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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

NMR Guided Design of Endcaps With Improved Oxidation Resistance

A polyimide is a polymer composed of alternating units of diamine and dianhydride, linked to each other via an imide bond. PMR polyimides, commonly used in the aerospace industry, are generally capped at each end by a norbornene endcap which serves a double function: (1) It limits the number of repeating units and, hence, the average molecular weight of the various polymer chains (oligomers), thereby improving processibility; (2) Upon further treatment (curing), the endcap crosslinks the various oligomer strands into a tough heat-resistant piece. Norbornenyl-end capped PMR polyimide resins' are widely used as polymer matrix composite materials for aircraft engine applications,2 since they combine ease of processing with good oxidative stability up to 300 C. PMR resins are prepared by a twestep approach involving the initial formation of oligomeric pre-polymers capped at both ends by a latent reactive end cap. The end cap undergoes cross-linking during higher temperature processing, producing the desired low density, high specific strength materials, as shown for PMR-15.

Meador, Mary Ann B.↗
NASA NTRS1988

The development of new, low-cost perfluoroalkylether fluids with excellent low and high-temperature properties

A series of perfluoroalkylether (PFAE) fluids were synthesized by direct fluorination. Viscosity-temperature properties, oxidation stabilities, oxidation-corrosion properties, and lubricity were determined. The fluids were tested in the presence of common elastomers to check for compatibility. The bulk modulus of each was measured to determine if any could be used as nonflammable aircraft hydraulic fluid. It was determined that as the carbon to oxygen ratio decreases, the viscometric properties improve, the fluids may become poor lubricants, the bulk modulus increases, the surface tension increases, and the fluid density increases. The presence of difluoromethylene oxide units in the polymer does not seriously lower the oxidation and oxidation-corrosion stabilities as long as the difluoromethylene oxide units are separated by other units.

Bierschenk, Thomas R.↗
NASA NTRS2005

Novel Elastomeric Membranes Developed for Polymer Electrolytes in Lithium Batteries

Lithium-based polymer batteries for aerospace applications need to be highly conductive from -70 to 70 C. State-of-the-art polymer electrolytes are based on polyethylene oxide (PEO) because of the ability of its ether linkages to solvate lithium ions. Unfortunately, PEO has a tendency to form crystalline regions below 60 C, dramatically lowering conductivity below this temperature. PEO has acceptable ionic conductivities (10(exp -4) to 10(exp -3) S/cm) above 60 C, but it is not mechanically strong. The room-temperature conductivity of PEO can be increased by adding solvent or plasticizers, but this comes at the expense of thermal and mechanical stability. One of NASA Glenn Research Center s objectives in the Polymer Rechargeable System program (PERS) is to develop novel polymer electrolytes that are highly conductive at and below room temperature without added solvents or plasticizers.

Tigelaar, Dean M.↗
NASA NTRS1999

Approaches to New Endcaps for Improved Oxidation Resistance

Norbornenyl-end capped PMR polyimide resins are widely used as polymer matrix composite materials for aircraft engine applications, since they combine ease of processing with good oxidative stability up to 300 C. PMR resins are prepared by a two-step approach involving the initial formation of oligomeric pre-polymers capped at both ends by a latent reactive end cap. The end cap undergoes cross-linking during higher temperature processing, producing the desired low density, high specific strength materials, for PMR- 15. The end cap facilitates processing by controlling the molecular weight of the oligomer and allowing flow before it cross-links. However, after cross-linking, this very end cap accounts for much of the weight loss in the polymer on aging in air at elevated temperatures. Understanding this degradation provides clues for designing new end caps to slow down degradation, and prolong the lifetime of the material.

Meador, Mary Ann B.↗
NASA NTRS2021

Effect of High Temperature Storage on AC Characteristics of Polymer Tantalum Capacitors

Replacement of MnO2 with conductive polymers as cathode materials in chip tantalum capacitors allows for a substantial reduction of the equivalent series resistance (ESR), improvement of frequency characteristics, and elimination of the possibility of ignition during failures. One of the drawbacks of chip polymer tantalum capacitors (CPTCs) is a relatively poor long-term stability at high temperatures. In this work, variations of capacitance, dissipation factor, and ESR in different types of capacitors including automotive grade parts from three manufacturers have been monitored during storage at temperatures from 100 ºC to 175 ºC for up to 18,000 hours. Results show that ESR is the most and capacitance the least sensitive to degradation parameter. Times to parametric failures have been simulated using a Weibull-Arrhenius model that allowed for assessments of activation energies of the degradation and prediction of times to failure at the use temperature. Degradation of CPTCs was explained by thermo-oxidative processes in conductive polymers that result in exponential increasing of the resistivity with time of ageing. This process starts after a certain incubation period that depends on packaging materials and design and corresponds to the time that is necessary to form delamination between the encapsulating molding compound and lead frame. The effectiveness of the existing qualification procedures to assure stable operation of CPTCs is discussed.

