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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Sulfone/Ester Polymers Containing Pendent Ethynyl Groups

Two processes make high-performance polymers resistant to solvents, without compromising mechanical characteristics. Polymers show improved solvent resistance while retaining high toughness, thermoformability, and mechanical performance. Multistep process involves conversion of pendent bromo group to ethynyl group, while direct process involves reacting hydroxy-terminated sulfone oligomers or polymers with stoichiometric amount of 5-(4-ethynylphenoxy) isophthaloyl chloride. Applications for new polymers include adhesives, composite resin matrices, moldings, ultrafiltration membranes, protective coatings, and such electrical insulators as thin films for microelectronic circuitry.

Hergenrother, P. M.↗
NASA NTRS1986

Investigation of porous polymer gas chromatographic packings for atmospheric analysis of extraterrestrial bodies

Measurement of the permanent gases in the atmospheres of mission targets is a major objective. A 16 meter long Porapak N column was used on the Venus probe and required a rather high carrier gas flow rate. The researchers have, therefore, surveyed commercial porous polymer types which had some ability to resolve nitrogen, oxygen, argon and carbon monoxide gases. Porapaks N and Q appeared superior to most. Batch to batch variation, however, was quite wide, so the researchers learned how to synthesize porous polymer and investigated some of the factors affecting the separations. A polymer was synthesized which was superior to all commercial products and allowed at least a 50% reduction in length and flow rate of carrier gas. Similar studies were made concerning the separation of hydrocarbons and new porous polymers have been synthesized which represent significant improvements in time of analysis, column, and carrier gas flow rate.

Pollock, G. E.↗
NASA NTRS1986

Microgravity Polymers

A one-day, interactive workshop considering the effects of gravity on polymer materials science was held in Cleveland, Ohio, on May 9, 1985. Selected programmatic and technical issues were reviewed to introduce the field to workshop participants. Parallel discussions were conducted in three disciplinary working groups: polymer chemistry, polymer physics, and polymer engineering. This proceedings presents summaries of the workshop discussions and conclusions.

Source record↗
NASA NTRS1985

Computer-aided design of polymers and composites

This book on computer-aided design of polymers and composites introduces and discusses the subject from the viewpoint of atomic and molecular models. Thus, the origins of stiffness, strength, extensibility, and fracture toughness in composite materials can be analyzed directly in terms of chemical composition and molecular structure. Aspects of polymer composite reliability are considered along with characterization techniques for composite reliability, relations between atomic and molecular properties, computer aided design and manufacture, polymer CAD/CAM models, and composite CAD/CAM models. Attention is given to multiphase structural adhesives, fibrous composite reliability, metal joint reliability, polymer physical states and transitions, chemical quality assurance, processability testing, cure monitoring and management, nondestructive evaluation (NDE), surface NDE, elementary properties, ionic-covalent bonding, molecular analysis, acid-base interactions, the manufacturing science, and peel mechanics.

Kaelble, D. H.↗
NASA NTRS1986

Polymer precursors for ceramic matrix composites

The synthesis and characterization of a polycyclohexasilane is reported. Because of its cyclic structure, it is anticipated that this polymer might serve as a precursor to SIC having a high char yield with little rearrangement to form small, volatile cyclic silanes, and, as such, would be of interest as a precursor to SiC composite matrices and fibers, or as a binder in ceramic processing. Several approaches to the synthesis of a bifunctional cyclic monomer were attempted; the most successful of these was metal coupling of PhMeSiCl2 and Me2SiCl2. The procedure gives six-membered ring compounds with all degrees of phenyl substitution, from none to hexaphenyl. The compounds with from 0-2 groups were isolated and characterized. The fraction with degree of phenyl substitution equal to 2, a mixture of cis and trans 1,2-; 1,3-; and 1,4 isomers, was isolated in 32 percent yield. Pure 1,4 diphenyldecamethylcyclohexasilane was isolated from the mixed diphenyl compounds and characterized. Diphenyldecamethylcyclohexasilanes were dephenylated to dichlorodecamethylcyclohexasilanes by treating with H2SO4.NH4Cl in benzene. The latter were purified and polymerized by reacting with sodium in toluene. The polymers were characterized by HPGPC, elemental analysis, proton NMR, and IR. Thermogravimetric analyses were carried out on the polymers. As the yield of residual SiC was low, polymers were heat treated to increase the residual char yield. As high as 51.52 percent residual char yield was obtained in one case.

