nitrogen, sulfur dioxide and ozone), abrasives and dirt. A survey of photovoltaic array testing has shown the need to establish quantitative correlations between certain measurable properties (carbonyl formation, glass transition temperature, and molecular weight change) and modes of degradation and failure.

Noel, G. T.↗

NASA NTRS1979

Crystalline polyimides

Aromatic crystalline polyimides are disclosed that are synthesized from polyamide-acid and when heated to 200 C to 300 C become cyclized to afford an opaque polymer. X-ray diffraction of the unoriented film exhibited 47 percent crystallinity. Differential scanning calorimetry reveals a melt at 425 C with no glass transition in these crystalline polyimides.

St.clair, T. L.↗

NASA NTRS1980

Perfluroether triazine elastomers

In order to obtain high performance elastomers with the high thermal stability and chemical inertness of perfluoroalkylene triazine and a low glass transition temperature, perfluoroether triazine elastomers were synthesized. The procedure for elastomer synthesis is described as well as general experimental methods. Results are presented and discussed. The screening of catalysts for the dehydration of perfluoroether diamide is also considered.

Korus, R. A.↗

NASA NTRS1980

The accelerated characterization of viscoelastic composite materials

Necessary fundamentals relative to composite materials and viscoelasticity are reviewed. The accelerated characterization techniques of time temperature superposition and time temperature stress superposition are described. An experimental procedure for applying the latter to composites is given along with results obtained on a particular T300/934 graphite/epoxy. The accelerated characterization predictions are found in good agreement with actual long term tests. A postcuring phenomenon is discussed that necessitates thermal conditioning of the specimen prior to testing. A closely related phenomenon of physical aging is described as well as the effect of each on the glass transition temperature and strength. Creep rupture results are provided for a variety of geometries and temperatures for T300/934 graphite/epoxy. The results are found to compare reasonably with a modified kinetic rate theory.

Griffith, W. I.↗