Alexander A Teverovsky↗
NASA NTRSDate not supplied

Effect of High Temperature Storage on AC Characteristics of Polymer Tantalum Capacitors

Replacement of MnO2 with conductive polymers as cathode materials in chip tantalum capacitors allows for a substantial reduction of the equivalent series resistance (ESR), improvement of frequency characteristics, and elimination of the possibility of ignition during failures. One of the drawbacks of chip polymer tantalum capacitors (CPTCs) is a relatively poor long-term stability at high temperatures. In this work, variations of capacitance, dissipation factor, and ESR in different types of capacitors including automotive grade parts from three manufacturers have been monitored during storage at temperatures from 100 ºC to 175 ºC for up to 18,000 hours. Results show that ESR is the most and capacitance the least sensitive to degradation parameter. Times to parametric failures have been simulated using a Weibull-Arrhenius model that allowed for assessments of activation energies of the degradation and prediction of times to failure at the use temperature. Degradation of CPTCs was explained by thermo-oxidative processes in conductive polymers that result in exponential increasing of the resistivity with time of ageing. This process starts after a certain incubation period that depends on packaging materials and design and corresponds to the time that is necessary to form delamination between the encapsulating molding compound and lead frame. The effectiveness of the existing qualification procedures to assure stable operation of CPTCs is discussed.

Aging↗
NASA NTRSDate not supplied

Effect of High Temperature Storage on AC Characteristics of Polymer Tantalum Capacitors

Replacement of MnO2 with conductive polymers as cathode materials in chip tantalum capacitors allows for a substantial reduction of the equivalent series resistance (ESR), improvement of frequency characteristics, and elimination of the possibility of ignition during failures. One of the drawbacks of chip polymer tantalum capacitors (CPTCs) is a relatively poor long-term stability at high temperatures. In this work, variations of capacitance, dissipation factor, and ESR in different types of capacitors including automotive grade parts from three manufacturers have been monitored during storage at temperatures from 100 ºC to 175 ºC for up to 18,000 hours. Results show that ESR is the most and capacitance the least sensitive to degradation parameter. Times to parametric failures have been simulated using a Weibull-Arrhenius model that allowed for assessments of activation energies of the degradation and prediction of times to failure at the use temperature. Degradation of CPTCs was explained by thermo-oxidative processes in conductive polymers that result in exponential increasing of the resistivity with time of ageing. This process starts after a certain incubation period that depends on packaging materials and design and corresponds to the time that is necessary to form delamination between the encapsulating molding compound and lead frame. The effectiveness of the existing qualification procedures to assure stable operation of CPTCs is discussed.

Aging↗
NASA NTRS2021

Effect of High Temperature Storage on AC Characteristics of Polymer Tantalum Capacitors

Replacement of MnO2 with conductive polymers as cathode materials in chip tantalum capacitors allows for a substantial reduction of the equivalent series resistance (ESR), improvement of frequency characteristics, and elimination of the possibility of ignition during failures. One of the drawbacks of chip polymer tantalum capacitors (CPTCs) is a relatively poor long-term stability at high temperatures. In this work, variations of capacitance, dissipation factor, and ESR in different types of capacitors including automotive grade parts from three manufacturers have been monitored during storage at temperatures from 100 ºC to 175 ºC for up to 18,000 hours. Results show that ESR is the most and capacitance the least sensitive parameter to degradation. Times to parametric failures have been simulated using a Weibull-Arrhenius model that allowed for assessments of activation energies of the degradation and prediction of times to failure at the use temperature. Degradation of CPTCs was explained by thermo-oxidative processes in conductive polymers that result in exponential increase of the resistivity with time of aging. This process starts after a certain incubation period that depends on packaging materials and design and corresponds to the time that is necessary to form delamination between the encapsulating molding compound and lead frame. The effectiveness of the existing qualification procedures to assure stable operation of CPTCs is discussed.

high temperature storage (HTS)↗
NASA NTRS1979

Investigation of Test Methods, Material Properties, and Processes for Solar Cell Encapsulants

The reformulation of a commercial grade of ethylene/vinyl acetate copolymer for use as a pottant in solar cell module manufacture was investigated. Potentially successful formulations were prepared by compounding the raw polymer with antioxidants, ultraviolet absorbers and crosslinking agents to yield stabilized and curable compositions. The resulting elastomer was found to offer low cost (approximately $0.80/lb.), low temperature processability, high transparency (91% transmission), and low modulus. Cured specimens of the final formulation endured 4000 hours of fluorescent sunlamp radiation without change which indicates excellent stability.