Litt, M. H.↗
NASA NTRS1988

Decrease in the etch rate of polymers in the oxygen afterglow with increasing gas flow rate

This paper reports the variation of the etch rate of polymers in the afterglow of a radio frequency discharge in oxygen as a function of total flow rate in the range 2-10 cu cm (STP)/min. The measurements were made at ambient temperature with the O(P-3) concentration held essentially constant. Results are reported on three polymers: cis-polybutadiene, a polybutadiene with 33 percent 1,2 double bonds, and a polybutadiene with 40 percent 1,2 double bonds. It has been observed that the etch rate of these polymers decreases significantly with increasing flow rate, strongly suggesting that the vapor-phase products of polymer degradation contribute to the degradation process.

Lerner, N. R.↗
NASA NTRS1989

Predictive aging of polymers

A method of predicting aging of polymers operates by heating a polymer in the outdoors to an elevated temperature until a change of property is induced. The test is conducted at a plurality of temperatures to establish a linear Arrhenius plot which is extrapolated to predict the induction period for failure of the polymer at ambient temperature. An Outdoor Photo Thermal Aging Reactor (OPTAR) is also described including a heatable platen for receiving a sheet of polymer, means to heat the platen, and switching means such as a photoelectric switch for turning off the heater during dark periods.

Cuddihy, Edward F.↗
NASA NTRS1990

LaRC TPI 1500 series polymers

The crystallization behavior and the melt flow properties of two batches of 1500 series LaRC-TPI polymers from Mitsui Toatsu Chemicals (MTC) were investigated. The characterization methods include Differential Scanning Calorimetry, the x ray diffractography and the melt rheology. The as-received materials possess 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 the samples annealed at temperatures above 330 C. Isothermal crystallization kinetics were studied by means of the simple Avrami equation. The viscoelastic properties at elevated temperatures below and above glass transition temperature of the polymers were measured. Information with regard to the molecule sizes and distributions in these polymers were also extracted from melt rheology.

Hou, Tan-Hung↗
NASA NTRS1989

Determinations of molecular weight and molecular weight distribution of high polymers by the rheological properties

Several methods are reviewed by which the molecular weight (MW) and the molecular weight distribution (MWD) of polymeric material were determined from the rheological properties. A poly(arylene ether) polymer with six different molecular weights was used in this investigation. Experimentally measured MW and MWD were conducted by GPC/LALLS (gel permeation chromatography/low angle laser light scattering), and the rheological properties of the melts were measured by a Rheometric System Four rheometer. It was found that qualitative information of the MW and MWD of these polymers could be derived from the viscoelastic properties, with the methods proposed by Zeichner and Patel, and by Dormier et al., by shifting the master curves of the dynamic storage modulus, G', and the loss modulus, G'', along the frequency axis. Efforts were also made to calculate quantitative profiles of MW and MWD for these polymers from their rheological properties. The technique recently proposed by Wu was evaluated. It was found that satisfactory results could only be obtained for polymers with single modal distribution in the molecular weight.

Huang, J. Y.↗
NASA NTRS1991

Polymers And Riblets Reduce Hydrodynamic Skin Friction

Polymers injected into riblet grooves dramatically reduce polymer flow rate required for drag reduction. Polymer solution injected into valleys of grooves through array of holes or slots angled downstream to keep injected streams within grooves. Injection repeated some distance downstream because volumes of grooves finite and polymer becomes depleted as slowly pulled from groove by turbulence. Potentially useful for oil tankers as means of markedly reducing cost of fuel and used extensively on submarines, other ships, and other marine vehicles.

