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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Polyfunctional epoxies - Different molecular weights of brominated polymeric additives as flame retardants in graphite composites

The imparting of flame retardancy to graphite-reinforced composites without incurring mechanical property deterioration is investigated for the case of an experimental, trifunctional epoxy resin incorporating brominated polymeric additives (BPAs) of the diglycidyl type. Such mechanical properties as flexural strength and modulus, and short beam shear strength, were measured in dry and in hot/wet conditions, and the glass transition temperature, flammability, and water absorption were measured and compared with nonbromilated systems. Another comparison was made with a tetrafunctional epoxy system. The results obtained are explained in terms of differences in the polymeric backbone length of the bromine carrier polymer. BPAs are found to be a reliable bromine source for fire inhibition in carbon-reinforced composites without compromise of mechanical properties.

Nir, Z.↗
NASA NTRS1984

Carbon isotope composition of low molecular weight hydrocarbons and monocarboxylic acids from Murchison meteorite

Carbon isotopic compositions have been measured for individual hydrocarbons and monocarboxylic acids from the Murchison meteorite, a C2 carbonaceous chondrite which fell in Australia in 1969. With few exceptions, notably benzene, the volatile products are substantially isotopically heavier than their terrestrial counterparts, signifying their extraterrestrial origin. For both classes of compounds, the ratio of C-13 to C-12 decreases with increasing carbon number in a roughly parallel manner, and each carboxylic acid exhibits a higher isotopic ratio than the hydrocarbon containing the same number of carbon atoms. These trends are consistent with the kinetically controlled synthesis of higher homologues from lower ones. The results suggest the possibility that the production mechanisms for hydrocarbons and carboxylic acids may be similar, and impose constraints on the identity of the reactant species.

Yuen, G.↗
NASA NTRS1983

Occurrence of low molecular weight thiols in biological systems

Bromobimane labeling and high performance chromatography analysis were applied to various species of bacteria, plant tissues, and animal tissues. The reaction between thiols and monobromobimane is studied. Chromatograms revealing peaks produced by nonthiols and thiols are analyzed and compared. It is observed that all the bacteria species contain hydrogen sulfide, and glutathione is contained in facultative and aerobic gram-negative bacteria. For the plant tissues, the data reveal that mung bean sprouts contain homoglutathione and no glutathione; alfalfa sprouts contain homoglutathione and glutathione; the pea seed, nonlegumes, and fungi contain glutathione and no homoglutathione. It is detected that the main thiol in the animal tissues is glutathione. Based on the data, it is suggested that glutathione has an essential function in higher organisms.

Fahey, Robert C.↗
NASA NTRS1990

Characterization of LaRC-TPI 1500 powders - A new version with controlled molecular weight

The crystallization behavior and the melt flow properties of two batches of 1500 series LaRC-TPI polymers have been investigated. The characterization methods include DSC, XRD, and melt rheology. The as-received materials posses initial crystalline melting peak temperatures of 295 and 305 C, respectively. These materials are less readily recrystallizable at elevated temperatures when compared to other semicrystalline thermoplastics. For the samples annealed at temperatures below 330 C, a semicrystalline polymer can be obtained. On the other hand, a purely amorphous structure is realized in samples annealed at temperatures above 330 C. The viscoelastic properties at elevated temperatures below and above T(g)s of the polymers were measured. Information with regard to the molecule sizes and distributions in these polymers were also extracted from melt rheology.

Hou, T. H.↗
NASA NTRS1993

Extraction and isotopic analysis of medium molecular weight hydrocarbons from Murchison using supercritical carbon dioxide

The large variety of organic compounds present in carbonaceous chondrites poses particular problems in their analysis not the least of which is terrestrial contamination. Conventional analytical approaches employ simple chromatographic techniques to fractionate the extractable compounds into broad classes of similar chemical structure. However, the use of organic solvents and their subsequent removal by evaporation results in the depletion or loss of semi-volatile compounds as well as requiring considerable preparative work to assure solvent purity. Supercritical fluids have been shown to provide a powerful alternative to conventional liquid organic solvents used for analytical extractions. A sample of Murchison from the Field Museum was analyzed. Two interior fragments were used; the first (2.85 g) was crushed in an agate pestel and mortar to a grain size of ca. 50-100 micron, the second (1.80 g) was broken into chips 3-8 mm in size. Each sample was loaded into a stainless steel bomb and placed in the extraction chamber of an Isco supercritical fluid extractor maintained at 35 C. High purity (99.9995 percent) carbon dioxide was used and was pressurized using an Isco syringe pump. The samples were extracted dynamically by flowing CO2 under pressure through the bomb and venting via a 50 micron fused filica capillary into 5 mls of hexane used as a collection solvent. The hexane was maintained at a temperature of 0.5 C. A series of extractions were done on each sample using CO2 of increasing density. The principal components extracted in each fraction are summarized.

Gilmour, Iain↗
NASA NTRS2004

Chemistry, Adhesive and Composite Properties of Low Molecular Weight Phenylethynyl Terminated Oligomers

PETI-5 (1250 and 2500 g/mole) were prepared and characterized. Neat resin, adhesive and composite properties were determined and compared with those of PETI-5 (5000 g/mole). Relative to PETI-5 (5000 g/mole), PETI-5 (2500 g/mole) exhibited improved processability and equivalency in the adhesive and composite properties measured thus far. This resin, in both adhesive film and prepreg form, has the potential to offer significant improvements in the processing of complex structural composite parts.

Connell, John W.↗
NASA NTRSDate not supplied

A Cold Wet Mars: A Testable Hypothesis for Ancient Mars Ocean Freezing Point Depression Via Low Molecular Weight Organics

Mars exhibits widespread evidence of surface water in the distant past, but global modeling has had difficulty producing climatological conditions conducive to a wet surface. The hypothesis discussed here examines a different way of approaching the problem rather than focusing on climate, instead an examination of the nature of the surface liquid itself. Previous work has largely assumed that martian surface water was a brine analogous to terrestrial ocean water, but recent discoveries suggest that significant amounts of light organic compounds may have been present via abiogenic native production of light organics on Mars [1]. Light organics such as methanol and formaldehyde have an approximate order-of-magnitude greater freezing point depression than brine, potentially lowering the freezing point of martian surface fluids sufficiently to remain liquid even if the mean surface temperature is below zero Centigrade. As Mars evolved and the surface transitioned to the strongly oxidized conditions seen today, the light organics would have oxidized to carbon dioxide and may be a constituent of the atmosphere today. Considerable work must be done to constrain the freezing points of Mars-relevant organic/water and organic/salt/water mixtures, but this investigation might explain the presence of surface fluid on a cold early Mars – a cold, wet Mars as opposed to a warm, wet Mars. Additionally, this approach may work in conjunction with climatological modeling to better describe early conditions conducive which adequately explain observations. This hypothesis can be tested by examination of ancient fluid inclusions (either in situ or via Mars Sample Return) such as those commonly found in halite, preserving samples of ancient martian surface fluid.

M D Fries↗
DOE OSTI2021

Surface treatment of ultra-high molecular weight polymers

The methods and compounds disclosed herein relate to the surface modification of UHMWPs by means of a catalytic C—H bond insertion catalyst using a rhodium catalysts in conjunction with carbene-generating diazo compounds. The catalytic treatment imparts covalently added functionality to the UHMWPE surface. This functionality acts as an excellent grafting mechanism for grafting, bonding, or adhering further materials to the UHMWPs surface.

O'Bryan, Greg↗