Willis, P. B.↗
NASA NTRS1986

Composite tubes for the Space Station truss structure

The reference configuration of NASA's Space Station includes a large truss structure to support the various modules and solar arrays. This truss structure will be constructed from tubular members approximately 2 in. in diameter and up to 23 ft in length. The important design considerations for this structure are light weight, high stiffness, dimensional stability, and long-term durability. Continuous graphite fiber reinforced polymer matrix composite materials can meet the structural requirements, and are leading candidates for the tubular truss members. However, there are concerns regarding the durability of composites during the long-term exposure to atomic oxygen and thermal cycling that will be encountered during the Space Station service life. This paper discusses space environmental factors and their effect on composite materials, and provides estimates of the changes in mechanical and thermal properties of composites exposed to long-term Space Station conditions. The effect of low velocity impact and handling damage on composite tube properties is also discussed.

Bowles, David E.↗
NASA NTRS2000

Method to Prepare Processable Polymides with Reactive Endgroups using 1,3-Bis (3-Aminophenoxy) Benzene

Polyimide copolymers were obtained containing 1,3-bis(3-aminophenoxy)benzene (APB) and other diamines and dianhydrides and terminating with the appropriate amount of reactive endcapper. The reactive endcappers studied include but should not be limited to 4-phenylethynyl phthalic anhydride (PEPA ), 3-aminophenoxy- 4'-phenylethynylbenzophenone (3-APEB), maleic anhydride (MA) and nadic anhydride (5-norbomene-2,3-dicarboxylic anhydride, NA). Homopolymers containing only other diamines and dianhydrides which are not processable under conditions described previously can be made processable by incorporating various amounts of APB, depending on the chemical structures of the diamines and dianhydrides used. By simply changing the ratio of APB to the other diamine in the polyimide backbone, a material with a unique combination of solubility, Tg, Tm, melt viscosity, toughness and elevated temperature mechanical properties can be prepared. The copolymers that result from using APB to enhance processability have a unique combination of properties that include low pressure processing (200 psi and below), long term melt stability (several hours at 300 C. for the phenylethynyl terminated polymers), high toughness, improved solvent resistance, improved adhesive properties, and improved composite mechanical properties. These copolyimides are eminently suitable as adhesives, composite matrices, moldings, films and coatings.

Jensen, Brian J.↗
NASA NTRS2001

Method To Prepare Processable Polyimides With Reactive Endogroups Using 1,3-bis(3-aminophenoxy)benzene

Polyimide copolymers were obtained containing 1,3-bis(3-aminophenoxy)benzene (APB) and other diamines and dianhydrides and terminating with the appropriate amount of reactive endcapper. The reactive endcappers studied include but should not be limited to 4-phenylethynyl phthalic anhydride (PEPA), 3-aminophenoxy-4'phenylethynylbenzophenone (3-APEB), maleic anhydride (MA) and nadic anhydride (5-norbomene-2,3-dicarboxylic anhydride, NA). Homopolymers containing only other diamines and dianhydrides which are not processable under conditions described previously can be made processable by incorporating various amounts of APB, depending on the chemical structures of the diamines and dianhydrides used. By simply changing the ratio of APB to the other diamine in the polyimide backbone, a material with a unique combination of solubility, Tg, Tm, melt viscosity, toughness and elevated temperature mechanical properties can be prepared. The copolymers that result from using APB to enhance processability have a unique combination of properties that include low pressure processing (200 psi and below), long term melt stability (several hours at 300° C. for the phenylethynyl terminated polymers), high toughness, improved solvent resistance, improved adhesive properties, and improved composite mechanical properties. These copolyimides are eminently suitable as adhesives, composite matrices, moldings, films and coatings.

Brian J Jensen↗
NASA NTRS1998

Synthesis of Polymers Containing Covalently Bonded NLO Chromophores

Polymers containing covalently bonded nonlinear optical (NLO) chromophores are expected to possess special properties such as greater stability, better mechanical processing, and easier film formation than their non-polymeric equivalent. For the present work, polymethylmethacrylate (PMMA) was selected as the basic polymer unit on which to incorporate different NLO chromophores. The NLO components were variations of DIVA {[2-methoxyphenyl methylidene]-propanedinitrile} which we prepared from vanillin derivatives and malononitrile. These were esterified with methacrylic acid and polymerized either directly or with methyl methacrylate to form homopolymers or copolymers respectively. Characterization of the polymers and NLO property studies are underway.