Bushnell, Dennis M.↗
NASA NTRS1991

Nonlinear optical polymers for electro-optic signal processing

Photonics is an emerging technology, slated for rapid growth in communications systems, sensors, imagers, and computers. Its growth is driven by the need for speed, reliability, and low cost. New nonlinear polymeric materials will be a key technology in the new wave of photonics devices. Electron-conjubated polymeric materials offer large electro-optic figures of merit, ease of processing into films and fibers, ruggedness, low cost, and a plethora of design options. Several new broad classes of second-order nonlinear optical polymers were developed at the Navy's Michelson Laboratory at China Lake, California. Polar alignment in thin film waveguides was achieved by electric-field poling and Langmuir-Blodgett processing. Our polymers have high softening temperatures and good aging properties. While most of the films can be photobleached with ultraviolet (UV) light, some have excellent stability in the 500-1600 nm range, and UV stability in the 290-310 nm range. The optical nonlinear response of these polymers is subpicosecond. Electro-optic switches, frequency doublers, light modulators, and optical data storage media are some of the device applications anticipated for these polymers.

Lindsay, Geoffrey A.↗
NASA NTRS1991

Repair of oxidation protection coatings on carbon-carbon using preceramic polymers

The paper describes a field-applicable technique for the repair of damage to SiC protective coatings on carbon/carbon composites, using commercial preceramic polymers, such as perhydropolysilazane developed by the Southwest Research Institute and several commercial polymers (NICALON, PS110, PS116, PS117, NCP-200, and PHPS were tested). After being applied on the damaged panel and oxidized at 1400 C, these polymers form either SiC or Si3N4 (or a mixture of both). It was found that impact damaged carbon/carbon specimens repaired with perhydropolysilazane exhibit substantial oxidation resistance. Many of the other tested preceramic polymer were found to be unsuitable for the purpose of repair due to either low ceramic yield, foaming, or intumescence.

Schwab, Stuart T.↗
NASA NTRS1991

Simulated space environmental effects on some experimental high performance polymers

Organic polymeric materials are currently being considered for long term use (more than 10 years) in structural (adhesives and composite matrices) and functional (films and coatings) applications on spacecraft. Although organic polymers have been utilized successfully in short term missions, the long term durability of these materials in space is of concern. As part of a NASA effort on high performance polymers for potential space applications, various experimental polymeric materials recently synthesized at NASA Langley Research Center were evaluated under simulated space environmental conditions. Experimental resins from blends of acetylene terminated materials, poly(arylene ether)s and low color polyimides were exposed to high energy electron and ultraviolet radiation in an attempt to simulate space environmental effects. Thin films, neat resin moldings and carbon fiber reinforced composites were exposed and the effect on certain polymer properties were determined. This paper reviews recent research involving the effects of various radiation exposures on the physical, optical and mechanical properties of several experimental polymer systems.

Connell, John W.↗
NASA NTRS1993

The electrolyte challenge for a direct methanol-air polymer electrolyte fuel cell operating at temperatures up to 200 C

Novel polymer electrolytes are being evaluated for use in a direct methanol-air fuel cell operating at temperatures in excess of 100 C. The evaluation includes tests of thermal stability, ionic conductivity, and vapor transport characteristics. The preliminary results obtained to date indicate that a high temperature polymer electrolyte fuel cell is feasible. For example, Nafion 117 when equilibrated with phosphoric acid has a conductivity of at least 0.4 Omega(exp -1)cm(exp -1) at temperatures up to 200 C in the presence of 400 torr of water vapor and methanol vapor cross over equivalent to 1 mA/cm(exp 2) under a one atmosphere methanol pressure differential at 135 C. Novel polymers are also showing similar encouraging results. The flexibility to modify and optimize the properties by custom synthesis of these novel polymers presents an exciting opportunity to develop an efficient and compact methanol fuel cell.

Savinell, Robert↗
NASA NTRS1991

Recent developments in high temperature organic polymers

Developments in high temperature organic polymers during the last 5 years with major emphasis on polyimides and poly(arylene ether)s are discussed. Specific polymers or series of polymers have been selected to demonstrate unique properties or the effect chemical structure has upon certain properties. This article is not intended to be a comprehensive review of high temperature polymer advancements during the last 5 years.

Hergenrother, P. M.↗
NASA NTRS1995

An NMR study of microvoids in polymers

An understanding of polymer defect structures, like microvoids in polymeric matrices, is crucial to their fabrication and application potential. In this project guest atoms are introduced into the microvoids in PMR-15 and NMR is used to determine microvoid sizes and locations. Xenon is a relatively inert probe that would normally be found naturally in polymer or in NMR probe materials. There are two NMR active xenon isotopes, Xe-129 and Xe-131. The Xe atom has a very high polarizability, which makes it sensitive to the intracrystalline environment of polymers. Interactions between the Xe atoms and the host matrix perturb the Xe electron cloud, deshielding the nuclei, and thereby expanding the range of the observed NMR chemical shifts. This chemical shift range which may be as large as 5000 ppm, permits subtle structural and chemical effects to be studied with high sensitivity. The Xe(129)-NMR line shape has been found to vary in response to changes in the pore symmetry of the framework hosts line Zeolites and Clathrasil compounds. Before exposure to Xe gas, the PMR-15 samples were dried in a vacuum oven at 150 C for 48 hours. The samples were then exposed to Xe gas at 30 psi for 72 hours and sealed in glass tubes with 1 atmosphere of xenon gas. Xenon gas at 1 atmosphere was used to tune up the spectrometer and to set up the appropriate NMR parameters. A single Xe-129 line at 83.003498 Mhz (with protons at 300 Mhz) was observed for the gas. With the xenon charged PMR-15 samples, a second broader line is observed 190 ppm downfield from the gas line (also observed). The width of the NMR line from the Xe-129 absorbed in the polymer is at least partially due to the distribution of microvoid sizes. From the chemical shift (relative to the gas line) and the line width, we estimate the average void sizes to be 2.74 +/- 0.20 angstroms. Since Xe-129 has such a large chemical shift range (approximately 5000 ppm), we expect the chemical shift anisotropy to contribute to the line width (delta upsilon = 2.5 kHz).

Toy, James↗
NASA NTRS1995

A Dry Powder Process for Preparing Uni-Tape Prepreg from Polymer Powder Coated Filamentary Towpregs

A process for preparing uni-tape prepreg from polymer powder coated filamentary towpregs is provided. A plurality of polymer powder coated filamentary towpregs are provided. The towpregs are collimated so that each towpreg is parallel. The sandwich is heated to a temperature wherein the polymer flows and intimately contacts the filaments and pressure is repeatedly applied perpendicularly to the sandwich with a longitudinal oscillating action wherein the filaments move apart and the polymer wets the filaments forming a uni-tape prepreg. The uni-tape prepreg is subsequently cooled.

Wilkinson, Steven P.↗
NASA NTRS1994

The effect of water on thermal stresses in polymer composites

The fundamentals of the thermodynamic theory of mixtures and continuum thermochemistry are reviewed for a mixture of condensed water and polymer. A specific mixture which is mechanically elastic with temperature and water concentration gradients present is considered. An expression for the partial pressure of water in the mixture is obtained based on certain assumptions regarding the thermodynamic state of the water in the mixture. Along with a simple diffusion equation, this partial pressure expression may be used to simulate the thermostructural behavior of polymer composite materials due to water in the free volumes of the polymer. These equations are applied to a specific polymer composite material during isothermal heating conditions. The thermal stresses obtained by the application of the theory are compared to measured results to verify the accuracy of the approach.

Sullivan, Roy M.↗