Denga, Xiao-Hua↗
NASA NTRS1988

Initial adhesive screening of novel polyamide-imides and their copolymers

Continued interest by the research community in thermally stable, tough, high temperature adhesives has resulted in the investigation by Langley Research Center of two linear aromatic polyamide-imide (PAI) homopolymers and two linear aromatic PAI copolymers. The homopolymers were made with either 3,3'=DABA or 4,4'-DABA and BTDA. The two polymers were prepared with a monomer ratio of 0.75 DABP:0.25 DABA:1.00 BTDA. These aromatic PAIs possess high thermal stability because of intermolecular hydrogen bonding and chain stiffness. Lap shear strength (LSS) was the main criteria used to evaluate the polymers as adhesives. LSS of bonded Ti-6Al-4V was determined at room temperature (RT), 177, 204 and 232 C. The glass transition temperature and the type of bond failure were also determined. The best LSS values of the four adhesive systems investigated were obtained with the PAI copolymer identified in the report as LARC-TPI (25 percent 3,3'-DABA); however, it did not produce LSSs nearly as high as LARC-TPI. The poor flow properties observed appear to be due to a combination of high molecular weight and the increased interchain electronic interactions associated with the amide group.

Donald J Progar↗
NASA NTRS1989

Initial evaluation of novel polyamide-imides and their copolymers as adhesives

Continued interest by the research community in thermally stable, tough, high temperature adhesives has resulted in the investigation by Langley Research Center of two linear aromatic polyamide-imide (PAI) homopolymers and two linear aromatic PAI copolymers. The homopolymers were made with either 3,3'=DABA or 4,4'-DABA and BTDA. The two polymers were prepared with a monomer ratio of 0.75 DABP:0.25 DABA:1.00 BTDA. These aromatic PAIs possess high thermal stability because of intermolecular hydrogen bonding and chain stiffness. Lap shear strength (LSS) was the main criteria used to evaluate the polymers as adhesives. LSS of bonded Ti-6Al-4V was determined at room temperature (RT), 177, 204 and 232 C. The glass transition temperature and the type of bond failure were also determined. The best LSS values of the four adhesive systems investigated were obtained with the PAI copolymer identified in the report as LARC-TPI (25 percent 3,3'-DABA); however, it did not produce LSSs nearly as high as LARC-TPI. The poor flow properties observed appear to be due to a combination of high molecular weight and the increased interchain electronic interactions associated with the amide group.

Progar, Donald J.↗
NASA NTRS1973

Thermomechanical behavior of a polynorbornadiene

A high-temperature linear amorphous hydrocarbon polymer synthesized cationically from 2,5-norbornadiene was studied thermomechanically with respect to physical transitions and stability in nitrogen. The glass transition temperature was determined to be 320 C (at less than 1 cps), which is probably the highest known for a linear hydrocarbon addition polymer. The thermomechanical technique of torsional braid analysis, together with thermogravimetric analysis, differential thermal analysis, infrared analysis, and solubility studies, was used to investigate the sequential events of the glass transition and degradation. The polymer is of particular interest since it is a high-temperature plastic which in the bulk form would probably need to be processed at high speeds in the vicinity of the glass transition temperature in an inert atmosphere. The presence of tertiary hydrogen atoms should render it amenable to degradation by the earth's environment.

Roller, M. B.↗
NASA NTRS1982

Polymer research at NASA Langley Research Center

Polymer synthesis programs involve the development of Novel thermoplastics, pseudothermoplastics, and thermosets. These systems are prepared to elucidate structure-property relationships involving thermal capabilities, toughness, processability and environmental stability. Easily processable polyimides, solvent-resistant polysulfones and polyphenylquinoxalines, and tougher high and intermediate temperature polymers were developed. Characterization efforts included high pressure liquid chromatography methodology, the development of toughness tests for fiber reinforced composites, a study of electrical properties of metal ion filled polyimides, and a study of the mutagenicity of aromatic diamines. Also the mechanism of cure/degradation of experimental polymers was studied by rheology, mechanical behavior, separation techniques and spectroscopy. The degradative crosslinking of alkyl-containing polyimides, the separation and identification of crosslinked phenylquinoxalines, the rheological behavior of hot-melt polyimides, and the elucidation of the cure of norbornene endcapped imides were also studied.

Terry L. St. Clair↗